Hemitonic seizures: etiological and diagnostic considerations.

Intermittent unilateral tonic posturing of the limbs may relate to focal motor epilepsy, intermittent dystonia or hysteria, and diagnosis may be difficult. Five patients are presented who illustrate two distinct hemitonic syndromes which we believe to be epileptic, namely forced elevation of one arm and paroxysmal hemispasm. It is suggested that these attacks follow an irritative lesion involving the supplementary motor cortex and a deep lesion involving striatothalamic projections respectively. Brevity of episodes, their stereotyped nature and rapid response to anticonvulsant drugs supports an epileptic etiology. The term paroxysmal hemidystonia may not be appropriate for patients with intermittent stereotyped disorders of limb posture, where the clinical features support an epileptic basis and we suggest the designation hemitonic seizures.