FATIGUE AND WEAKNESS IN PATIENTS WITH INFLAMMATORY MYOPATHIES: DERMATOMYOSITIS, POLYMYOSITIS AND INCLUSION BODY MYOSITIS

Idiopathic inflammatory myopathies, including dermatomyositis (DM), polymyositis (PM) and inclusion body myositis (IBM), are chronic, debilitating diseases which are primarily characterised by weakness, fatigue and myalgia (Dalakas, 1991). The underlying reasons for these disabilities are not clearly understood. Symptoms can be partially alleviated by treatment with prednisone and immunosuppressive medications like methotrexate and/or azathioprine. However, most adult patients retain some disability and do not return to their original state of strength and endurance (HarrisLove, 2003). Thus, inflammatory myopathies have long-term effects on patients’ lifestyles and employment possibilities. Since muscle strength and fatigue are the clinical features most readily followed during treatment, extensive investigations have provided applicable clinical tests and basic physiological insights into these aspects of inflammatory myopathies. Weakness or strength is evaluated with the ability to lift weights, and fatigue or endurance is measured by patient self-assessments such as the health assessment questionnaire (HAQ), or by testing the effects of prolonged exercise (Dastmalchi et al., 2007).