Many of us have been taught to consider a personal or family history of atopy when making certain diagnoses in children. Although it might seem like this is an important factor, the logic for including the history of atopy has several flaws. It is notable that some guidelines are de-emphasising the value of such factors when considering a diagnosis of another atopic condition.
The first thing that is wrong with the use of the family history of atopy is that it is often itself wrong. We know that many diagnoses of asthma in children turn out to be wrong and that people can misinterpret what they were told. Were they given a diagnosis of asthma or were they told that their symptoms could possibly be due to asthma. Many patients don't understand what a maybe diagnosis is, no matter how comfortable we are with the concept. Similarly, there is much overdiagnosis of allergy, especially antibiotic allergy. The end result of all this is that there are many people with a history of an atopic condition but who never had that condition.
It is also worth factoring in that (depending on which study you read) there is a significant possibility that the stated father is not the biological father. It's not a major factor, but if we're going to consider odds, it is a factor.
The most important argument for me is to do with the way that the diagnosis is made. The question is, do you rely on something in the history in order to make a diagnosis? For example, a child presents with a fever and no clear focus. They have never left the UK in their life, so that pretty much rules out malaria.
Conversely, a ten year old child presents with a history of recurrent wheeze. This seems to have multiple triggers and is no just related to viral infections. The wheeze responds well to inhaled salbutamol. The child has never had eczema and neither parent has any history of any atopic conditions. Well that rules out asthma then doesn't it? Of course not.
The idea that a personal or family history of atopy should be a deciding factor may well be responsible for much of the overdiagnosis of certain conditions. For example, a three year old presents with four episodes of wheeze in the space of a few weeks. Each episode has been preceded by a runny nose and each has resolved over the course of a few days, with only a salbutamol inhaler for symptomatic treatment. The child's parent asks if the child has asthma. Both parents were given a diagnosis of asthma in childhood. Also, this child had eczema as a baby.
Already I can feel the gravitational pull of the asthma diagnosis. The personal and family history of atopy feel like compelling evidence, especially if we are slightly unsure about a diagnosis. However, it doesn't change the fact that the clinical picture is one of viral wheeze and not asthma. For this reason, the British Thoracic Society guidelines have de-emphasised the importance of the family history of atopy in diagnosing asthma in children. "The diagnosis of asthma in children and adults is based on the recognition of a characteristic pattern of respiratory symptoms, signs and test results and the absence of any alternative explanation for these." (1)
When it comes to uncertain diagnoses, we are rarely more unsure of ourselves than when considering a diagnosis of non-IgE cow' milk protein allergy (CMPA). It doesn't help that there is no test that we can rely on or that the symptoms are all non-specific. CMPA, more than most diagnoses, relies very much on the recognition of a best-fit. Often and quite rightly, it is a diagnosis which is considered after other more likely diagnoses have been initially presumed. Should the infant having eczema or a parent with a history of atopy influence that process?
What you really want to know now of course is the increase in statistical probability of CMPA which is associated with eczema and family history of atopy. I don't know the answer to that. If you know, keep it to yourself. Never tell me the odds.
Disclaimer - Han Solo's death is in no way proof that you should know the odds. His long and successful career is proof enough that reckless and uninformed decision making is the best way to go about things.
- British guideline on the management of asthma, British Thoracic Society & Scottish Intercollegiate Guidelines Network