[Postural sway in patients with hereditary ataxia].

Instability of erect stance in patients with autosomal dominant hereditary ataxia was investigated by posturography. Postural sway on a force-measuring platform was measured quantitatively and sway frequencies were analyzed. Thirty patients from 27 families (15 men and 15 women, mean age of 53.1 years (SD 11.1)) were divided into two clinical groups. Twelve patients (group A) had "pure" cerebellar signs with no somatosensory afferent symptoms. Eighteen patients (group B) had sensory disturbances or diminished reflexes of the lower limbs, and a delayed latency of scalp P37 in somatosensory evoked potentials subsequent to tibial nerve stimulation. Postural sway of the patients of both groups was larger than that of normal subjects. Group A patients had a high antero-posterior/lateral sway ratio. Group B patients had increased sway with eyes closed. With respect to sway frequencies, group A patients had a power spectrum peak around 3 Hz. Group B patients had a power spectrum peak around 1 Hz, and twelve of them had another 3 Hz component. Atrophy of the anterior lobe of the cerebellum shown by MRI was more prominent in patients who had the 3 Hz power spectrum peak than in patients lacking the 3 Hz peak. Quantitative posturography was useful to detect disturbances of the anterior lobe of the cerebellum and the spinal ascending system in patients with autosomal dominant hereditary ataxia.