Fatigue is one of the most common and debilitating symptoms affecting persons with multiple sclerosis, reported by at least 75% of persons with multiple sclerosis at some point in the disease course (Krupp 2006; Lerdal et al 2007). Due to its subjectivity, the clinical manifestations of fatigue in the context of multiple sclerosis vary widely between subjects and may be interpreted differently depending on cultural or educational backgrounds. Commonly defined as a “lack of energy,” other descriptors that may be used for fatigue in multiple sclerosis include “tiredness, asthenia, lassitude, malaise, lack of motivation, weakness, weariness, or difficulty initiating/sustaining voluntary effort” (Mills and Young 2008). Other subjects may use the term “sleepiness” as a descriptor (Attarian et al 2004; Mills and Young 2008).
Frequency also varies widely. Symptoms of fatigue may be constant or intermittent or may fluctuate with clinical disease worsening, such as a multiple sclerosis relapse. Hot environments may trigger or worsen fatigue in heat-sensitive subjects (Lerdal et al 2007). Severity can also vary between subjects or within the same subject throughout the course of the disease.