Posterior canal benign paroxysmal positional vertigo with long duration: Heavy or light cupula?

OBJECTIVE: To investigate the characteristics of positional nystagmus in posterior semicircular canal (PSCC) benign paroxysmal positional vertigo (BPPV) patients with longer durations, and to discuss the possible underlying mechanism of this nystagmus. METHODS: We conducted a retrospective review, and enrolled 118 consecutive patients with unilateral PSCC BPPV. The duration of nystagmus during a Dix‐Hallpike test was classified into short (<1 min) and long (≥1 min) durations. For the identification of a neutral point in PSCC BPPV patients with long durations, the patient's head was turned 45° to the lesioned side to set the affected PSCC on the sagittal plane, and the disappearance of positional nystagmus was investigated in a pitch plane. RESULTS: Among 118 patients with PSCC BPPV, positional nystagmus during a Dix‐Hallpike test showed short durations (<1 min) in 112 patients and long durations (≥1 min) in 6 patients. Of 6 PSCC BPPV patients with a long duration, a neutral point was identified in 5 patients whose nystagmus lasted for longer than 2 min; interestingly, a neutral point was observed when the patient's head was slightly tilted backward in all 5 patients. CONCLUSION: Considering that a neutral position was identified when the patient's head was slightly tilted backward while keeping the head turned 45° to the right or left, we assume that the light cupula condition of the ipsilateral PSCC or the contralateral anterior semicircular canal, and not PSCC BPPV cupulolithiasis, could be responsible for the occurrence of persistent torsional‐upbeating nystagmus in a Dix‐Hallpike test. LEVEL OF EVIDENCE: 4