Thursday, 20 July 2017

The Everest-Lifeboat Test (Easter Egg - Investigating apparent faints in children)

Paediatric guidelines always have to take into account one of the most important maxims of Child Health - the test or treatment must always be in the best interest of the child.  This means a particular discernment about the value of a test or treatment.  Guidelines rarely discriminate between which treatments and tests are essential and which are simply recommended.  When writing a guideline, it is relatively easy to put in a recommendation, often giving the impression that it is a must-do when this is simply not the case.

One of the things that I am most often asked (whether at work or giving and educational session) is "Do I have to do X?  The guideline says to but..."  So how does one discriminate between the must-do's and the would-be-good-if we-could recommendations?  That's easy - apply the Everest-Lifeboat Test.

The Everest-Lifeboat Test is simply a two part thought exercise.  The first part is to ask the following question:  If the person involved was at an advanced stage of climbing Everest, should they turn back to get this test or treatment or could they reasonably continue to the summit?  This part of the test asks if we are doing something just because we can rather than because we have to.  We are purely focusing on the immediate need at this point.

The second part is the lifeboat question:  Imagine that this patient was in a lifeboat, drifting across the ocean.  When they are rescued several weeks later, would they most likely be fine despite their current clinical situation?  This part of the Everest-Lifeboat Test forces us to look forward and consider the medium and long term consequences of action versus inaction.

Let's try this on a fictional patient.

A 10 year old child is brought to you having had an unexplained collapse.  The history given to you is vague and there is no first hand account of the episode as it happened in front of classmates at school.  However, in your further history taking, you find that this child has been having headaches that are worse in the morning.  Also, teachers have noticed that there has been a deterioration in performance at school over the past four weeks.  The child is slightly ataxic and has nystagmus on examination.

Concerned, you discuss the need for further investigations.  In response, the parents say that they are happy to get the tests done but could it please wait a few weeks?  They were just coming to get a medical opinion before they catch a plane to go away for a couple of weeks for their holiday.  They were assuming that this was just a fainting episode and really only came to get their child checked because grandma told them to.

So, what do you think?  This seems like a clear fail of the Everest-Lifeboat Test to me.  I wouldn't be happy to put investigations on hold, despite the obvious inconvenience to the family.

How about this scenario?:

A 12 year old girl comes to be assessed.  She was in school and had been stood in the heat when she began to feel sweaty and nauseous.  Her vision went black and she slumped to the floor.  She was reported to look pale and floppy.  She was unresponsive for a few seconds and then came around slowly over a few minutes.  A few hours later, she feels fine.  There is no history of unexplained deaths in her family.  When you examine her, all is normal.

You check a relevant guideline and see that it recommends that you perform a 12 lead ECG. She flatly refuses to have this test done and will not be persuaded.  What should you do?

Applying the Everest-Lifeboat test would go like this:

Would you advise abandoning the final attempt on the summit?  Well, she had an obvious precipitant and prodrome for her apparent faint.  We can advise how to avoid precipitants and what to do if a prodrome is recognised.  The event appears to be a classical vasovagal syncope without red flags in the history or examination.  So, forcing the issue seems to be unnecessary.

Would a few weeks in a lifeboat be an issue?  This brings us back to the guidelines that recommend investigation.  What are they trying to protect us from?  Much of the practice of ECG screening comes from adult medicine, where pathology is much more likely.  In paediatrics, there are a few arrhythmias that we need to worry about, but a standard 12 lead ECG is not the perfect screening test that we might hope it is.  The sensitivity and specificity of 12 lead ECGs in children is poor (1).  Ask yourself why the guidelines don't say, "Don't bother with history and examination.  The ECG is the crucial bit of information."

A quick look at the guidelines gives some useful insights to help us with the Everest-Lifeboat Test.  The NICE guideline "Transient loss of consciousness (‘blackouts’) management in adults and young people" (2) actually only relates to the over 16 year-olds.  This in itself acknowledges that an adult approach cannot be extrapolated to the child who has had a collapse.

Then there is the European Society of Cardiology's guideline for the diagnosis and management of syncope (version 2009). (3) It does take the view that children and adults can be investigated similarly and recommends ECG for all children who have had a faint.  However, this recommendation seems to be based on the assumption that an ECG is clearly useful additional information and fails to consider the possibility that a thorough history and examination gets you to a point where and ECG would not add value.

The American College of Cardiology/American Heart Association guideline (4) does seem to consider this possibility.  There is a strong emphasis on the value of a good history and examination.  Regarding ECG, it points out that ECG is a simple and available test that might identify a tendency to arrhythmia.  However it also states: "Despite the benefit of identifying a likely cause or potential clue about the cause of syncope from the ECG, prospective studies did not conclude that ECG findings significantly affected subsequent management.  The prognostic value of an abnormal ECG in patients with syncope has been questioned as well."

So there it is.  An honest declaration that, while the experts would recommend that we all do a test, it is unclear what the value of the test is.

I know that it might seem as though I just want to avoid doing work here, but there are genuine risks with tests.  The first risk is that they stop us from thinking.  If the sensitivity and specificity of history and examination is excellent, while that of ECG is poor, why introduce a deceptive piece of information?  The second risk is that of getting information that I don't want.  If I do an ECG on a child, it is almost always to look at the rate, rhythm and QT interval.  While those things are usually fine, the diagnostic report usually sports a bit of LVH and right atrial enlargement.  Of course the child has neither of these things, but the machine is just trying to make sense of the voltage it has been given.  If I were to take these things seriously, I might cause unnecessary anxiety for the child and parents.

So, what does my patient really need?  I need to take a good history and establish that the episode that sounds like a faint truly sounds like a faint.  This means asking about the three P's of vasovagal syncope.
If it sounds like a classic faint, I still need to make sure that I consider my red flags.
If the history given is of a straightforward faint, without red flags, I think that allowing the child to refuse the ECG passes the Everest-Lifeboat Test.

When we are forced out of our normal process, it is a good time to evaluate our routine practice.  If a deviation from the norm passes the Everest-Lifeboat Test, I would question the norm.  You may just have discovered that you are doing a test or a treatment that you don't believe in.  Here is a little list of things that have passed the Everest-Lifeboat Test for me at various times in the past (i.e. I was going to treat, something got in the way of that and I went with the the no treatment option):
That's a short list of times when the option of doing nothing became the right thing despite what was routine practice.  In the case of umbilical granuloma, I am pleased to say that doing nothing is now becoming the norm.

