Introduction Benign positional vertigo (BPV) has a characteristic pattern of nystagmus specific to the affected semicircular canal and the underlying mechanism of canalithiasis (where otoconia float freely) or cupulolithiasis (where otoconia are adherent to the cupula).

Methods We analysed the nystagmus slow-phase velocity (SPV) profiles of 100 subjects with posterior-canalithiasis, 30 with lateral-canalithiasis, 10 with lateral-cupulolithiasis and 3 with anterior-canalithiasis. Subjects were examined on the Epley Omniax Rotator, a mechanical chair with real-time video-oculography. Video data was analysed using custom-made LabVIEW software. Nystagmus onset, duration, peak-velocity, peak-latency and time taken for the peak-velocity to halve (t50), were measured.

Results In posterior-canalithiasis, nystagmus occurred within 14.2 seconds of positioning and lasted 2.5–34.5 seconds. The median vertical peak-SPV was 37.3°/s. The median peak-latency was 2.9 seconds and the median t50 was 3.4 seconds. In lateral-canalithiasis, nystagmus onset was mostly immediate. With the affected ear down, the median peak-SPV was 52.2°/s and the median peak-latency was 3.6 seconds; the t50 was 7 seconds (median) and the paroxysms lasted 9.9–48.5 seconds. In lateral-cupulolithiasis, nystagmus onset was instantaneous. With the unaffected ear down, the median peak-SPV was 69.6°/s. The peak-latency (median 18.6 s) and t50 (median 34.5 s) were significantly prolonged compared to canalithiasis. For anterior-canalithiasis, the onset was 0–2.9 seconds, the peak-latency was 3–5.4 seconds, the t50 was 6.4–10.5 seconds and the duration was 13.4–23.1 seconds.

Conclusions Canalithiasis and cupulolithiasis produce distinct SPV profiles, which enable their identification and the separation of BPV from other causes of positional nystagmus.