MRCP2-3200

MRCP2-3200

A 59-year-old man presents to the neurology clinic with a history of increasing bilateral hand weakness and clumsiness over several months, with the right hand being worse than the left. He reports difficulty with writing, fine manipulation, and poor hand grip. He denies any sensory disturbance or neck problems but has recently developed weakness in his right knee. His medical history includes hypertension and hypercholesterolemia, and he takes bendroflumethiazide and simvastatin regularly. He smokes 20 cigarettes per day and drinks 10 units of alcohol per week. On examination, there is bilateral hand and forearm wasting with absent clawing or fasciculations, and reduced muscle bulk of the proximal musculature. Shoulder abduction/adduction is 3/5, and there is marked distal weakness affecting wrist and finger flexors of 2/5. Sensation is intact. Investigations reveal a fasting plasma glucose of 8.5 mmol/L, and a lumbar puncture shows an opening pressure of 10 cmH2O, CSF protein of 0.35 g/L, and CSF white cell count of 4 cells per ml. Which investigation is most likely to confirm the diagnosis?