I hope that you find the Everest-Lifeboat Test useful at some point.  As to whether every child who has had a faint needs an ECG, versus it is good to get one or it is simply not needed unless there is a specific reason - this is a debate that is lacking input from the good people of the primary care and emergency medicine communities.  My solution?  Stick a cardiologist, a paediatrician, an emergency medicine doctor and a general practitioner in a lifeboat and leave them there till they've sorted it out.  I'm fairly sure they'd be fine...

Edward Snelson

Disclaimer: The Everest-Lifeboat Test was originally described in 1055 by Egbert the Uncertain, a monk who died at the Battle of Hastings before writing down his idea.  I therefore take full credit for inventing the test myself.

  1. Kapoor WN, Evaluation and outcome of patients with syncope, Medicine, 1990 May;69(3):160-75.
  2. NICE guideline "Transient loss of consciousness (‘blackouts’) management in adults and young people"
  3. Diagnosis and management of syncope, European Society of Cardiology, European Heart Journal (2009) 30, 2631–2671
  4. Guideline for the Evaluation andManagement of Patients With Syncope,  A Report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines, and the Heart Rhythm Society

Thursday, 29 June 2017

The Truth about Lactose Intolerance

Sometimes, when I'm checking my facts, I'm surprised to find conflicting information.  Sometimes this is because there are no facts and this information void is filled with opinion or speculation.   Sometimes there are myths that confuse the picture and sometimes the information is being interpreted differently by different people.  Lactose intolerance in children is one paediatric condition that is described very differently in various places.  So what is the truth of it?

Let's start with the basics.  Lactose Intolerance (LI) and Cow's Milk Protein Allergy (CMPA) are very different problems but are often confused with each other.  The simple difference is that you can't be allergic to a sugar.  In CMPA there are two different types of immune response possible.  The one that usually gets confused with LI is the non-IgE CMPA because it causes similarly vague and non-specific symptoms.

Lactose intolerance is essentially a budgeting problem.  Breast milk and formula milk contain the sugar lactose.  This provides ready energy and makes the milk taste nice.  To break down lactose, you need an amount of lactase which is proportionate to the amount of milk you consume.  This lactase comes from two sources.  Breast milk contains some lactase, but the majority of lactase that is required is produced in the villi of the small bowel.  

The maths is simple.  If you have enough lactase to deal with the lactose that you consume, all is well.  If you don't, then undigested lactase passes through to the large bowel.  In the colon, bacteria ferment the sugar- causing diarrhoea, abdominal pain and bloating.  (Interestingly, this is also how lactulose works, despite what you may have been told - details about that here)

How lactose intolerance works is well established.  What is far more unclear is how common it is in children and what the underlying cause is when it is present.  In order to understand all of that, it's worth knowing the evolutionary history of lactose intolerance.  Since man has only been farming animals for the past few thousand years, the need to digest lactose into adulthood is a relatively recent phenomenon.  The default physiological norm was for lactase production to diminish and stop after infancy.  Most people now have a lactase persistence gene which allows the small bowel to continue to produce lactase.

There are three types of Lactose Intolerance (1)

1- Primary hypolactasia

This is caused by the absence of the gene that causes ongoing lactase production.  When lactase production wanes, symptoms will come on gradually.

2 - Secondary hypolactasia

This is caused by damage to the small bowel.  In many cases this is the result of a gastroenteritis infection.  Secondary hypolactasia can also be the result of damage caused by non-IgE food allergies.  There is nothing inherently wrong with the child's ability to make lactase, but the small bowel wall that does that has been stripped.  The symptoms of secondary hypolactasia resolve when the damage to the small bowel is repaired.  In the case of post gastroenteritis LI, a few weeks lactose free will help that considerably.

3 - Primary congenital alactasia

This is an autosomal recessive genetic defect resulting in the complete absence of lactase production.  This is extremely rare and according to the experts, there have been less than 100 case reported worldwide. (2)

So here's my problem - sometimes, none of the three known entities fit.  I see lots of parents who report symptoms which are being associated with the child's (usually formula) feed.  They are then absolutely convinced that a lactose free formula has suddenly resolved their infant's problem.  Discuss...

Of course the type of lactose intolerance only matters in terms of deciding whether the child will need long term or short term avoidance.  Secondary hypolactasia should resolve, leaving the child able to resume business as usual once the damaged small intestine has repaired itself.  In general terms, the treatment for LI is the same - remove lactose from the diet.  Nevertheless, the fact that children seem to fit the bill for lactose intolerance without fitting any of the known entities is perplexing.

(Screenshot taken from Wikipaedia on 27/06/2017)

One possible explanation for this is that these children do not have lactose intolerance at all.  Instead the diagnosis has been suspected based on non-specific symptoms, and the resolution of these symptoms following the start of a lactose free milk was coincidence.

As well as the children who have no pathology, there is the group who are labelled as lactose intolerant when what is really wrong with them is something else such as reflux disease (GORD) or Cow's Milk Protein Allergy (CMPA).  Wouldn't it be nice to be able to be sure which condition was affecting the child?

There are tests available for lactose intolerance but they are not readily available in primary care, whereas a therapeutic trial is always a tempting option. The tests used in secondary care seem to vary around the world.  Hydrogen breath testing is a pain free way of testing but impractical  in infants making it unhelpful in most cases.  A lactose tolerance test involves giving a large dose of lactose and then doing serial blood glucose measurements.  A lactose challenge does the same but relies on the witnessing of symptoms following the administration of lactose to the child.

In the UK, the vast majority of LI diagnoses are made on clinical suspicion and treated by an exclusion diet.  The difficulty with this is the risk of overdiagnosis when using this strategy.  Symptoms often change with time and so any apparent improvement following an exclusion of lactose from the diet should probably be challenged in every case.

So what is the truth about Lactose Intolerance?  Is is frequently being diagnosed in contradiction of sound medical understanding of the condition?  Is there a significant number of infants who don't fit into the three categories described above but still have genuine LI?

I think that the presumption should be that a baby who has significant symptoms (other than the classic LI symptoms following a gastroenteritis) should have another explanation sought.  They may have GORD or CMPA but it doesn't make sense that they should have lactose intolerance unless there is a form of this condition that is as yet not understood or well described.

