What is the true incidence of horizontal semicircular canal benign paroxysmal positional vertigo?

To assess the correct incidence of horizontal semicircular canal (H-SCC) benign paroxysmal positional vertigo (BPPV).

Retrospective assessment of patients with BPPV.

All patients with BPPV were included and the rates of involvement of posterior, horizontal, and anterior SCCs were determined.

One hundred sixty-nine patients with the diagnosis of BPPV were evaluated. One hundred forty-four patients (85.2%) were found to have posterior SCC (P-SCC) involvement, and there were 20 patients (11.8%) with horizontal SCC (H-SCC) and 2 patients (1.2%) with anterior SCC (A-SCC) involvement. Three patients (1.8%) had simultaneous H-SCC and P-SCC BPPV ipsilaterally. Geotropic nystagmus was seen in 17 out of 23 patients (73.9%) in roll test, and ageotropic nystagmus was seen in the remaining 6 patients (26.1%).

H-SCC constitutes 13.6% of all BPPV cases. H-SCC BPPV with geotropic nystagmus is more common. H-SCC BPPV can coexist with ipsilateral P-SCC BPPV. However, in some cases of H-SCC BPPV, Dix-Hallpike maneuver can cause vertigo and horizontal nystagmus. This may be confused with P-SCC BPPV. Therefore, the roll test must be performed in all cases in addition to Dix-Hallpike maneuver and both ears must be evaluated with respect to all SCCs for BPPV.

C-4.