Cognitive impairment in three subtypes of multiple sclerosis.

Patients with relapsing, primary progressive, and secondary progressive MS were administered the Tower of London and the Stroop Color-Word Interference Test, yielding several measures of executive function and speeded information processing. MS patients' performance was compared with healthy controls and with a clinical control group consisting of patients with rheumatoid arthritis. The MS patients performed the tests more slowly, but did not differ from either group of controls on measures of executive function. Slowing in the speed of information processing was characteristic of MS patients across two basic tasks differing in terms of controlled versus automatic processing and in terms of whether or not rapid responding was an explicit feature of successful performance. Although evident in all subtypes, this slowing was more pronounced in secondary progressive patients and somewhat less pronounced in primary progressive patients. Furthermore, the slowing was unrelated to patients' disability status or level of depression.