Insights into Reponses to Caloric and head impulse stimulation in Lateral Semicircular Canal Benign Paroxysmal Positional Vertigo.

OBJECTIVE

To investigate the pathophysiology of persistent geotropic direction-changing positional nystagmus (pGeo DCPN) by analyzing the caloric responses and clinical course in patients with pGeo DCPN and other variants of lateral semicircular canal benign paroxysmal positional vertigo (LSCC BPPV).

METHODS

In this case-control prospective study, 101 patients diagnosed with pGeo DCPN (pGeo group, N=34), persistent apogeotropic (pApo) DCPN (pApo group, N=40), or transient geotropic (tGeo) DCPN (tGeo group, N=27) involving the LSCC were enrolled. The video head impulse test (vHIT) and caloric test were performed on the day of diagnosis. If one or both of the tests.

RESULTS.: were abnormal, a follow-up test was performed after the disappearance of nystagmus. Differences in the tests.

RESULTS.: and clinical course were compared and analyzed across each type of LSCC BPPV.

RESULTS

The mean disease duration was significantly longer in patients with pGeo (23.0 days) than those with pApo (8 days) and tGeo (9 days) (p<0.005). All enrolled patients showed normal vHIT gain. Patients with pGeo demonstrated the highest canal paresis (CP) value (vs. pApo: p = 0.002 and vs. tGeo: p < 0.001) and a higher frequency of abnormal CP (61.8%) compared to pApo (22.5%) and tGeo (11.1%) groups. CP was predominantly ipsilesional (85.7%) in patients with pGeo. Follow-up caloric tests showed decreased CP in 72.7% of patients with pGeo, with 36.4% showing normalized CP after the disappearance of nystagmus.

CONCLUSION

In Conclusion, the clinical course, caloric test, and vHIT results in patients with different types of LSCC BPPV in this study implied a distinct pathophysiology for each type. The deflection of the cupula by buoyancy in pGeo DCPN could plausibly lead to CP while preserving vHIT integrity.