Edward Snelson
Congenitally Tolerant Clinician

Hot tip - if a lactose intolerant baby is breast fed, there is no point in excluding milk from the mother's diet in an attempt to resolve this.  Breast milk produces its own lactose.  If the diagnosis is convincing, try supplementing the lactase.  If you want to know where to find it, lactase is the 'active ingredient' in some colic treatments.  It doesn't actually treat colic but that is another story.  At least it has a use here.

  1. Heyman B et al, Lactose Intolerance in Infants, Children, and Adolescents, Pediatrics, Vol 118, Number 3, p 1279-1286, September 2006
  2. Deng, Y et al, Lactose Intolerance in Adults: Biological Mechanism and Dietary Management, Nutrients. 2015 Sep; 7(9): 8020–8035.

Tuesday, 13 June 2017

Think Sepsis - What does that mean?

You may have noticed that there are a lot more paediatric sepsis guidelines flying around these days.  When people write guidelines, they are trying to be helpful but it is always worth knowing why they decided to be helpful.  For example, guidelines for diagnosis of asthma in childhood are strongly motivated by the desire to reduce the overdiagnosis of asthma in childhood.  We know this because the guideline writers tell us.  They're quite good like that.

So what about sepsis?  Well there are two genuine problems that keep coming up around sepsis:
  • Early diagnosis of sepsis
  • Early and aggressive treatment of sepsis
There's probably more to it than that but that is the main thrust of what most sepsis guidelines are trying to achieve.

I think that the guidelines that have come out over the past few years have done a good job in guiding our management of sepsis.  Once you have decided a child has enough evidence of being septic to be treated, crack on and don't spare the horses.  There is no doubt that as a profession, we are getting our act together in this respect.

The first part is more tricky. diagnosing sepsis is difficult.  Sorry, let's be honest, it is really, really difficult.  Sepsis is missed all the time, and I am not talking about the overdiagnosis of missed sepsis which goes like this:

There is a two part truth which guideline writers and readers need to accept.  Sepsis is often missed because it is often easy to miss it.

So, back to the guideline writing - in order to help us diagnoses sepsis, guidelines have been written to help us to recognise sepsis.  As a colleague of mine recently pointed out, that only works if you know to look at the sepsis guideline.  If you are already looking at the sepsis guideline then the battle is already won, because if you are worried enough to look at the sepsis guideline, it's usually time to phone a friend.

So why is it easy to miss sepsis?  There are several reasons;
  • The diagnosis of sepsis is subjective.  There is no mathematical equation (Fever + Tachycardia ≠ Sepsis), test or even definition that gives anyone the answer to the question does this child have sepsis. 2016 saw the third meeting of the Society of Critical Care Medicine and the European Society of Intensive Care Medicine in an attempt to achieve a consensus definition of sepsis.  They will need to meet up again in 2018 if they are going to find true consensus about what sepsis is and what it looks like, since they couldn't quite decide the first three times.  Perhaps they just miss each other that much between conferences.
  • Sepsis doesn't appear, it develops.  There is a reason that we don't have an issue with clinicians missing a diagnosis of croup.  Croup announces its arrival most helpfully.  If only sepsis did the same.  
  • There is almost always another diagnosis to distract the clinician.  As mentioned above, before a child is diagnosable with sepsis, they usually have a prodromal illness.  A classic example of this is secondary sepsis in children with chickenpox.  It is completely understandable that when a child presents with fever and being miserable, having the typical chickenpox rash seems to make the diagnosis obvious.  However, some of these children have sepsis, and it is important to know when that is a strong possibility.
  • All of the features of sepsis are non-specific and can belong to another diagnosis.  Features such as tachycardia are frequently difficult to interpret as a fast heart rate may be due to pain, fear or pyrexia - all of which occur in children who do not have sepsis.  In any case, there is no definition of tachycardia, so we rely on guideline figures.  
  • You can't rely on any one feature to be present all of the time.  Even pyrexia may be absent.  Recognising severe sepsis is relatively easy, but we are being asked to recognise sepsis earlier, before it becomes severe.  That is much more of a challenge.

So, in summary, early sepsis is vague and it is easy to miss because it often hides behind a more obvious diagnosis.  The result is that guidelines are inherently too vague or too prescriptive when it comes to the recognition of sepsis.  Furthermore, if sepsis is not considered, the guideline is of no use whatsoever.

There is relatively simplistic way to deal with all of this.  Since the challenges are mainly about awareness and decision making, I think that a sepsis guideline could simply look like this:

Here are some footnotes on this:
  • Recognising the unwell child starts with recognising the well child.  All sorts of factors are taken into consideration.  While many guidelines emphasise physiological values (heart rate etc.), the behaviour and activity of a child are very important.  The gut feel assessment of the parent and the clinician are also valid.
  • The trajectory of the illness is not always treated with the importance that it deserves.  Children who are not septic often have periods of being subdued but then pick up and have a time where they look and behave as though they are much improved.  This is the "I can't believe how well my child looks now doctor!" effect.
  • Recognising sepsis comes with experience but any clinician can think about the possibility of sepsis.  If you are unsure, get a further assessment.

So, thinking about sepsis is the crucial first step.  It's the deciding that takes the most skill.  Then, when it comes to acting, we should be getting on with with doing whatever we need to do without unnecessary delay.  Hopefully that has made it sound a lot more simple than it really is.

Edward Snelson
Simple is what I need

Disclaimer - Simplification is a huge cop out for medical writers, but it's also a lot of fun.  Try it sometime.

Thursday, 18 May 2017

Ctrl F and Child Mental Health Problems - Making everything simple

Recently, someone showed me something that has changed my life.  If you press the Ctrl and F keys on your computer (Command +F for Apple) at the same time, a magic box pops up.  This is the 'find' function.  If you don't use it much, you should.  It makes a lot of things much easier.

Here's a non-medical example:  Let's say that you are looking for a payment that you know you made sometime 2-4 years ago from your bank account.  (I don't know, maybe the insurance company want to know how much you bought your laptop for.  Just go with the example please.)  You download the last five years of bank statement from the website and start trawling through for the money that you know that you paid to Amazon for the laptop.  Well stop that.  There is a much easier way.  Press the Ctrl and F keys and then type 'Amazon' in the box.  Hit enter and watch the magic begin.  Using this witchcraft you can find what you are looking for instantly.

Here's a medical example of how I use this function all the time.  Go to the NICE guideline for gastroenteritis in children.  Download the full guideline, not the summary.  Now read it until you find the evidence statement for how the guideline group formulated its decision regarding use of loperamide.  No, don't do that.  The document is over 200 pages long.  Instead use Ctrl and F to start your search, then move on using the arrows (or 'next') until you are where you want to be.

