Cortical myoclonus and cerebellar pathology

Objective To study the electrophysiologic and pathologic findings in three patients with cortical myoclonus. In two patients the myoclonic ataxic synd rome was associated with proven celiac disease. Background: The pathologic findings in conditions associated with cortical myoclonus commonly involve the cerebellar system, but there has only been one report of cerebellar pat hology in a patient in whom cortical myoclonus was physiologically characte rized antemortem. Methods: Cortical somatosensory evoked potentials (SEPs) were recorded and EEG activity was averaged preceding myoclonic electromyog raphic activity. In one patient cortico-cortical inhibition was tested usin g two paired ipsilateral magnetic stimuli over the motor strip. Neuropathol ogic examination was carried out, including linear Purkinje cell densities/ millimeter calculations for different regions of the cerebellum. Results: T he electrophysiology showed evidence of dysfunction of the sensorimotor cor tex with enlarged SEPs and a time-locked cortical potential preceding the a ction myoclonus. In addition, motor cortical inhibition was abnormal in one case. Pathology showed unremarkable primary sensory, motor, and premotor c erebral cortices, except For unilateral gliosis of the motor cortex in one case. The cerebellum showed patchy atrophy and ongoing degeneration. A stri king feature was the greater severity of Purkinje cell loss and Bergmann gl iosis in the outer aspects than in the depths of the folia. Conclusions: pa thologic abnormalities are paradoxically mainly located in the cerebellum i n some patients with cortical myoclonus, despite clear electrophysiologic e vidence of cortical dysfunction. This observation suggests that enhanced ex citability of the sensorimotor cortex may arise as a distant effect of cere bellar pathology.