A medical definition of fatigue in multiple sclerosis.

BACKGROUND: The symptom of fatigue has been described in a variety of ways but absence of a single taxonomy may be hindering research into this prevalent symptom.
OBJECTIVE: To define the symptom of fatigue, as experienced by patients with multiple sclerosis (MS), in terms of a common framework, typical of a medical history.
DESIGN: Qualitative phase followed by cross-sectional questionnaire survey.
METHOD: Forty patients, with clinically definite MS, underwent semi-structured interviews which were analysed within a common framework of: experience (with derived themes of motor, cognitive, somatic/energy, sleep, other features) cadence (i.e. short-term variability), chronicity, precipitating and aggravating factors, relieving factors, severity and associated features. The prevalence of each feature of fatigue, emergent from the interviews, was subsequently determined by questionnaire survey of a further 635 MS patients.
RESULTS: Despite variance across patients, fatigue could be described within the derived themes and framework. Nearly all themes were endorsed by the majority of questionnaire respondents. In summary, fatigue could be defined as reversible motor and cognitive impairment, with reduced motivation and desire to rest. It could appear spontaneously or may be brought on by mental or physical activity, humidity, acute infection and food ingestion. It was relieved by daytime sleep or rest without sleep. It could occur at any time but was usually worse in the afternoon.
CONCLUSION: A framework, not only derived from patient experience but also meaningful in a medical context, was shown to be capable of describing fatigue in a large cross-section of MS patients. The definition may facilitate inter-disease comparison of fatigue as well as physiological enquiry.