Teaching Video NeuroImages: Slow periodic myoclonus in subacute sclerosing panencephalitis and fulminant Wilson disease

Slow periodic myoclonus is a well-recognized phenotype of fulminant subacute sclerosing panencephalitis (video 1).¹ This distinctive phenotype has not been previously recognized in another rapidly progressive disorder, fulminant Wilson disease. We documented slow periodic myoclonus in a 34-year-old Peruvian man who developed paranoid schizophrenia and, 6 months later, levodopa-unresponsive parkinsonism and falls, progressing into akinetic mutism (video 2). Prior to death, the diagnosis of Wilson disease was supported by ocular and neuroimaging features (figure), low ceruloplasmin (5.3 U/L), high urinary copper, and diffuse hepatopathy on echography. Slow periodic flexor myoclonus reflects cortical excitability and bears a poor prognosis.² The EEG correlates are generalized, high-amplitude, quasiperiodic complexes.

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