A case of hemichorea in RNF213-related vasculopathy.

BACKGROUND Internal carotid artery (ICA) stenosis has been recently reported to cause hemichorea, mainly in East Asia. The East Asian-specific p.R4810K variant of RNF213, a susceptibility gene for moyamoya disease (MMD), accounts for up to 25% of sporadic ischemic stroke with ICA stenosis cases in East Asia. However, as RNF213-related vasculopathy does not meet the diagnostic criteria for MMD, the creation of a new disease category has been suggested. Here, we report the first case of hemichorea in RNF213-related vasculopathy. CASE PRESENTATION An 81-year-old woman was admitted to our hospital with choreic movements in the periphery of the right extremities at rest. Though head magnetic resonance imaging showed no fresh or old cerebral infarction, 123I-iodoamphetamine-single photon emission computed tomography showed cerebral blood flow of < 80% in the anterior territory of the left middle cerebral artery (MCA) in a resting state and cerebrovascular reactivity of < 10% in the broader area supplied by the left MCA after acetazolamide challenge. Head magnetic resonance angiography and digital subtraction angiography revealed left ICA C1 portion stenosis with compromised collateral vessels. Involuntary movements resolved with haloperidol administration within 3 days, without apparent recurrence from continuation of the medication for a year. Genetic testing revealed the presence of the heterozygous RNF213 p.R4810K variant. CONCLUSIONS Chorea is thought to be caused by damage to circuitry connecting the basal ganglia with the cerebral cortex, as found in cases of MMD, which possess aberrant vessels in the basal ganglia. However, aberrant vessels and cerebral infarctions were not observed in the basal ganglia in the current case, decreasing the likelihood of a role in chorea. Alternatively, as RNF213 regulates vascular endothelial function and angiogenesis, dysregulation may impair the neurovascular unit and damage basal ganglia circuitry, contributing to the development of chorea. This case may renew interest in the concept of RNF213-related vasculopathy and the pathophysiological mechanisms behind chorea in ICA stenosis.