Heterogeneity in executive impairment in patients with very mild Alzheimer's disease

BACKGROUND/AIMS: The presence of executive impairment in mild Alzheimer's disease (AD) has primarily been demonstrated by means of group comparison. Whether executive dysfunction is a common feature of mild AD or only present in a subgroup of patients remains unclear. The aim of this study was to describe the frequency of impairment on a set of internationally well-known executive tests in patients with very mild AD. METHODS: Thirty-six patients with very mild AD (MMSE scores above 23) and 32 healthy control subjects were administered a battery of 7 executive tests: Trail Making part B, Stroop Interference Test, modified Wisconsin Card Sorting Test (WCST), category- and letter-based verbal fluency, a design fluency task and the Similarities subtest from WAIS. Impairment was defined as a score of 2 SD or more below control means. RESULTS: Executive impairment on at least 1 measure was seen in 76% of the patients, and 50% were impaired on 2 or more tests. Trail Making B and Stroop Interference Test were impaired in more than 40%, whereas only few patients were impaired on Similarities, WCST and design fluency. A wide variation of executive test profiles was seen among the patients. CONCLUSION: Executive impairments are common in early AD and not just a feature characteristic of a subgroup of patients. Complex attentional skills are more frequently affected than other executive functions. There is, however, considerable heterogeneity among AD patients in the pattern of executive dysfunction.