Diffuse, inflammatory myopathies of unknown cause, polymyositis and dermatomyositis produce symmetrical weakness of striated muscle — primarily proximal muscles of the shoulder and pelvic girdles, neck, and pharynx. In dermatomyositis, such muscle weakness is accompanied by cutaneous involvement. These diseases usually progress slowly, with frequent exacerbations and remissions. They occur in twice as many females as males (except dermatomyositis with malignant tumor, which is most common in males older than age 40).
The prognosis usually worsens with age. Death commonly occurs from associated cancer, respiratory disease, or heart failure or from the adverse effects of drug therapy. On the other hand, 80% to 90% of affected children regain normal function with proper treatment. However, if untreated, childhood dermatomyositis may progress rapidly to disabling contractures and muscle atrophy.
Although the cause of polymyositis remains puzzling, researchers believe that it may result from an autoimmune reaction. Presumably, the patient’s T cells inappropriately recognize muscle fiber antigens as foreign and attack muscle tissue, causing diffuse or focal muscle fiber degeneration. (Regeneration of new muscle cells then follows, producing remission.) Polymyositis and dermatomyositis may be associated with other disorders, such as allergic reactions; systemic lupus erythematosus (SLE); scleroderma; rheumatoid arthritis; Sjögren’s syndrome; carcinomas of the lung, breast, or other organs; systemic viral infection; or d-penicillamine administration.
Annual incidence is 1 in 100,000 people.
Polymyositis begins acutely or insidiously with muscle weakness, tenderness, and discomfort. It affects proximal muscles more than distal muscles and impairs performance of ordinary activities. The patient may have trouble getting up from a chair, combing his hair, reaching into a high cupboard, climbing stairs, or even raising his head from a pillow. Other muscular symptoms include inability to move against resistance, proximal dysphagia, dysphonia, and difficulty breathing.
In dermatomyositis, an erythematous rash usually erupts on the face, neck, upper back, chest, and arms as well as around the nail beds. A characteristic heliotropic rash appears on the eyelids, accompanied by periorbital edema. Gottron’s papules (violet, flat-topped lesions) may appear on the interphalangeal joints.
Other tests differentiate polymyositis from diseases that cause similar muscular or cutaneous symptoms, such as muscular dystrophy, advanced trichinosis, psoriasis, seborrheic dermatitis, and SLE.
Typical laboratory results in polymyositis include elevated erythrocyte sedimentation rate, elevated white blood cell count, and elevated muscle enzyme levels (creatine kinase, aldolase, and serum aspartate aminotransferase) not attributable to hemolysis of red blood cells or hepatic or other diseases. Other laboratory results include increased urine creatine level (more than 150 mg/24 hours), decreased creatinine level, and positive antinuclear antibodies. Electromyography shows polyphasic short-duration potentials, fibrillation (positive spike waves), and bizarre high-frequency repetitive changes.
High-dose corticosteroid therapy relieves inflammation and lowers muscle enzyme levels. Within 2 to 6 weeks after treatment, serum muscle enzyme levels usually return to normal, and muscle strength improves, permitting a gradual tapering down of corticosteroid dosage. If the patient responds poorly to corticosteroids, treatment may include cytotoxic or immunosuppressant drugs. Supportive therapy includes bed rest during the acute phase, range-of-motion (ROM) exercises to prevent contractures, analgesics and application of heat to relieve painful muscle spasms, and diphenhydramine to relieve itching. Patients older than age 40 need thorough assessment for coexisting cancer.
❑ Assess level of pain, muscle weakness, and ROM daily. Give analgesics as needed.
❑ If the patient is confined to bed, prevent pressure ulcers by giving good skin care. To prevent footdrop and contractures, apply high-topped sneakers, and assist with passive ROM exercises at least four times daily. Teach the patient’s family how to perform these exercises on the patient.
❑ If 24-hour urine collection for creatine or creatinine is necessary, make sure your coworkers understand the procedure. When you assist with muscle biopsy, make sure the biopsy isn’t taken from an area of recent needle insertion.
❑ If the patient has a rash, warn him not to scratch, as it may cause infection. If antipruritic medication doesn’t relieve severe itching, apply tepid sponges or compresses.
❑ Encourage the patient to feed and dress himself to the best of his ability but to ask for help when needed. Advise him to pace his activities to counteract muscle weakness. Encourage him to express his anxiety. Ease his fear of dependence by reassuring him that muscle weakness is probably temporary.
❑ Explain the disease to the patient and his family. Prepare them for diagnostic procedures and possible adverse effects of corticosteroid therapy (weight gain, hirsutism, hypertension, edema, amenorrhea, purplish striae, glycosuria, acne, and easy bruising). Advise a low-sodium diet to prevent fluid retention. Emphatically warn against abruptly discontinuing corticosteroids. Reassure the patient that steroid-induced weight gain will diminish when the drug is discontinued.
Review other book chapters online related to Dermatomyositis:
Copyright notice for book excerpts: Copyright © 2008 Lippincott Williams & Wilkins. All rights reserved.
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Title: Professional Guide to Diseases (Eighth Edition)
Authors: Springhouse
Publisher: Lippincott Williams & Wilkins
Copyright: 2005
ISBN: 1-58255-370-X
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