A 57-year-old man presented acutely with involuntary movements of his left hand. He had hypertension, chronic kidney disease and chronic obstructive pulmonary disease. These movements were best described as sudden, recurrent and arrhythmic loss of tone and power of the left wrist and fingers (video 1). They were most prominent when extending the left wrist, but were absent when the arms were at rest and were not elsewhere. There were no additional neurological deficits. Serum urea, ammonia, sodium, potassium, calcium, magnesium, phosphate …