This little trick works for word documents, spreadsheets and anything else.  My favourite trick is to use it on a webpage to find something that I can’t see (like unsubscribe).  Since I was shown how to do this, it has made so many things much easier.  What is amazing to me is that not everyone knows about it.

I don't know what it is like in the rest of the world, but trying to help a child with a mental health problem in the UK can be a lot like trying to find something in a 200 page document.  Primary care clinicians can put a lot of work into trying to help children and young people (CYP) with mental health problems and it can feel like we never get anywhere.  Recently, a child psychiatrist told me a few things that helped to make a lot of sense of these problems and how to help CYP with them, including how to get your referral to the Child and Adolescent Mental Health Services (CAMHS) to get the most appropriate response.

What he told me all made perfect sense.  So I thought you might like to have me share his beautiful and simple insights into child and adolescent mental health problems.

1 - There are usually three factors which lead to children and young people's mental health problems

One of these factors is the child's genetic predisposition.  You can't do anything about that but it is still useful information.

The next factor is the child's environment.  Note that the weight of the domains of a child's environment change as they grow.  For example, the importance of different domains for a 4 year old might look like this:

Then as a child becomes more independent, the importance of each domains changes.
Of course, this is a gross oversimplification, which is exactly what I need in these kinds of circumstances.  By the time you reach adolescence, I suspect the weight that each domain holds over the young person varies greatly, but what the future holds (health, wealth and success or lack of) starts to become much more significant.

The third factor is a trigger.  This brings the intrinsic into contact with the extrinsic factors, precipitating the mental health problem.

2 – Every Child needs an anchor

Children and young people usually have at least one functional and dependable adult in their lives who they can rely on to give them consistency and who will make the CYP feel that they are worthwhile individuals.  A child who never has one of these people in their lives is unlikely to escape mental health disorders.  A child who loses their anchor is at high risk of developing a problem.   Ask, “Who is the most important person in this child’s life?”  If they used to rely on their grandmother who has recently died, this is very important information.

3 – Children and Young People get different mental health problems at different ages

It’s fairly obvious to say that but it does help you when it comes to assessing a problem.  When we are deciding whether something is a mental health problem in the first place, our first question should be, “Is what is happening normal for this age group?”

So what problems do CYP get at different stages?  They get mental health disorders which fit their stage of psychosocial development.  Young children tend to get behavioural problems and neurodevelopmental disorders (oppositional defiance disorder, attention deficit disorder, separation anxiety disorder).  Older children get problems that are related to their transition from child to adolescent (anxiety and self harming).   The top end of the CYP age group (in the UK this goes up to 18 years old) will get the beginnings of adult mental health disorders.

Knowing that something is abnormal doesn’t tell you how significant the problem is.  What tell you the answer to this is the same thing that almost always tells you about how significant a problem is in paediatrics: function.  So, the next question is, “How does this problem impact on the child’s ability to do the things that they want to do or should be able to do?”

And there you have it: your child psychiatry equivalent of the ‘find’ function.  A little understanding goes a long way when it comes to assessing and referring CYP with mental health problems.  Knowing what to ask always brings the best answers.  The answers to these questions just happen to be what a CAMHS consultant needs to see in a referral letter.  By including all of this information, we maximise that consultant’s ability to prioritise you patient.  Sound’s good eh?  So here they are again:

OK, so it’s hardly a keystroke, but considering that we are talking about one of the most complicated problems that we will see in our work, a five question model for getting what you need is pretty good going.

Edward Snelson
Impulsive clinician with a short attention span

Acknowledgement - Huge thanks to Girish Vaidya (@DrGirishPsych) who has helped me to understand the core principles of child mental health.  His ability to make the complex simple is a real gift.

Wednesday, 3 May 2017

If you don't like what you hear, change the tune. (What to do when you don't hear a wheeze in a child who should be wheezy)

Every now and then, a clinician will go to see a child who appears to have increased work of breathing and is well (in the way that children with viral induced wheeze usually are) but find no wheeze on auscultation.  How strange!

Making a diagnosis is a complex business.  It is such a complicated process that, most of the time, we don't really think about it at all.  This has been described as type 1 thinking (intuitive) in the context of clinical diagnosis. (1)  Most days, I do very little thinking.  When I come across something unexpected or unfamiliar, I am forced to come out of this unconscious automatic mode and think carefully and consciously (type 2 process) about what is going on.  I have to engage my cortex, and it hurts.

So, going back to this little scenario.  Let's say that the child is 2 years old and has has a cold for 3 days.  They are brought by his parents because they have noticed that his breathing is a little fast.  He looks well and is really quite happy with the toys in your room.  Snot bubbles from his nose as he comes and sits on his mother's knee.  Looking at his chest, he has mild subcostal recession and a mild tachypnoea.  When you listen to his chest, you hear...  breathing.

So, what most people do in this circumstance is to listen some more.  It is traditional to check your stethoscope for gremlins or signs of tampering before pushing the earbuds a bit harder into your ears before listening again.  However, there is no getting away from the fact that there is no wheeze, nor is this the silent chest that is so feared in asthma and viral wheeze.  In a silent chest, no breath sounds can be heard and the patient looks awful.  This child has breath sounds and looks well.

How strange.

The reason that it causes us to have a confused moment is that there are certain combinations of signs and symptoms that indicate a particular illness.  That is particularly useful in children's respiratory illnesses since no one sign or symptom is likely to be specific to an illness.  This is why cough and fever do not equal a lower respiratory tract infection.  We need to look for the presence or absence of other features to form a likely diagnosis.

So what we've got now is a mystery illness.  What causes a well child to have respiratory distress without a wheeze or stridor?
Your next move is simple.  Give the child inhaled (or nebulised if necessary) β-agonists.  I would go with 10 puffs of salbutamol via a spacer device.  Then sit back and watch the magic.

What will probably happen next is a little surprising the first time you experience it: a wheeze appears.  More importantly, the child's breathing improves.  So, what is going on here?

The answer to that would be science.  Science and music are happening and it goes like this:  In order to have a wheeze, there must be the correct conditions for this to occur.  A musical note needs the right amount of air flowing through a tube in the right sort of way.  The size of the tube matters quite a lot.  Ask any wind musician or organ player.

In these cases there is bronchospasm (caused by viral infection) but the conditions are not right to produce a wheeze for you to hear.  Of the parameters that affect the musical note (length of tube, diameter of tube and flow of air) you can change two with β-agonists.  You can't change the length of the tube but the other factors should respond nicely.

