Idiopathic Inflammatory Myopathies

The idiopathic inflammatory myopathies include polymyositis and dermato-myositis, which tend to be responsive to drug therapy, and inclusion body myositis, which is often unresponsive or only partially responsive to drugs. Corticosteroids are considered the first line treatment of these disorders, and as well as being anti-inflammatory are immunosuppressive when used at dosages above prednisolone 20 mg/day or equivalent. In those patients who are refractory to corticosteroids, or are prone to develop complications from corticosteroids, second line drugs such as methotrexate, azathioprine or intravenous immunoglobulin should be introduced. These therapies tend to be slow acting, but response often occurs in 4 to 6 weeks and allows the dosage of corticosteroid to be reduced more rapidly. In those occasional patients with inflammatory myopathies that are refractory to corticosteroids and second line agents, one should consider adding in a third line agent such as cyclosporin, chlorambucil or cyclophosphamide. Although most clinicians would use these immunosuppressive drugs singly in combination with corticosteroids, multiple drug therapy should be considered in severe refractory cases