Polymyositis and Dermatomyositis (Continued)

Because malignancy may be associated with PM (up to 10% of patients), and especially with DM (up to 25% of patients older than 40 years), screening for cancer (carcinomas of the breast and ovary in women and lower gastrointestinal tract in men) is important, especially in older adults; routine laboratory studies, testing stool for occult blood, and selected imaging studies, including mammography and computed tomography (CT) scanning of the chest and abdomen, are performed.

The severity of disease, as well as response to treatment and prognosis of DM and PM, are quite variable and range from those with mild weakness, who quickly respond to treatment, to progressively worsening weakness that may be resistant to a number of therapies. Poor prognostic factors are associated with a more than 6-month delay in initiation of therapy from the onset of weakness, dysphagia, interstitial lung disease (Jo-1–positive patients), underlying malignancy, presence of collagen-vascular disorders, and cardiac involvement. Other clinical features, such as advanced age, severity of weakness, peak of CK elevation, and degree of abnormality on muscle biopsy, do not reliably predict the disease course or treatment response.

Corticosteroids treatment is the initial therapy for both DM and PM. Typically, prednisone is started at 1 mg/kg per day, with a maximum daily dose of 80 mg. For patients with severe weakness, intravenous glucocorticoid therapy is indicated (methylprednisone 1000 mg/day for 3 days), followed by high-dose oral prednisone. Weakness usually improves over days to a few weeks. Once muscle strength is significantly improved and stabilized, a slow, gradual taper of prednisone (5-10 mg every 2-3 weeks) is started, aiming for the lowest and yet still effective dose to achieve sustained improvement. This may take up to a year. Patients on long-term corticosteroid treatment are treated with calcium, vitamin D, and bisphosphonates (for osteoporosis prevention); antacid or H2 blocker (for gastric mucosa protection); and prophylaxis (usually with Bactrim) for opportunistic infections. In up to 30% of patients, weakness recurs as the dose of prednisone is tapered, and a corticosteroid-sparing immunosuppressive agent is required. Azathioprine, methotrexate, cyclosporine, and mycophenolate mofetil are useful agents in this setting.

Physical therapy and exercise are recommended early in the course of treatment and are tailored to the degree of weakness. Stretching and range of motion exercises are helpful in preventing joint contractures (especially in weak muscles). Appropriate exercise programs, from low levels of isometric and resistive exercises in those with moderate weakness to increasing levels of activity in those with mild weakness, are encouraged throughout the course of disease. Patients with DM may have increased photosensitivity and are asked to avoid prolonged exposure to ultraviolet light.

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