MRCP2-3125
A 50-year-old man presents to his GP with a complaint of episodic vertigo that has been occurring for the past two weeks. He reports that the vertigo is particularly noticeable at night when he is trying to turn over in bed. He denies any history of nausea, vomiting, tinnitus, hearing problems, diplopia, or limb weakness. He recently had a cold and has been feeling under the weather in the last week, but otherwise has no other symptoms. He has a past medical history of epilepsy and takes regular carbamazepine. He is a non-smoker and drinks eight units of alcohol per week.
On examination, his vital signs are normal. The external auditory canal and tympanic membrane appear intact in both ears. Cranial nerve examination reveals asymmetric horizontal nystagmus with a rotational component, but ocular movements and pupillary responses are normal. The rest of the cranial nerves, including Weber and Rinne’s tests, are normal. Tone, power, reflexes, sensation, and coordination are normal in both the upper and lower limbs.
The Dix-Hallpike manoeuvre elicits a latent period to onset of nystagmus of 15 seconds, associated with vertigo and nausea. There is reversal of nystagmus on returning to an upright position. Fatiguing of symptoms and signs is observed on repeating the test. A contrast-enhanced CT scan of the brain is normal.
What is the likely cause of this patient’s vertigo?