Which inner ear disorders lie behind a selective posterior semicircular canal hypofunction on video head impulse test?

Objective: To assess all different patterns of associated abnormalities on audiometry, bithermal caloric test (BCT) and cervical/ocular vestibular-evoked myogenic potentials (VEMPs) to air/bone-conduction in patients with selective posterior semicircular canal (PSC) hypofunction and to correlate them with underlying disorders. Study Design: Retrospective review. Setting: Tertiary referral center. Patients: 51 patients (23 men, 28 women, mean age 57.5 yr) with isolated PSC deficit (one bilateral). Interventions: Correlation with instrumental data and underlying diagnoses. Main Outcome Measures: Video-oculographic findings, objective measurements on audiometry, BCT, VEMPs and video-head impulse test (vHIT). Results: Ongoing or previous acute vestibular loss (AVL) was diagnosed in 13 patients (25.5%, 3 inferior vestibular neuritis, 10 AVL with sudden sensorineural hearing loss [SSNHL]), Meniere's disease (MD) in 12 (23.5%), cerebellopontine angle (CPA) lesion in 9 (17.6%), various causes in 7 (13.7%), benign paroxysmal positional vertigo (BPPV) involving the non-ampullary arm of PSC in 5 cases (9.8%) whereas unknown pathology in 5 (9.8%). Involvement of at least one additional receptor besides PSC was seen in 89.8% of cases. Cochlear involvement was diagnosed in 74.5% with pure-tone average significantly greater in patients with AVLþSSNHL (p<0.05). Overall involvement of labyrinthine receptors or afferents was highest in patients with AVLþSSNHL (p<0.01), MD and CPA lesions (p<0.05). Conclusions: Isolated loss of PSC function on vHIT is mostly accompanied by additional labyrinthine deficits that could only be identified through an accurate instrumental evaluation. Assessment of all receptors and afferents should be always pursued to identify the lesion site and better understand the underlying pathophysiological mechanisms.