16th August 2024

A 42-year-old man with Crohn’s disease on natalizumab and prednisolone is reviewed in the urgent neurology clinic

A 42-year-old man with Crohn’s disease on natalizumab and prednisolone is reviewed in the urgent neurology clinic. His referral letter notes a progressive confusion and lethargy over the preceding 3 months, with an ataxic gait and right arm weakness emerging in the last few weeks. He was seen in the Emergency Department following a short, self-terminating generalised seizure 2 weeks ago.

His observations are within normal limits.

Urgent imaging of the brain is arranged. The MRI demonstrates asymmetric, confluent white matter lesions bilaterally, without contrast enhancement or mass effect. Rapid HIV testing is negative.

Which is the single most likely diagnosis?

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