So, if you don't like what you hear, change the tune.  When your clinical diagnostic brain tells you that there should be a wheeze, you are probably correct.  If you were expecting a wheeze but don't hear one, by all means rethink your presumption.  If you are left with the same conclusion, then try the β-agonist trick.  It works a treat.

Edward Snelson

Disclaimer: This is a very different thing from rechecking a blood pressure until you get the number that you want.  Very different.   Anyway, I would never do that.

  1. Croskerry P, A universal model of diagnostic reasoning, Acad Med. 2009 Aug;84(8):1022-8.

Wednesday, 12 April 2017

Henoch Shonlein Purpura - Who, What, Where and When?

In Paediatric Emergency Medicine in the UK, it is often the case that a referral requires me to choose between more than one specialty.  For example cuts on the face (the ones that require suturing under general anaesthetic) could be referred to either plastic surgeons or maxillofacial surgeons.  Hand fractures are sometimes looked after by the orhopaedic surgeons (note use of their Sunday name) and sometimes by plastics.  Now that I think about it, the overlap almost always involves plastic surgery.

The decision about who to refer a patient to will depend on various factors.  These include resources, availability and the particulars of the case.  Matching the child and the illness (or injury) to the right person to follow the case up is part of the art of Primary Care.  After much thought and consideration, I've decided to refer children with Henoch Schonlein Purpura (HSP) to the very best.  I refer them to their General Practitioner.  
(Ankle bracelet not included.  See in store for more details)

The reason for this is that General Practice does two things better than any other specialty.  General Practice excels at avoiding the harm done by unnecessary tests and treatments, and (in my opinion) no other specialty in medicine is so good at providing the continuity needed to monitor a condition.  This allows the patient to receive appropriate care while at the same time having an experienced clinician involved who will intervene if needed.  For uncomplicated HSP, that is exactly what is needed.

HSP is the most common vasculitis in children.  Nobody really knows why children get it but the number one suspect is of course 'recent infection'.  These are always getting the blame for mysterious childhood illnesses.  If you ask me, I think it is institutional infectionism.

HSP is best known for causing a purpuric rash on the buttocks and lower limbs,  While this is the typical rash, atypical rashes are pretty common.  The thing that is most consistent about the HSP rash is the following triad:

HSP is a clinical diagnosis.  It is usually identifiable through a typical presentation and because other possible causes of non-blanching rash can be ruled out clinically.  Sepsis, leukaemia and immune thrombocytopaenia are some of the possibilities that should be considered if the presentation is not that of typical HSP, or if the child is unwell, or anaemic or has splenomegally (etc. etc.).

It is also worth mentioning that not all children have the courtesy to present with their symptoms in the correct order.  Everyone know that the rash should come first.  Some children choose to ignore this and complain of aches and pains before the rash appears.  Also, before the rash becomes purpuric it can start out as non-specific erythema or even look a little urticarial.

I am often asked if blood tests are needed for a child when diagnosing HSP.  My answer is this:  
For example, I don't do CRPs to diagnose sepsis.  I use a CRP once I have diagnosed sepsis because that will help in the ongoing management.  In injury, I use X-rays where it is probable that the X-ray will alter my management.  I don't use CXR to diagnose pneumonia.  I use CXR if I suspect complicated or atypical pneumonia.  In HSP diagnosis, tests are really for uncertainty in those cases where the presentation is ambiguous or atypical.  If the presentation is unambiguously HSP, no diagnostic tests are needed.  There are tests to be done but those are screening for complications.

Most cases of HSP follow a benign course.  The rash persists for several weeks and there many children experience aches and pains in their legs and abdomen.  However, symptoms other than the rash will typically settle in the first week or couple of weeks.  Things don't always go this way though.  There are four possible ways for the course of HSP to be problematic.

Problem 1) Extreme symptoms.

Pain is a funny thing and in some cases of HSP, despite a lack of significant complications, some children and young people get severe pain (despite good doses of simple analgesia) in their legs or abdomen.  These children should be referred acutely to be seen by a paediatrician.  This is both to enable management of the pain and to look for more significant complications.

Problem 2) Non-renal complications of HSP

I've said that leg and abdominal pains are fairly common symptoms of HSP.  It is also true that everything in paediatrics has an evil twin.  In the case of leg pains, it is possible for HSP to cause a significant polyarthritis.  If a child has swollen joints, the pain is severe or they develop a significant limp - refer.

Similarly, if a child with HSP shows signs of severe abdominal pain, consider the possibility that they have developed one of the most significant complications of HSP - intussusception.  Other signs might include pale episodes and blood or 'redcurrant jelly' in the stools.  With or without these other signs, assessment by a paediatric surgeon is urgently needed if abdominal pain becomes acutely severe.

Almost anything that can go wrong can go wrong in HSP.  Involvement of other organs than kidneys, skin, bowel and joints is rare.  Atypical symptoms such as headache or chest pain should be taken very seriously and the child should be referred acutely.

At some point, all of these factors will lead to a decision about where the child is managed.  I think that the decision usually looks like this:
There is nothing mandatory about referring a clear cut case of HSP at first presentation.  However, most GPs that I know would prefer an initial assessment in secondary care, even if the child is extremely well and has no symptoms with their non-blanching rash.

Problem 3) Renal complications

While aches and rashes are what cause children and parents to lose sleep over HSP, it is the possibility of renal complications that usually worries the clinician.   A significant chunk of children who have HSP will develop a mild nephritis.  A smaller number go onto get a significant nephritis and a small number develop severe, kidney-threatening nephropathy.  Don't worry too much about the numbers as they don't really help in a case series of one.  What is true is that it is very likely that the child in front of you will either never develop a renal problem, and if urine dip flags something up, it is most likely to be a transient mild haematuria or proteinuria.  In order to identify those cases of silent but significant nephritis, monitoring is needed for all cases of HSP.

Exactly how much monitoring is needed is slightly unclear.  Advice is based on clinical experience, common sense and a bit of logic.  If you put those things together, you might come up with this:
This is followup strategy is based on the well child, who has no significant haematuria or proteinuria at any point.

What this aims to do is detect renal involvement early, while avoiding any OCD type behaviour (such as daily urine dipsticks).  The length of follow-up is debatable but is based on a cohort study that showed that no child with HSP developed renal involvement after 6 months.  Roughly half the guidelines from big centres recommend follow up to 6 months and half say 12 months.

