The influence of handedness on the clinical presentation and neuropsychology of Alzheimer disease.

BACKGROUND Research on the influence of handedness on the clinical presentation and neuropsychology of Alzheimer disease (AD) is scarce. OBJECTIVE To compare clinical presentation and neuropsychological test performance of right- and left-handed patients with AD. DESIGN We hypothesized that left-handedness would be associated with younger onset, more rapid progression, and possibly cognitive hemispheric asymmetry. After determining handedness with the Edinburgh Inventory for Handedness for 922 patients with AD, 18 left-handed patients were compared with 18 right-handed patients matched individually on Mini-Mental State Examination scores, education, and age. We compared clinical characteristics (eg, age of onset), estimated rate of initial cognitive decline, language and visuospatial test performances, and patterns of cognitive and motor asymmetries for the 2 groups. SETTING Alzheimer's Disease Research Center at Baylor College of Medicine, Houston, Tex. MAIN OUTCOME MEASURES Results of the Wechsler Adult Intelligence Scale-Revised verbal and performance IQ tests, the Western Aphasia Battery sequential commands subtest, the Boston Naming Test, the Halstead-Reitan Finger-Tapping Test, and the calculated Rate of Initial Progression. RESULTS We found that left-handed patients had younger ages of onset but unexpectedly lower estimated rates of initial cognitive decline, and their results on language tests did not differ from those of right-handed patients. Regarding asymmetry, left-handed patients were more likely than right-handers to obtain lower verbal IQ than performance IQ scores and to exhibit faster finger-tapping speeds with their nondominant hand, but group differences did not attain statistical significance. There were disproportionately few left-handed patients with AD compared with population norms. CONCLUSIONS Left-handed patients with AD do not differ from right-handed patients in the severity or pattern of neuropsychological deficits. Left-handedness or some factor associated with it may contribute to the early appearance of cognitive deficits during the development of Alzheimer disease, but may temper the subsequent rate of progression of deficits.