Objective: To give a thorough neurophysiological description of a patient presenting with unilateral cortical myoclonus and homolateral congenital cerebellar hemiatrophy

Background: The role of the cerebellum if the pathophysiology of cortical myoclonus has been previously proposed, assuming that a lack of cerebellar inhibitory control would increase the excitability of the contralateral sensorimotor areas. However, direct evidence to support this hypothesis is still absent.

Methods: We examined a 32-year old female presenting with isolated atrophy of the left cerebellar hemisphere and stimulus-sensitive myoclonus involving the left upper and lower limb. Neurophysiological investigations included short intracortical inhibition (SICI), cortico-muscular coherence (CM), somatosensory evoked potentials (SEP), long-latency reflexes (LLR), short-latency afferent inhibition (SAI), long intracortical inhibition (LICI) and transcranial evoked potentials (TEP) obtained by magnetic stimulation of the primary somatosensory cortex. All tests were performed bilaterally.

Results: SEP were bilaterally large, with a small prevalence of the right hemisphere, although not frankly giant. CM and SICI were not different between the two sides. LLR recording showed a clear C reflex, larger on the left hand compared to the right (1.67 vs 0.56 mV). TEP showed a prominent and widespread early negative component, peaking around 20 ms, again larger on the right hemisphere. Both LICI and SAI obtained by stimulation of the right motor cortex were impaired, showing only around 10% and 37% inhibition respectively.

Conclusions: The present results suggest an imbalance in several neurophysiological measures of cortical excitability and, taken together, offer evidence about a possible involvement of the cerebellum in the pathogenesis of cortical myoclonus.

References: 1. The role of the cerebellum in the pathogenesis of cortical myoclonus. Ganos C, Kassavetis P, Erro R, Edwards MJ, Rothwell J, Bhatia KP. Mov Disord. 2014 Apr;29(4):437-43. doi: 10.1002/mds.25867. Epub 2014 Mar 14.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/cortical-myoclonus-explained-by-cerebellar-dysfunction-evidence-from-a-unique-case/