There are those that advocate longer followup (including lifelong annual reviews) for all cases.  However, I suspect that there is a significant effect of bias driving that.  If a child has had a complicated case of HSP, this may well be warranted, but if the course of the illness was benign I doubt that they will develop late complications.  The Nottingham renal unit recommends lifelong monitoring if everything else has been normal but there was at least one occasion where the urine dip showed ++ or more of protein. (1) This stratification allows for the possibility of nephropathy in selected cases rather than ongoing screening for all.

The need for a blood pressure check after the first couple of visits is also debatable (thus the *).  By continuing to check BP after it has been normal on two occasions, are we saying that the child could have had renal involvement severe enough to cause hypertension, yet this never showed up as a positive dipstick?  This seems very unlikely to me and I have never found a paediatrician who has seen such a thing happen.  Despite this, all guidelines and review articles that I have seen recommend that BP is checked at every visit.

Problem 4 - Prolonged or relapsing course of illness

This brings me neatly onto the final thing that might cause a clinician to feel that the child needs more investigation and management than can be given in Primary Care.  In some cases, the course of HSP does not follow the typical one of a few weeks of rash and a few days of other symptoms.  The symptoms might continue for months, or relapse after initial remission.  A mild relapse is actually quite a common occurrence in HSP and worth warning the family about.  If a relapse is severe or prolonged I would suggest that these children also need to be referred.  The paediatrician will need to review the diagnosis (in case the reason for an atypical course is that the diagnosis is wrong) and consider whether to investigate e.g. for an autoimmune cause of the rash.


Q. Does the child need blood tests at presentation?

A. Only if there is diagnostic ambiguity or if the urine dip/ BP is abnormal.

Q. Do steroids prevent complications?

A. No, but they may have a role in treating complications of HSP. (2) Other interventions that have found to be unhelpful include antiplatelet treatment or immunosupression.

Q. What counts as hypertension in a child?

A. This is difficult question to give a straight answer to.  It's not a lack of people coming up with definitions that is the issue.  It's more that we don't know much about what levels of hypertension cause what effect in the long term.  Most guidelines go for something like systolic BP >95th centile on three occasions.  It is important to use the correct size of BP cuff for the size of the child and to use an appropriate reference range. (3)

Q. So should I be checking BP at every visit even if the urine has been normal (no more than a trace of blood and no more than + protein) on every test?

A. If you didn't, you would be going against all the guidelines in existence.  I still haven't had a good explanation as to why it is really necessary, but nor have I convinced others that it is unnecessary, so for now you should keep on doing it.

So in summary, managing HSP is relatively straightforward.  After initial assessment, most can be monitored by their GP.  Some will need to stay under the care of a paediatrician and a small number will need to be referred on, usually to a nephrologist.  For the uncomplicated cases, there is no absolute certainty about often or how long to screen for renal involvement, so guidelines have to be mostly based on pragmatic expert opinion.

So, who, what, where and when?  Me, you and maybe them doing as much nothing as possible until we are sure that everything is OK.  Simple really.

Edward Snelson

I would like to express my deepest gratitude to the young person who consented to have photos of her HSP rash used for this purpose.  Thank you.

  1. Henoch-Schönlein Purpura (HSP) Guideline, Nottingham Children's Hospital
  2. W Chartapisak et al., Prevention and treatment of renal disease in Henoch-Schönlein purpura: a systematic review, ADC, Feb 2009
  3. Blood Pressure Levels for Boys by Age and Height Percentile, National Heart, Lung and Blood Institute

Tuesday, 28 March 2017

The Random Goldfish - When confirmation bias met affective bias

In the previous post, I explored how confirmation bias can lead us to believe that something is causing a problem when really it isn't.  Although sometimes unexpected, this kind of news is not unwelcome.  Finding out that fever doesn't really cause febrile convulsions is a surprise to many, but usually a good one.  Telling people that their treatments don't work is much less popular.

Anyone who has been a clinician for a reasonable amount of time knows what it feels like to share good and bad news with someone.  When I am teaching about paediatrics in primary care, it sometimes feels like I am saying that very few treatments actually work.  This feels having something taken away form us.  The real headline is that children make themselves better in the vast majority of clinical scenarios.  It is our job as clinicians to do as much nothing as possible while looking for opportunities to give effective treatments.

One question that I am often asked is, "If these treatments don't work, why do people use them?" Good question.  I tend to assume that my sample cohort of co-workers is representative of clinicians and I work with good, conscientious people who want to give children the best treatment possible. Since I don't believe that clinicians are generally unintelligent, malicious or lazy, I will take a risk and say that there must be powerful forces at work if any of us are giving ineffective medicines to children.  The problem that leads us all to use ineffective treatments is our very desire to make children better and parents happy.

If you want something really badly and do something in an attempt to make it come about, when the thing happens, we are likely to believe that this was cause and effect.  This approach would work in a fixed environment,  For example, consider a person trying to solve a puzzle (like a Rubik's Cube).  The puzzle isn't going to solve itself, so if the person tries many different strategies and then something works, they have solved the puzzle.  This assumes that the puzzle has not been solved by chance, which in this case is extremely unlikely.

Now consider someone with a different problem.  He wants a picture of his goldfish next to the castle in the goldfish bowl.  He tries shining a light to get the goldfish to move into position.  He tries tapping the glass, placing some food and tries making waves in the tank.  Whatever he does just before the goldfish moves into position must have done the trick right?  Wrong.

Well, much of paediatrics is like that.  Childhood symptoms often fluctuate or resolve.  We want our treatments to work.  We want to make children better and parents to be happy.  These factors are the perfect ingredients for us to wrongly believe that what we did worked.  Sometimes though, the goldfish just moves.  Because it's a goldfish.

Enough about goldfish. Let's use a really common example of how confirmation bias leads us and our patients to believe in an effect that is not real.

If I tell someone that antibiotics will cure a child's throat infection within a week, you can imagine how that sounds plausible.  Then, the initial belief in my statement will be reinforced when the child does indeed get better.  The true believer does not consider that the alternative is just as plausible - that all (uncomplicated) throat infections get better with time.  You know that guy who still has the viral sore throat he caught when he was two years old?  No?  Neither do I.

