Idiopathic inflammatory myopathies

Idiopathic inflammatory myopathies are a heterogeneous group of connective tissue disorders characterized by progressive muscle weakness. Other organs - including the lungs, skin, joints, and heart - are often also involved.

Presentation is subacute or chronic and rarely acute.

May be associated with dysphagia, fatigue, difficulties with breathing, and skin lesions.

Diagnosis is confirmed by elevated serum muscle-derived enzymes, typical electromyography findings, and inflammation on muscle biopsy. Autoantibody testing is increasingly important in diagnosis and in defining the disease subtype.

For induction of remission, corticosteroids are usually first-line therapy. Immunosuppressants and intravenous immune globulin should be considered for patients who are refractory to, or intolerant of, corticosteroids.

Maintenance of remission is achieved with immunosuppressants. As corticosteroid-sparing agents, they allow the dose reduction or withdrawal of corticosteroid treatment.

Specialist multidisciplinary team involvement is essential for optimal patient outcomes.

Idiopathic inflammatory myopathies (IIMs) constitute a heterogeneous group of subacute, chronic, and, rarely, acute diseases of skeletal muscle that have in common the presence of moderate to severe proximal muscle weakness and inflammation on muscle biopsy.[1]Karpati G, Hilton-Jones D, Griggs RC. Disorders of voluntary muscle. 7th ed. Cambridge, UK: Cambridge University Press; 2001.

Based on distinct features, they are broadly divided into 3 groups: polymyositis, dermatomyositis, and inclusion body myositis.

Polymyositis and dermatomyositis seem to have an autoimmune pathogenesis, whereas inclusion body myositis seems to have an autoimmune and degenerative pathogenesis.[1]Karpati G, Hilton-Jones D, Griggs RC. Disorders of voluntary muscle. 7th ed. Cambridge, UK: Cambridge University Press; 2001.[2]Carpenter S, Karpati G. Pathology of skeletal muscle. 2nd ed. New York, NY: Oxford University Press USA; 2001.