Benign paroxysmal positional vertigo and head position during sleep.

To determine whether any particular head positions during sleep are associated with BPPV, head position during sleep was monitored for 3 days in 50 BPPV patients after the disappearance of positional nystagmus and in 25 normal control subjects. A gravity sensor was attached to the center of the subject's forehead at home. The positional angle of the head was measured at 5-second intervals during sleep. In BPPV, the posterior semicircular canal was involved in 40 patients and the lateral semicircular canal in 10 patients. Recurrence was found in 22 of 50 BPPV patients. BPPV patients with recurrence were significantly more likely to sleep in the affected-ear-down 45-degree head position than were patients with no history of recurrence (P< 0.02). When the head is in the affected-ear-down 45-degree head position, the non-ampullated half of the posterior semicircular canal and the non-ampullated half of the lateral semicircular canal are nearly in the earth-vertical position, making it easier for detached otoconia to fall into the posterior or lateral semicircular canal and to agglomerate and attain a certain size in the lowest portion of each semicircular canal. Our findings showed that the affected-ear-down 45-degree head position during sleep could be an etiological factor of BPPV, more particularly in patients with recurrent BPPV.