Paediatrics is a branch of medicine where most illnesses will resolve with time and many symptoms that could be attributed to a treatable cause.  But we and the parents both want the problem to be treatable.  The problem is, you're too nice.  You want to help and you want everyone to leave happy. This is called affective bias (the thing that reinforces confirmation bias). The end result is that we can easily believe that we are treating a problem, when in fact it gets better on its own.

Now, bias gets a bad name in medicine, but I would like to defend bias.  Clinicians could never learn or make decisions without bias.  We would be permanently uncertain and unable to choose. Without confirmation bias, we would never notice a pattern.  Without affective bias we would never take the parents seriously or care about the child.

Bias is good.  There, I've said it.

Bias is your friend, but friends can be fickle.  The thing about friends is that despite their faults, they're still your friends.  It is good to know what to expect from them.  That way, you don't feel surprised when they do the thing that they always do.  In the case of bias, your friend wants to mislead you and get you do do things you shouldn't do.

So, what are the best examples of the confirmation bias of presumed effect in paediatrics?  I've already mentioned antibiotics for upper respiratory tract infection.  There are many more, but lets just look at one in detail as an example:

Confirmation bias (presumed effect) - 
Example number 2: Treatments for gastro-oesophageal reflux disease in infants
If there was ever a paediatric condition that fitted the brief for this subject, it is feeding problems in babies.  The symptoms that babies present with are so often simply withing normal limits for infancy.   Did you know that straining is a thing that 1 in 6 babies do and that it is called dyschezia, not constipation?  If you add regurgitation of milk (aka 'reflux'), colic and other common gastrointestinal complaints, most babies have some sort of symptom that we could treat if we chose to during the first few months of life.  With a few exceptions, these are normal for being a baby, and will resolve in time.

The cardinal sign of a self resolving problem is that there are treatments available without good evidence of efficacy.  (Cough medicines for children are a good example of this.)  By way of contrast, there are very few treatment strategies for the management of pneumonia.  I'm guessing that you probably use antibiotics.

The evidence for the available treatments for reflux disease is not good.  In many cases the evidence is that they have little effect.  Rather than posting several dozen references, I am simply going to signpost you to the NICE guideline for Gastro-oesophageal reflux disease in children and young people. (1)  In the full document there is an extensive literature review which makes for interesting reading.  The bottom line is that the evidence is usually lacking.  The evidence that we do have form research points toward little or no effect for alginates, H2 agonists and PPIs.  By their own admission, much of the advice in the guideline depends on the experience of the experts involved in the guideline writing process.

Of course the problem is that there are infants with genuine pathology.  These children often begin their visits to healthcare professionals with non-specific presentations which easily fit the bill for what is 'normal for infancy'.  If we are honest with ourselves, the niggling doubt that the child might have a significant problem is one of the factors that pushes us in the direction of pulling out our prescription pads.  After all, it won't look as bad when the child turns out to have a problem later if we were busy trying treatments instead of reassuring the parent that these symptoms are usually part of normal infancy.

Avoiding unnecessary treatments is gold standard care.  Alginates are the most frequently used medications for reflux symptoms but in my experience this treatment runs a high risk of causing constipation.  This is far from ideal if you are trying to make life easier for baby and parent alike.   Motility drugs have repeatedly been associated with dangerous cardiac side effects and PPIs have been shown to increase the risk of respiratory tract infection. (2)  The take home message from this is that, although medication is an option, we need to be sure that a treatment is really likely to be better than watchful waiting.

The NICE guidelines focus on consideration of how the infant is affected - severe distress or red flags (faltering growth, feed refusal etc.).  It is also important to consider other possible diagnoses such as UTI.

I said that there were quite a few problems that have a similar story.  Going through all of them in detail would take a long time, but here is a list of some of the treatments that lend themselves to this combined bias effect:
The evidence for all of these treatments in children is that they work rarely (antibiotics for URTI, inhalers for cough alone, suspected CMPA based on colic alone) or never (cough syrups, simethicone or lactase for colic in babies).  All of these clinical scenarios share a common theme- the likelihood that the symptom will resolve in time.

So lets come back to bias.  Confirmation bias will cause us to believe that a treatment is effective while affective bias will make us want to give something even when there is little or no benefit. "But earlier, you said that bias is good.  You said that bias is my friend!" you might well say.  I stand by that.  As long as you know how you expect your friends to behave, any misbehavior can be managed and they can still be your friends.

For confirmation bias, we need to have good evidence to justify treatment that is used for symptoms when the natural course is resolution with time.  For example, I don't need evidence to back up my belief that morphine works for pain when a child has a broken leg.  If the child feels less pain afterwards, it has nothing to do with a goldfish effect.  Conversely, I should want evidence that a treatment is effective for any of the symptoms listed above.

For affective bias, we need to harness our desire to be nice to parents and children.  That means not wasting their time with ineffective treatments or worse still causing new problems. Sometimes, doing nothing is the nicest thing that you can do.  Managing to treat where appropriate and avoid unnecessary treatment is the holy grail of paediatrics.  Ultimately, the child is the patient and we need to only give them medication that is more likely to help than harm.  At least, that's what we should be trying to do despite our biases.

Edward Snelson
Amateur Medical Errorist

Disclaimer - I am too biased to be taken seriously, even by myself.

  1. NG1 - Guideline for Gastro-oesophageal reflux disease in children and young people, NICE
  2. Orenstein et al., Multicenter, double-blind, randomized, placebo-controlled trial assessing the efficacy and safety of proton pump inhibitor lansoprazole in infants with symptoms of gastroesophageal reflux disease, J Pediatr. 2009 Apr;154(4):514-520

Friday, 3 March 2017

Why has no one told me this before? Confirmation bias - It lies to you. It lies to everyone. What has it been telling you about children? (Part 1)

Recently, after I had explained why something was a medical myth, a colleague in Primary Care looked at me and with genuine exasperation said, "Why has no one told me this before?"

Good question.  The answer to this is complicated.  A lot of the time there is a big 'Emperor's New Clothes' factor.  Declaring a myth to be untrue requires someone to burst the bubble and it is not always the case that someone is listening or that anyone wants to change their belief.

Myths start for various reasons but only persist if they are fed.  For example, very few people actually believe in the existence of fairies.   Seeing a fairy or hearing from someone who claimed to see one might change that.   People do however believe that mice like cheese without any good evidence to support this.  Where does this belief come from?  Surely we can't all have taken Tom and Jerry cartoons at face value?  Since there was never any reason to doubt what we were told we continued to believe it. Well, it turns out that, whatever the basis for the belief, it is wrong when tested scientifically (Yes, this has been researched and published!).

