Unilateral symptomatic palatal myoclonus: MRI evidence of contralateral inferior olivary lesion.

Symptomatic palatal myoclonus is a rare syndrome of segmental myoclonus which is thought to occur after damage to certain brainstem or cerebellar structures. We report two patients with unilateral PM, who showed hypertrophy of the inferior olivary nucleus on magnetic resonance imaging. In the first patient this was due to a left pontine tegmental hemorrhage, and a right-sided oculo-palato-facial myoclonus developed one month after the episode. The second one had a basilar artery occlusion with ischemic infarcts at the basis pontis, dorso-lateral aspects of the left pons, and left cerebellar dentate nucleus, as well as the occipital lobe. A delayed left oculopalatal myoclonus was recognized 3 months later. Interruption of the "dentato-rubro-olivary pathway" by the lesion with ensuing neuronal loss, cytoplasmic vacuolation, and astrocytic proliferation in the inferior olive, together with an increase of water content as mobile proton may cause the MR signal abnormalities in patients with unilateral symptomatic palatal myoclonus.