RISK FACTORS: Family history of autoimmune disease or vasculitis
Medical Care: Treatment of PM is empirical because of the rarity of the disease and the paucity of randomized controlled trials.
" Prednisone is the first-line treatment of choice for PM.
o Typically, the dose is 1 mg/kg/d, either as a single dose or divided. This high dose is usually continued for 4-8 weeks, until the CK level returns to reference ranges. Taper prednisone on a monthly basis by 5-10 mg until the lowest dose that controls the disease is reached.
o Monitor response to therapy by improvement in muscle strength and muscle endurance and by decrease in CK levels.
o Closely monitor patients for disease activity and adverse effects of corticosteroids such as weight gain, hypertension, osteopenia, and steroid myopathy.
o Corticosteroid myopathy can occur during the course of treatment and must be distinguished from reactivation of muscle disease. CK level is usually within reference ranges in cases of steroid myopathy. No improvement is observed with raised doses of steroids, and the condition worsens if the dose is increased.
" Immunosuppressive agents are indicated if patients do not show improvement with steroids within a reasonable period (ie, 4 wk) or if adverse effects from corticosteroids develop. Patients with poor prognostic indicators, such as dysphagia or dysphonia, are likely to require immunosuppressive agents. Under these circumstances, methotrexate is the second-line agent. Patients with IBM usually respond poorly to corticosteroids and immunosuppressive agents.
o Obtain baseline liver function tests and pulmonary functions before initiating therapy.
o Azathioprine, cyclophosphamide, chlorambucil, and cyclosporine have been used with varying success as second-line agents for PM.
" Intravenous immunoglobulin (IVIG) has been used for the short-term treatment of steroid-resistant cases of PM.
" The role of newer agents, such as TNF inhibitors, remains unclear. However, the use of TNF inhibitors in refractory cases has demonstrated some success.
" Recently, an open-label study of patients with dermatomyositis treated with rituximab (anti-CD20 monoclonal antibody) provided encouraging results. This may be a new approach to therapy for refractory cases.
" Extramuscular manifestations
o Constitutional symptoms, such as fever and fatigue, usually respond to corticosteroids.
o Articular symptoms usually resolve with treatment of the myositis. Occasionally, patients may develop a rheumatoidlike arthropathy, which may require immunosuppressive treatment such as methotrexate.
o Patients with severe interstitial lung disease may benefit from high-dose steroids and immunosuppressive treatment, especially cyclophosphamide.
o Cardiac abnormalities may respond to corticosteroids. Symptomatic arrhythmias require antiarrhythmic therapy, and symptomatic heart block is treated with placement of a pacemaker.
o Dysphagia responds either slowly or poorly to immunosuppressive therapies and may be severe enough to require enteral feeding through a gastrostomy tube or parenteral nutrition.
Diet:
" Patients may benefit from a high-protein diet. Histamine 2 receptor antagonists, proton pump inhibitors, and/or prokinetic agents may be useful in patients with esophageal reflux and dysmotility.
" Monitor patients to avoid excessive weight gain due to corticosteroid use.
" Prescribe calcium with vitamin D supplementation and oral bisphosphonates for osteoporosis prophylaxis.
Activity:
" Encourage patients to start a supervised exercise program early in the course of the disease.
" During the acute stage of the disease, patients may benefit from heat therapy, passive range of motion exercises, and splints to avoid contractures.
" Once acute inflammation is under control, the rehabilitation program should include active range-of-motion exercises and isometric contractions of the muscle groups.
" With improvement in muscle strength, patients should perform isotonic exercises with light resistance.
" Encourage patients to do 15-30 minutes of aerobic exercise when the disease is inactive.
ALTERNATIVE DRUGS Other immunosuppressant drugs such as cyclophosphamide, chlorambucil, cyclosporine can be added to steroids. Immune globulin IV added to steroids being evaluated in resistant cases, also tacrolimus. Combination methotrexate and azathioprine may also be useful in refractory cases.
PATIENT MONITORING
β’ Serial serum muscle enzyme testing
β’ Any adult should be studied for malignancy
β’ Monitor for steroid-induced metabolic complications (hypokalemia, hypertension, hyperglycemia, etc.)
β’ Bone densitometry and consideration of calcium, vitamin D, and Alendronate (Fosamax) therapy
β’ If azathioprine, methotrexate or other immunosuppressant used, then appropriate laboratory monitoring
should be done periodically.
POSSIBLE COMPLICATIONS
β’ Pneumonia
β’ Infection
β’ Myocardial infarction
β’ Carcinoma (especially breast, lung)
β’ Severe dysphagia
β’ Respiratory impairment due to muscle weakness, interstitial lung disease
β’ Aspiration pneumonitis
β’ Steroid myopathy
β’ Steroid induced diabetes, hypertension, hypokalemia, osteoporosis
EXPECTED COURSE/PROGNOSIS
β’ 30% residual weakness
β’ 20% persistent active disease
β’ 75% 5-year survival
β’ Survival worse for women and African-Americans, and patients with associated cancer
β’ Most patients improve with therapy
β’ 50% have full recovery
β’ Possibly relapsing
β’ Inclusion body myositis tends to be more steroid-refractory and includes more distal weakness