Clinical presentation of the idiopathic inflammatory myopathies

The hallmark of the inflammatory myopathies is muscle weakness. Although this feature can lead to significant disability and impairment of activities of daily living, its initial presentation may not be recognized early. Older individuals, in particular, may feel that the changes caused by myositis reflect the effects of aging rather than those of a disease process, and diagnosis, therefore, may be delayed. This factor has negative impact on the response to therapy. Inclusion body myositis, with its insidious onset in older people, and laboratory findings which may not be markedly abnormal, presents a diagnostic challenge. DM, with its characteristic symptomatic rash, is generally brought to medical attention more quickly. Another area of diagnostic concern occurs when associated organ involvement precedes myopathy. This has been observed, for example, with interstitial lung disease, and again represents a challenge to physicians. In this connection, the antisynthetase syndrome presenting with fevers, Raynaud's features, arthritis, or pulmonary involvement may not initially be recognized as a manifestation of inflammatory muscle disease. Each subgroup of IIM may present with a variety of extramuscular features that can complicate diagnosis and alter therapy and prognosis. This is particularly true for the pulmonary, GI, and cardiac manifestations and when cancer is associated with myositis. For these reasons, such features of IIM should be carefully evaluated, treated, and monitored over the course of the illness; in some cases these may play a greater role in determining the outcome of patients with IIM than the muscle involvement itself. It is hoped that in the future increased familiarity with the manifestations of the inflammatory myopathies, together with a better understanding of the underlying pathogenesis, will lead to more rapid diagnosis and more effective treatments.