Longitudinal evaluation of cognitive disorder in Huntington's disease

The study investigated longitudinal change in cognitive function in 87 pati ents with Huntington's disease (HD), using a range of neuropsychological te sts, which tap mental manipulative abilities, memory, and frontal executive skills. Over a 1-year period the largest changes were noted in letter flue ncy, object recall, and Stroop Test performance, whereas no changes were no ted over more than 3 years on the modified Wisconsin Card Sorting Test. Con trary to expectation, greater change was evident over 1 year for tasks with low compared to high cognitive demands. The differential sensitivity of ta sks was attributed in part to inherent characteristics of the tests themsel ves: their capacity to detect minor gradations of change and their vulnerab ility to practice effects. However, the greater change for relatively autom atic, speed-based tasks with low cognitive demands was interpreted as refle cting the evolution of HD, with a greater magnitude of change occurring in basal ganglia than cortical function. One purpose of the study was to ident ify tasks sensitive to the progression of HD and hence most suitable for th e evaluation of therapies. Despite reaching statistical significance by vir tue of the large group size, numerical differences in test scores over 1 ye ar were very small, suggesting that the use of such tests to evaluate chang e in individuals or small groups of subjects would he problematic. The data highlight the slow progression of HD, the limitations of standard cognitiv e tests in detecting change over short periods, and the need for therapeuti c studies that encompass a relatively prolonged time frame.