Primary and Nonprimary Fatigue in Multiple Sclerosis

Using the fatigue algorithm described in the Clinical Practice Guidelines for Fatigue and Multiple Sclerosis (MS), this study aimed to determine the frequency of fatigue related directly to the MS disease process (primary fatigue) versus that related to disease symptoms such as depression (nonprimary fatigue), differentiate primary from nonprimary MS fatigue, and identify any characteristics unique to primary MS fatigue. Consecutive clinically definite MS patients from the University of British Columbia MS clinic were invited to participate. The screening assessment included standardized scales and questionnaires. In total, 50 patients completed the study. Nonprimary fatigue was present in 36 individuals (72%), of whom all but 2 had multiple factors contributing to fatigue. The most common factors contributing to nonprimary fatigue were sleep problems (58%), mobility limitations (52%), and depression (40%). Compared with patients with nonprimary fatigue, those with isolated primary fatigue had lower fatigue scores and reported fatigue onset at midday (P < .05). Any attempt to study or manage MS fatigue should be preceded by identification and amelioration of treatable nonprimary fatigue factors before focusing on primary fatigue in MS.