Affiliations: University of Iowa, Iowa City, IA, USA | Elks Rehab Hospital, Boise, ID, USA | Loyola University Chicago, Chicago, IL, USA | Mayo Clinic Scottsdale, Scottsdale, AZ, USA | University of Rochester, Rochester, NY, USA
Note: [] Statistical analysis: William Adams, MA and Douglas Langbehn, MD, PhD conducted the biostatistical analyses for the study. Correspondence to: Leigh Beglinger, Elks Rehab Hospital, 600N. Robbins Rd, Boise, ID 83701, USA. Tel.: +1 208 489 4582; E-mail: lbeglinger@elksrehab.org
Note: [] Statistical analysis: William Adams, MA and Douglas Langbehn, MD, PhD conducted the biostatistical analyses for the study.
Abstract: Background: “Practice effects” (PE), or performance improvements due to prior exposure to testing, are known to confound cognitive test results, particularly when short intervals occur between two test sessions. Objective: We examined two subsamples with short or long re-test intervals from a recent clinical trial. Methods: Thirty-four non-depressed adults with mild Huntington Disease (HD) participated. Three cognitive tests were administered at screening and again at baseline, before active treatment randomization. Half the sample had a 24-hour retest interval while the other half was >6-days. Results: The two groups differed on demographic/clinical factors (age, Total Motor Score and Total Functional Capacity). After controlling for age and motor score, PE differences were found on three of the five UHDRS cognitive tests: the longer interval group showed larger PE on Symbol-Digit Modalities and Stroop color, while the rapid interval group had larger PE on Stroop interference. Controlling for screening cognitive performance yielded similar results. Conclusions: Length of interval between screening and baseline visits and level of disease severity may influence stability of UHDRS cognitive test results in clinical trials in HD.
Keywords: Huntington disease, neuropsychological assessment, cognitive disorders/dementia, practice effects
