To determine the prevalence of cerebellar ataxia in patients with HD, both early and late on HD progression and correlate with the degree of involvement of classic motor symptoms.

Huntington's disease (HD) is a hereditary degenerative disorder characterized by progressive motor, cognitive and psychiatric changes. Motor symptoms are expressed by chorea and other movement disorders, but the prevalence of ataxia is considered as low during the course of the disease.

We performed a multicentric cross-sectional study, in 4 specialized centers in Brazil, in which we evaluated 124 patients with genetic diagnosis of HD. Patients with advanced dementia, physical limitations or asymptomatic were excluded, so 71 patients were considered eligible. We applied scales used for assessing ataxia as SARA (Scale for Assessment and Rating of Ataxia) and BARS (Brief Ataxia Rating Scale) in all patients, in addition to the Unified Huntington's Disease Rating Scale (UHDRS).

41 patients had initial presentation of chorea, 12 of psychiatric disorder, 6 presented as ataxia, 3 with cognitive signs, 1 with parkinsonism, 1 with tics and 7 was undetermined. 67 patients had more than 3.5 points on SARA scale, representing 94% of the patients. 25% of the patients evaluated had 10 points or higher on the SARA scale, despite having 40 points or less on the UHDRS scale. The genetic expansion CAG ranged from 39 to 56 and was not correlated to the symptom of ataxia.

The prevalence of cerebellar ataxia in HD is very high and it seems to be an early event during the pathological process of HD, so that ataxia can be seen as first symptom. Chorea and other signs assessed by UHDRS don't progress proportionally to the symptoms of ataxia, suggesting that the damage to the cerebellum does not develop simultaneously with, but independently, from the well-known classical lesions in the striatum.