Specificity of frontal dysfunctions in relapsing-remitting multiple sclerosis.

Various studies have reported deficits in frontal cognitive functions in patients with multiple sclerosis (MS). However, the frontal deficit is not uniform and is often very subtle. The aim of this study was to assess frontal functions in a broad sample of patients with relapsing-remitting multiple sclerosis at the mild-to-moderate stage. The sample included a series of 165 patients. We used a test battery covering the frontal functions that have been described as being altered in MS. Significant differences were found between the patient group and healthy controls on the WAIS Arithmetic subtest, the PASAT, category word recall and the number of trials required to reach the first category of the WCST. In conclusion, we observed significant differences with respect to the control group in terms of information processing speed and working memory. These functions involve connections between the frontal lobe and other brain regions.

Regression to the mean in multiple sclerosis.

In order to ensure sufficient disease activity, patients with relapsing remitting (RR) multiple sclerosis (MS) are often included in randomized placebo-controlled trials, only if they have a high baseline activity. These patients, whose evolution is unusual in the pre-study period, will tend to show a more usual behavior when followed up over a period of time. This phenomenon is known as regression to the mean. Regression to the mean should be taken into account in correctly interpreting long-term studies of cohorts treated without a placebo control group, which use the baseline period as control. The aim of this study was to evaluate the relevance of this phenomenon in a non-treated cohort of RRMS patients, selected with similar criteria to those used in randomized placebo-controlled clinical trials. Forty-four patients with definite RRMS, with two or more relapses in the previous two years, and a baseline EDSS < or = 5.5 were prospectively followed. The mean number of relapses spontaneously decreased from 1.72 (SD: 1.4) in the year prior to enrolment, to 1.0 (SD: 1.3) during the first year of follow-up (P < 0.05). Regression to the mean may explain as much as 40% of the reduction in the relapse rate from the baseline period to the period on-study.