Objective: We describe a case of MMD in which the patient presented with negative myoclonus.

Background: Moyamoya disease (MMD) is a progressive cerebrovascular disorder characterized by occlusion of the terminal portions of the internal carotid arteries. The clinical manifestations of MMD present with various neurological symptoms, most commonly stroke. However, in rare cases, MMD may present as a movement disorder.

Method: A 42-year-old man presented with intermittent involuntary movements several months ago. These neurologic symptoms were triggered by tension or excitement. Distinct involuntary movements were not observed during the outpatient clinic, and other neurological abnormalities were normal. However, a personal video recorded by the patient revealed negative myoclonus in both upper extremities. There was no familial history of similar symptoms.

Results: Brain magnetic resonance (MR) imaging showed diffuse, irregular, and prominent leptomeningeal enhancement (right > left) on the gadolinium-enhanced T1-weighted image referred to as “ivy signs”. Brain MR angiography demonstrated near-total occlusions of both distal internal carotid arteries to middle cerebral arteries (MCA, right > left), with the posterior cerebral artery also involved, along with supplementary abnormal vessels. Perfusion MR demonstrated widely prolonged mean transit time in both hemispheres. Electroencephalography showed normal findings. Genetic analysis identified a pathogenic RNF213 gene variation: NM_001256071.1: c.14429G>A (p.Arg4810Lys). Other laboratory tests for vasculitis were normal. The patient was diagnosed with MMD and underwent a right superficial temporal artery-MCA bypass surgery.

Conclusion: In this case, it is critical not to overlook MMD during the initial diagnosis. Therefore, if a patient presents with unexplained movement disorders, it is important to clearly assess the symptoms through methods such as personal videos and perform brain imaging to make an accurate diagnosis. Specifically, contrast-enhanced brain imaging are crucial for identifying any abnormalities in the cerebral vessels.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/uncommon-presentation-of-moyamoya-disease-mmd-a-case-of-negative-myoclonus/