Head‐shaking Nystagmus Predicts Greater Dizziness Handicap

Methods: Fifty-three adult patients with unilateral peripheral hypofunction and ten healthy controls. Unilateral vestibular hypofunction was defined by the caloric test of the videonystagmography (VNG). Patients and controls underwent BedHSN testing. Patients completed the New Version Dizziness Handicap Inventory (DHI) (Appendix 1) and the Functional Level (FL) (Appendix 2) questionnaires . The sensitivity and specificity of BedHSN in diagnosing unilateral vestibular hypofunction defined by VNG caloric testing, and by abnormal gain and symmetry of the VOR by rotary chair testing was calculated. Score of self-perceived handicap were compared between subjects with and without a BedHSN by Wilcoxon rank test (significance level = 0.05). Bedside HSN and VNG: The bedside head-shaking test was performed by having the patient wear Frenzel lenses in darkness. The clinician rotated the patient’s head in the plane of the horizontal semicircular canal 30 times at 1-2 Hz. A positive BedHSN is the presence of at least 5 beats of nystagmus. Only patients with horizontal biphasic nystagmus were included in this study. The VNG(iVNG, Balanceback, Boca Raton, FL, USA) test battery included oculomotor testing, high frequency headshake, positioning and positional testing, and bithermal water calorics at temperatures of 44°C and 30°C. The maximum slow phase velocity of nystagmus was calculated for each irrigation. Using Jonkees’ formula, a unilateral weakness of > 25% was considered abnormal. The patient's head was rotated in the horizontal plane for 20 s and eye movements were recorded for 20 s post stimulus. Rotational chair testing (I-Portal NOTC, Neuro Kinetics Inc., Pittsburgh, PA, USA) was also employed to assess VOR. Sinusoidal harmonic acceleration testing was performed at six frequencies ranging from 0.01 -0.32 Hz. Abnormal findings were considered if values fell outside of normal at two or more frequencies for gain, phase and symmetry.