The association between cognitive impairment and physical disability in multiple sclerosis.

BACKGROUND: The association between cognitive impairment and physical disability was examined in a larger, more representative sample of patients with multiple sclerosis (MS) than in previous studies.
METHOD: Two hundred and fifty-three patients attending an MS clinic were assessed with respect to physical disability using the Expanded Disability Status Scale and cognitive impairment using a battery of neuropsychological tests.
RESULTS: Physical disability correlated with duration of disease; cognitive impairment did not. Virtually all measures derived from the cognitive battery were significantly correlated with physical disability. Three measures of speeded information processing and one involving delayed recall of verbal material were unique predictors of disability status. The relationship between cognitive impairment and physical disability was equivalent for patients with shorter (< 3 years) versus longer (> 10 years) disease duration. Cognitive impairment correlated with the rate of disability progression as reflected by the progression index.
CONCLUSION: Cognitive impairment is more closely associated with physical disability than most previous studies indicate. This relationship appears to be stable throughout the duration of MS, although this conclusion is qualified by the cross-sectional design of the study. Further attention should be paid to cognitive impairment as a possible predictor of the rate of patients' physical decline.