Acetazolamide-responsive hereditary paroxysmal ataxia: report of a new family.

Five family members were examined because of occurrence since childhood of recurrent episodes characterized by vertigo, dysarthria and gait ataxia. Analysis of the pedigree was consistent with an autosomal dominant mode of inheritance. Though asymptomatic between attacks, all the patients presented on examination a gaze-evoked and rebound nystagmus associated with a saccadic pursuit, a deficient optokinetic response and an inability to suppress the horizontal oculo-vestibular reflex by fixation; hypermetric saccades and truncal ataxia were also present in most of them. A sixth family member, aged 6 years, was found to present a gaze-evoked nystagmus but was completely asymptomatic. Response of the attacks to acetazolamide therapy (250 mg twice a day) was assessed in two patients and was either partial or complete. A positron emission tomography (PET) study was realized between ataxic spells in one patient and demonstrated a decrease of glucose metabolism in the whole cerebellum, the inferior part of the temporal lobes and the thalami. These PET data as well as the detailed neuro-ophthalmological findings bring new informations about acetazolamide-responsive hereditary paroxysmal ataxia, a rare but probably often misdiagnosed and treatable disorder.