[Benign paroxysmal positional vertigo of the horizontal canal. Clinical features in 25 patients].
To review the clinical features of benign paroxysmal positional vertigo of the horizontal canal (HC-BPPV). Retrospective study (September 1999 to March 2001) of 25 patients with HC-BPPV. Patients complained of positional vertigo associated with direction changing horizontal positional nystagmus, either geotropic or ageotropic. The horizontal nystagmus was triggered in all patients when rolled to either side in a supine position (head raised 30 degrees) and in 14 patients by the Dix Hallpike manoeuvre. The nystagmus was geotropic in 15 patients and ageotropic in 10. It varies in time in 4 patients with one change in 3 (from geotropic to ageotropic in 2 and ageotropic to geotropic in 1) and 4 changes in 10 days in another patient. In one patient with head trauma, the HC-BPPV was currently associated with ipsilateral posterior canal benign paroxysmal positional vertigo (PC-BPPV), and its characteristic rotatory-up beat nystagmus. Interestingly, 4 patients had a previous history of ipsilateral PC-BPPV and in 5 others an ipsilateral PC-BPPV occurred after the HC-BPPV. Although spontaneous recovery of HC-BPPV was common in most patients, a 270 degrees "barbecue rotation" or a "prolonged position on the healthy side" was effective in some patients. Patients with positional vertigo should undergo Dix Hallpike positioning and supine lateral head turns as this latter manoeuvre is more efficient to diagnose an HC-BPPV. Both the transformation of the positional horizontal nystagmus (geotropic-ageotropic) and the association with a PC-BPPV support the diagnosis of an HC-BPPV.