Correlates of early disability in Huntington's disease

Functional disability in Huntington's disease usually results from a combination of the movement disorder, intellectual decline, and psychopathological changes, but the unique contribution of each element has never been investigated. The Shoulson‐Fahn functional capacity rating scale measures independence in such daily activities as eating, dressing, and managing personal finances, and is used to stage the illness and follow its progression. To determine which problems contribute most to reduced functional capacity as the disease evolves, we reviewed the records of 48 consecutive patients who were evaluated for intellectual and emotional status and motor disability. Each patient was staged and rated for functional capacity at the time of the examinations. Thirty‐three of these patients were followed over several years with repeat evaluations at 6‐month intervals. Intellectual impairment and depression correlated significantly with reduced functional capacity. However, when the somatic symptoms of depression were eliminated from the analysis, its relationship to functional capacity was no longer significant. Duration of illness, motor disability, and age at onset also had little impact. Neuropsychological test performance and functional capacity deteriorated over time. Our data suggest that intellectual impairment is a major factor in reducing functional capacity in the early stages of Huntington's disease.