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

OBJECTIVE: To assess the correct incidence of horizontal semicircular canal (H-SCC) benign paroxysmal positional vertigo (BPPV). STUDY DESIGN: Retrospective assessment of patients with BPPV. METHODS: All patients with BPPV were included and the rates of involvement of posterior, horizontal, and anterior SCCs were determined. RESULTS: 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 %). CONCLUSION: 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.