"Cortical" Wrist Drop due to a Cerebral Peduncle Infarct.

Wrist drops are usually due to a peripheral neuropathy affecting the radial nerve. Cortical wrist drops may occur, usually due to a lesion in the contralateral hand area of the motor cortex. We report a unique case of "cortical" wrist drop due to an acute infarction of the contralateral cerebral peduncle. The patient is a 70-year-old gentleman with the vascular factors of hypertension, hyperlipidaemia, and prior cerebellar strokes, who developed sudden onset of right wrist weakness without numbness. Neurological examination showed a right wrist and finger drop. Nerve conduction study of the radial nerve was normal. MRI brain revealed an acute infarct in the medial part of the left cerebral peduncle, extending slightly to the medial thalamus; there were also old medial posterior cerebellar infarcts. Time of flight MR angiography was normal, with hypoplastic right vertebral artery. Echocardiography was normal but for a dilated right atrium. Electrocardiogram was normal, and 24-hour Holter monitoring detected infrequent atrial and ventricular ectopics. X-ray wrist showed an old ulnar styloid fracture. Nerve conduction study of the radial nerve was normal. He was switched from aspirin to clopidogrel and underwent rehabilitation. The cerebral peduncle should not be forgotten when attempting to anatomically localise the site of the lesion when evaluating a patient with a wrist drop.