A number of medications have been used with varying success to treat the symptoms of generalized, focal, and paroxysmal dyskinesias; these agents include anticonvulsant, benzodiazepine, neuroleptic, dopaminergic, dopamine antagonist, and carbonic anhydrase inhibitor types. The carbonic anhydrase inhibitor drug group is best represented by acetazolamide, which has been widely applied in the treatment of paroxysmal dyskinesias. Zonisamide, which has several putative pharmacologic mechanisms of action, is a member of the carbonic anhydrase inhibitor drug group. Zonisamide was chosen for treatment of secondary paroxysmal dystonia in a patient with pyruvate dehydrogenase deficiency (case 1) and in two patients with neonatal hemochromatosis and family history of neonatal hemochromatosis (cases 2 and 3). Although zonisamide ameliorated the symptoms of secondary paroxysmal dystonia in these three patients, the precise biochemical mechanism remains unclear, and further studies are needed to substantiate and explain this finding.
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