16th August 2024

A 74-year-old man is seen in Ambulatory Care with his wife, having been referred by his GP with a general decline and headache

A 74-year-old man is seen in Ambulatory Care with his wife, having been referred by his GP with a general decline and headache. He reports that he has been less able to get around the house as he feels that his left leg has been weaker than usual. This has been getting progressively worse over the preceding 3 months, to the point where he now spends most of his day in a chair, compared to walking 4 miles daily several months ago. He also reports headaches and fatigue. His wife reports that he has occasionally been confused, which is out of character for him.

He had previously been fit and well, taking only amlodipine 5 mg for hypertension, which is well controlled.

On examination, he appears frail. General systems examination is unremarkable. Neurological examination reveals weakness in the left lower limb, worse in the flexors, with a slightly increased tone and brisk deep tendon reflexes. There is barely perceptible weakness of the left upper limb.

Which is the single most definitive next investigation?

Select the SINGLE most appropriate option from the list below. Select ONE option only.