Reversible post–head-shaking nystagmus in horizontal canal BPPV as a mechanical mimic of vestibular hypofunction: a case report

PURPOSE: To describe transient post-head-shaking nystagmus associated with horizontal canal benign paroxysmal positional vertigo (BPPV) and its resolution following canalith repositioning. METHODS: A 78-year-old woman presented with positional vertigo. Video-oculography revealed left-beating pseudo-spontaneous nystagmus and a robust left-beating pHSN, initially suggestive of uncompensated unilateral vestibulopathy. Further bedside assessment, including the Head Pitch test and Supine Roll test, demonstrated direction-changing horizontal nystagmus consistent with left horizontal canalolithiasis. RESULTS: After an unsuccessful Lempert maneuver, a Gufoni maneuver was performed, resulting in immediate resolution of vertigo and nystagmus. At 10-day follow-up, no spontaneous, positional, or post-head-shaking nystagmus was observed. The patient remained asymptomatic throughout 14-month follow-up, with preserved horizontal vHIT responses at reassessment. CONCLUSION: This case suggests that post-head-shaking nystagmus in horizontal canal BPPV may arise from transient mechanically triggered asymmetry rather than a fixed vestibular deficit. Reliance on pHSN alone may lead to misdiagnosis and inappropriate diagnostic interpretation. Incorporating positional testing and reassessment following canalith repositioning may help avoid misinterpretation of post-head-shaking nystagmus as unilateral vestibular hypofunction.