Wednesday, 21 October 2015

It's all about the wave - An expert's tip for recognising seizures in children

I was recently picking the brains of a paediatric neurology colleague and discussing how they distinguished epileptic seizures from other events.  I already knew that it wasn't through the black arts of EEG (electroencephalogram) interpretation.  I'm sorry to be the bearer of bad news but EEG has a very poor sensitivity and specificity for epilepsy (1).  By the time an EEG is requested, a diagnosis should already have been made on clinical grounds.  The EEG is then useful as part of deciding how to manage the epilepsy, not to screen for epilepsy.


Why do we front line clinicians need to be able to tell the difference?  There are so many things that children present with that could be seizures but probably are not.  One good example of this is absence seizures.

Absence seizures (no longer called petit mal) account for 10% of epilepsy in children.  The incidence of epilepsy in childhood is not well described but is probably about 1/2000 making absence seizures about 1/20,000.  Staring episodes are very common in children and if these occur frequently, it is understandable that parents or teachers want to know if this is a form of epilepsy.  Not all of these need to be referred.

If a paediatric neurologist makes the diagnosis from the history, then so can any clinician.  All we need is to know what their secret is.  It turns out that they are riding a wave.

The characteristic feature of absence seizure is the abrupt and brief impairment of consciousness with a complete inability to intrude on the episodes.  (2) What this means to the observer is that they will notice a sudden onset and then notice the event suddenly finish.

 Fig 1. If you were to plot the change over time, an inattentive staring episode would be like a sine wave.
Fig 2. The typical abrupt onset and cessation of an absence seizure gives a square wave.

It may just be that simple.

Of course, I am not suggesting that no examination is needed.  There are also other features of absence seizures that may be helpful:
  • The episodes occur during any activity and in any environment
  • There may be subtle muscle twitches or lip smacking (automations)
  • There may be a slight loss of tone leading to slumping of the head or trunk

There are two ways that you can get to see the episodes for yourself.  If they happen frequently then, through the magic of smartphones the parents will be able to capture an episode for you.  There is a better way though, as almost all absence seizures can be provoked through hyperventilation as demonstrated beautifully in this video:

So, I have to give thanks to Tony for telling me about the wave thing.  I find pictures are a great way to help me understand things that I know, when I don't necessarily know them well enough.

Edward Snelson
Wave junky
@sailordoctor

References
  1. EEG in the diagnosis, classification, and management of patients with epilepsy, S J M Smith, J Neurol Neurosurg Psychiatry 76:ii2-ii7 doi:10.1136/jnnp.2005.069245
  2. Typical absence seizures and their treatment, C P Panayiotopoulos, Arch Dis Child 81:351-355 doi:10.1136/adc.81.4.351




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