Idiopathic inflammatory myopathies

Heterogeneous group of muscular disorders characterized by progressive muscle weakness.

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 EMG findings, and inflammation on muscle biopsy.

Corticosteroids are first-line therapy. Intravenous immunoglobulin, methotrexate, and azathioprine are used as second-line therapy. Third-line therapies include cyclophosphamide, mycophenolate, cyclosporine, and tacrolimus.

Idiopathic inflammatory myopathies 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 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.