Ataxia in children: Viva

Branch 1: Localising the lesion

The candidate should confirm that this is a cerebellar ataxia and localise it to the cerebellum rather than to a sensory or a vestibular cause. The acute onset of a wide-based, staggering gait, the slurred speech, and the dysmetria on the finger-to-nose test point to the cerebellum, and the key distinguishing feature is that the gait is present whether the eyes are open or closed, which argues against a sensory ataxia. A strong candidate performs the Romberg test and shows that the gait does not worsen with eye closure, and tests the heel-to-shin movement, the rapid alternating movement for dysdiadochokinesia, and the eye movements for nystagmus, and confirms that the power, tone, reflexes, and sensation are normal, which separates a coordination problem from weakness. ^[1]

If the examiner presses on the topography, the candidate should explain that a truncal and gait ataxia localises to the midline vermis, which governs posture and balance, while an appendicular ataxia with dysmetria and intention tremor localises to the cerebellar hemisphere on the same side. The teaching point is that the bedside examination alone localises the lesion, and that the pattern of reflex and sensation change, such as the absent reflexes and extensor plantars of Friedreich ataxia, redirects the localisation from a pure cerebellar lesion to a multisystem degeneration. ^[1]