Retest effects and cognitive decline in longitudinal follow-up of patients with early HD.

Objective: To assess the natural progression of cognitive impairment in Huntington's disease (HD) and to reveal factors that may mask this progression.
Background: Although numerous cross-sectional studies reported cognitive deterioration at different stages of the disease, progressive cognitive deterioration has been, up to now, difficult to demonstrate in neuropsychological longitudinal studies.
Methods: The authors assessed 22 patients in early stages of HD at yearly intervals for 2 to 4 years (average, 31.2 +/- 10 months), using a comprehensive neuropsychological battery based on the Core Assessment Program for Intracerebral Transplantation in Huntington's Disease (CAPIT-HD).
Results: The authors observed a significant decline in different cognitive functions over time: these involved primarily attention and executive functions but also involved language comprehension, and visuospatial immediate memory. Episodic memory impairment that was already present at the time of enrollment did not show significant decline. The authors found a significant retest effect at the second assessment in many tasks.
Conclusion: Many attention and executive tasks adequately assess the progression of the disease at an early stage. For other functions, the overlapping of retest effects and disease progression may confuse the results. High interindividual and intraindividual variability seem to be hallmarks of the disease.