The correct answer is C. The history given above is a classic presentation of acute post-infectious cerebellar ataxia. 25% of children with this disorder have a history of varicella infection within 1 month prior to the onset of the disorder and 5% of children have a previous history of varicella vaccination. The onset of acute cerebellar ataxia is usually explosive, often with the child awakening from sleep with maximal symptoms of ataxia and nystagmus. In any child with acute ataxia, it is important to obtain a drug screen and a careful history of any possible toxic exposures since poisoning and acute cerebellar ataxia account for most of the cases of acute ataxia in children. Resolution of the symptoms occurs in most children over a period of weeks to months.
Concomitant diarrhea (choice A) is not relevant to this presentation. Although there are forms of Guillain-Barre syndrome that have ataxia as a prominent component, this child does not have the other symptoms associated with these variants of GBS (ophthalmoplegia, depressed reflexes), and Campylobacter diarrhea usually precedes the onset of GBS.
While an intracranial tumor is always of concern in a child with neurologic symptoms, the history above is atypical for tumors, which usually present more indolently. The history of a cousin with a brain tumor does not increase the likelihood that this child's symptoms are due to an intracranial mass (choice B).
Pseudoataxia (choice D) is a syndrome of recurrent bouts of ataxia that are actually atypical seizures on EEG. The attacks are similar in timing to seizures and there may be a postictal state. They are not likely to persist over days as in this child.
Recent streptococcal pharyngitis (choice E) is of importance in movement disorders associated with acute rheumatic fever, such as Sydenham chorea, but does not predispose to any known form of ataxia.
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