A 58-year-old man undergoes Dix-Hallpike testing which produces purely downbeating nystagmus immediately upon positioning, with no latency, no rotatory component, no fatigability on repetition, and reproduction of symptoms each time. The most likely diagnosis is:

• A Posterior canal BPPV of the dependent ear
• B Anterior canal BPPV
• C Meniere's disease
• D Central positional nystagmus from a posterior fossa lesion ✓

Explanation

Central positional nystagmus begins without latency, is non-fatiguing, often purely vertical (typically downbeating), and recurs identically on retesting because it arises from disinhibition of the vestibulo-ocular reflex by cerebellar or brainstem lesions. Posterior canal BPPV gives latent, fatigable upbeat-torsional nystagmus, and anterior canal BPPV gives downbeating-torsional nystagmus with a torsional component and latency, killing options A, B and C.

Reference: Scott-Brown's Otorhinolaryngology Head and Neck Surgery, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.