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Myoclonus is a sudden, brief, involuntary muscle jerk, sufficient to cause movement. Cortical myoclonus is well recognised and characterises many neurological diseases1 Myoclonus can be classified by presumed cause or anatomical origin. Peripherally generated myoclonus is not well characterised, with the exception of hemifacial spasm (HFS).
A 71-year-old woman awoke with a twitching of her right hand, which persisted despite distraction, sleep or voluntary use of the hand. The ‘twitch’ comprised a single complex movement, involving contraction of abductor digiti minimi (ADM) and flexor carpi ulnaris (FCU) muscles. It was rhythmic (approximately 1 Hz). There was no antecedent trauma to the hand, and no past medical or family history of neurological disease. Medical history included schistosomiasis infection (1960s), ductal carcinoma in-situ of the left breast(1999), and splenectomy following ruptured splenic aneurysm (2009). She took omeprazole 20 mg, aspirin 75 mg, amlodipine 5 mg, penicillin V 500 mg daily. Examination 4 days after onset revealed no other abnormalities and no motor or sensory deficit in the hand.
Blood count and routine biochemistry were normal. Anti-neuronal antibodies and anti-voltage-gated potassium channel antibodies were negative. MRI of brain, spinal cord, brachial plexus and arm to below the elbow were unremarkable.
Median somatosensory evoked potentials (SEPs) and EEG were normal with no EEG correlates related to the hand movements; 2 mg …