Clinical case · clinician

Progressive ataxia with prolonged MCT latencies

Vignette

A 71-year-old man presents with 18 months of progressive imbalance, mild dysarthria, and saccadic dysmetria. He has a family history of late-onset cerebellar ataxia. Examination shows gaze-evoked nystagmus, broken pursuit, and a wide-based gait. Head impulse test is normal in all six semicircular canal planes. Caloric responses are symmetric and within normal limits. MRI shows mild cerebellar atrophy.

CDP findings

SOT pattern vs normal
Centralage norm 700255075100EQS73C1EO ·F66C2EC ·F67C3EO ·F·Sw50C4EO ·Sw28C5EC ·Sw30C6EO ·Sw·Sw
MCT — medium-amplitude backward translation
platform184 ms-100-500+50+100COP mm0200400600800100012001400Central · backward · medium
ADT — sway energy across five trials per direction
sway energy025507510090T183T270T395T475T5Toes upadapting86T186T284T385T483T5Toes downno adaptation

Single-best-answer

Which CDP triad most supports a central rather than a peripheral diagnosis?

Teaching point. Central involvement is suggested by the triad of diffuse SOT abnormality, prolonged MCT latency reflecting long-loop pathway involvement, and failure of central adaptation on ADT. Normal HIT with abnormal CDP is itself a useful 'central pattern' clue.

References