28th May 2025

A 70-year-old man is admitted to hospital with sudden onset of right leg weakness.

A 70-year-old man is admitted to hospital with sudden onset of right leg weakness. His past medical history includes chronic back pain, hypertension and hypercholesterolaemia. On examination, he has weakness of his right hip flexion and extension, knee flexion and extension and ankle dorsiflexion. Sensation to light touch and pinprick is intact. He has a brisk knee and ankle reflex and an upgoing plantar on the right. He undergoes a CT brain which is reported as normal, and then an MRI of his spine, which shows degenerative changes only.

Which of the following options is the correct diagnosis?