Describe a case of cerebellar ataxia which inspired an exam maneuver to detect nodulus symptoms

Case Description: A 27 year-old woman reported turning-induced dizziness after Chiari decompression. Actively turning 180° rightward triggered vertigo and left-beating nystagmus lasting >30 seconds. Turning left produced comparable vertigo and right-beating nystagmus. Passive 180° rotations in a swivel chair at ~50°/s elicited similar responses. Head-impulse-testing was normal and nonprovocative. Examination demonstrated saccadic pursuits and gaze-evoked & rebound nystagmus. Review of presurgical MRI revealed compression of both cerebellar tonsils and uvula/nodulus.

This is an ongoing prospective study. Thus far ten patients with dizziness and cerebellar ataxia and two with dizziness but no cerebellar ataxia were tested. Subjects were seated on a swivel chair with room light, rotated en bloc 180°/s for 1 second, stopped, and the presence and duration of nystagmus was recorded.

9 patients with cerebellar ataxia exhibited prolonged (5-10 seconds) nystagmus after the 180° turn. Patients without cerebellar ataxia exhibited no nystagmus after the turn. Notably, the one cerebellar ataxia patient without nystagmus had severe vestibular loss.

Inspired by observations from a patient with cerebellar ataxia and pre-operative nodulus compression, the swivel-chair test may help identify patients with clinically significant nodulus impairment. Patients with cerebellar ataxia should be asked about turn-induced dizziness, and the presence/absence of this sign may help localization and/or guide therapeutics (e.g., trial of GABA-ergic medication).