A fit and healthy 48-year-old farm mechanic from Yorkshire gradually developed unsteadiness over 24 h associated with nausea, vomiting and malaise. The next day he developed a dull occipital headache and his unsteadiness worsened. His symptoms progressed over the next 48 h with slurring of speech, diplopia, rotational vertigo and intractable hiccups. He did not seek medical attention until day 4 when he woke with right-sided weakness and pareasthesia.

On arrival at the accident and emergency department, he was afebrile, mildly dysarthric and had an ataxic gait. MRI of the brain showed abnormal high T2 signal within the brainstem (figure 1). Treatment with dexamethasone was commenced, but his symptoms worsened after 48 h …