Podokinetic after-rotation in patients with compensated unilateral vestibular ablation

Previous studies showed that after stepping-in-place on a rotating turntable, blindfolded subjects cannot step-in-place on firm ground. Instead they involuntarily turn themselves relative to space in the same direction as they were turning relative to the rotating turntable. This phenomenon has been termed podokinetic after-rotation (PKAR). PKAR comprises a brief exponentially rising phase of response during the first 2 min followed by a prolonged second phase of slow exponential decline during the next 28 min. Here we ask whether PKAR is modified in patients with compensated unilateral vestibular loss. Eleven patients who had previous vestibular ablation underwent (1) a Fukuda-like control stepping test, (2) podokinetic adaptation to 30 min of stepping in place on the centre of a turntable rotating at 45 deg/s and (3) PKAR. Control tests showed that the blindfolded patients had no significant rotational bias while stepping-in-place on the ground for 1 min. After 30 min of adaptation, the 2-min rising phase of PKAR was indistinguishable from normal. In contrast, the subsequent 28-min phase of exponential decline showed a lesion-dependent asymmetry. PKAR had significantly higher mean velocities toward the side of the lesion than away from the lesion. The observed PKAR asymmetry may signify occult residual static vestibular imbalance.