Hyperekplexia in a girl with posterior fossa malformations.

Hyperekplexia is a rare clinical syndrome of pathologic startle response to unexpected stimuli such as sound or touch. The majority of cases are familial. Sporadic cases of hyperekplexia have also been reported, mostly in association with brainstem pathology. We describe a girl with sporadic hyperekplexia secondary to previously unreported cerebellar pathology. Her symptomatology was predominantly unilateral, being ipsilateral to the cerebellar involvement. This type of presentation, which may be termed hemihyperekplexia, has not been described before. Response to clonazepam was good but showed diurnal variations. The case is being reported for its unusual features.