Abstract: Fatigue is one of the most common symptoms of multiple sclerosis (MS), and it can have a major impact on health-related quality of life. Therefore, it is imperative that healthcare practitioners regularly assess fatigue in their patients with MS. Fatigue can be caused either by the disease process (primary fatigue) or by other problems such as insomnia, infections, or depression (secondary fatigue). Because the causes of secondary fatigue are generally amenable to treatment, it is important that healthcare practitioners distinguish between the two types of fatigue when assessing and treating fatigue. Because fatigue is a subjective experience, it can be difficult to ...