A case of congenital hypoplasia of the left cerebellar hemisphere and ipsilateral cortical myoclonus

We describe a case of a 32-year-old woman presenting with intermittent jerks, limited to the left upper limb, starting at age 15. After some years the jerks became constant, present at rest and worse during action and spread to the left leg. They remained stable after age 21. The patient had normal birth and reached all developmental milestones on target. She tended to walk pigeon-toed, and she was clumsy as a child; despite this, she used to play netball at school. Her family history was unremarkable. On examination she had distal, positive, arrhythmic jerks involving the left upper and lower limbs, present intermittently at rest and exacerbated by action and tactile stimuli. Our clinical impression was that of unilateral cortical myoclonus (CM). There was no personal and family history suggesting secondary causes of CM. The electroencephalogram was normal, and brain magnetic resonance imaging was compatible with congenital hypoplasia of the left cerebellar hemisphere, including mild dysplastic features. The magnetic resonance imaging appearance has not changed in 10 years. A combination of clonazepam (1 mg/day) and valproate (600 mg/day) was effective in controlling the jerks, with subjective improvement of 60%.