The best ingredients for a myth are plausibility and confirmation.  Take the old chestnut about not being allowed to use adrenaline with anaesthetic in fingers as an example.  This myth originated when lidocaine and adrenaline were commonly mixed with various things to aid anaesthesia and asepsis.  The mix often contained cocaine, procaine and boric acid.  When skin necrosis developed in fingers, the cause was not isolated, but the idea that a vasoconstrictor (adrenaline) was the cause was credible.  In fact, the other ingredients were probably to blame.  Thus a myth  has persisted for roughly a century was created by a plausible theory and repeated episodes which seemed to confirm this theory. (1)

Confirmation bias comes in several forms.  It affects how we search for, interpret and retain information.  They have been responsible for misleading us about quite a few things in paediatics.  There are so many, in fact, that it would be ambitious to put them all in a single post.  Instead I will divide them roughly into two groups - those where we have been misled about cause and those where we are misled about effect.

  • We tend to consider what the cause of something is when we witness an event.  
  • We concentrate on an effect when we think we can influence events.

For now, I am going to run through some examples of presumed cause.  Lets start with the things that you may have been told are caused by something else, but probably are not.  It works like this:

Of course sometimes, the presumed cause is real.  We have confirmation bias for a reason and in most cases it is teaching us, not lying to us.  Assumption has a bad name for itself, but is a necessary part of how we work and learn.
(No disrespect to Mrs. Sullivan, who taught me that to assume makes and ass of you and me.  Mrs. Sullivan was an English teacher and the spelling mnemonic is valid even if the statement is completely wrong in the context of exploratory learning.)

In certain circumstances, the reality is very different from our assumptions.  This is usually due to a factor that is not as obvious as the two that we have associated.

There are several examples of this below.  The one that often surprises many people is finding out that it is a fallacy that fever causes febrile convulsions.  I know, right?  I mean it's in the name and everything!  It makes sense that fever causes febrile convulsions since a child develops a fever and then has a convulsion.  We even see a correlation between febrile convulsion and fever that comes on particularly quickly (or so we think).

The only problem is that the evidence goes against this being true.  When children are treated for their fever, it seems that they have the same number of fits.  (2) So what is the cause of the fits?  Probably badness.  Badness is the stuff that infections make which causes the fever, the flu symptoms and all that.  You know, chemicals and stuff.  So even when we treat the symptoms of the infection, badness still causes the seizure to occur.  We can't get rid of viral badness.  In most cases we just make children feel better until they make themselves well.

How does this change our practice?  When I found this out, it completely changed my approach to children who had suffered a febrile seizure.  I no longer worry that treatment needs to be focused on the fever rather than the child's wellness.  Most importantly, I now tell parents that the seizure was not preventable.  Often, the parent blames themselves for failing to treat the fever adequately.  They need to know that this convulsion was not their fault.

Next up is the apparent epidemic of allergy to amoxicillin.
We have to work this one backwards from the evidence.  Approximately 95% of children who have a label of amoxicillin allergy have no allergy when tested or challenged. (3) The explanation for this poor correlation is that children of a certain age frequntly develop a rash (which is often urticarial) while ill with a virus.  Viral and bacterial infections are difficult to tell apart, so it is not uncommon for a child to be given antibiotics while unwell with a viral illness.  When a culprit is sought for the rash, the antibiotics may be blamed, though the reality was that the virus caused it.

Finding this out completely changed my practice.  By careful case selection, I take every opportunity to undiagnose penicillin allergy.

Next up: another much maligned medicine - Ibuprofen.   Ibuprofen is often avoided in children who have history of wheeze.  I suspect that this is one of the biggest cases of (wrongly) presumed cause currently in paediatric practice.  You may have been told that ibuprofen causes wheeze or that ibuprofen should be avoided in children with a history of wheeze.  Well, it turns out that this is another myth that has persists despite being disproved.

Once again, the association in space and time of the medicine and the symptoms leads to a very rational fear that it is the ibuprofen causing the wheeze.  When large groups are studied, it seems that Ibuprofen may even be protective against wheeze. (4)  I'll just leave that one with you for a minute...

So after that bomb shell, something a little more palatable but still interesting.  Growing pains are not caused by (wait for it........) growing.  In fact no one knows what causes children to have growing pains.
Feel free to file this under 'how does that change my practice?'  I just think that it is interesting that we feel the need to have an explanation for a symptom which has no known cause and no effective treatment - a bit like colic really!

Next up is something a bit more meaty.  Based on the sessions that I do for GPs here and there, I would approximate that roughly three quarters of primary care clinicians are aware that there is a concern about using ibuprofen for children with chickenpox.  I also know that the basis for this concern is poorly understood.

The truth is that this concern was raised based on a cluster of cases of children who developed severe complications of secondary infection about 20 years ago (5).  No causal link has ever been convincingly shown and the fact that huge numbers of children continue to have ibuprofen in this context makes me think that more robust evidence would have emerged if there was genuine cause and effect.

Invasive streptococcal infection during varicella infection is something that all clinicians should know about.  It is also true that most children who have chickenpox are not very unwell and so paracetamol should be all that is needed.

So why does this matter?  It matters when someone is blamed for something based on poor evidence.  So, let's be clear.  The Emperor appears to be naked, but if anyone else can see that he's got clothes on, I am prepared to be convinced.

Edward Snelson
Non-steroidal guardian of the year 2014-2016

Disclaimer- I would never use any of the treatments listed above.  For many years now I have only used fairy magic to treat my patients and any prescribed medication is a pretence.  No one can prove to me that fairies don't exist. 

  1. Bradon et al, Do Not Use Epinephrine in Digital Blocks: Myth or Truth?, Plastic & Reconstructive Surgery, February 2001
  2. A Sahib El-Radhi, W Barry, Do antipyretics prevent febrile convulsions?, ADC, Volume 88, Issue 7, 2003
  3. Caubet JC et al., The role of penicillin in benign skin rashes in childhood: a prospective study based on drug rechallenge, J Allergy Clin Immunol. 2011 Jan;127(1):218-22.
  4. Kanabar et al., A review of ibuprofen and acetaminophen use in febrile children and the occurrence of asthma-related symptoms, Clinical Therapeutics, Volume 29, Issue 12, December 2007, Pages 2716-2723
  5. Zerr DM. et al., A case-control study of necrotizing fasciitis during primary varicella, Pediatrics. 1999 Apr;103(4 Pt 1):783-90.