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Last Updated: 1/24/2013  

Dermatomyositis and Polymyositis

Diagnosis
  • Ask about truncal and proximal-muscle weakness.

  • Ask about medications (e.g., corticosteroids, statins) and excessive alcohol use that might cause a myopathy.

  • Look for a pattern of bilateral proximal-muscle weakness and note absence of muscle fasciculations, oculomotor and lower facial muscle weakness, sensory symptoms, spastic reflexes, and muscle tenderness.

  • Examine the patient for the characteristic rashes of dermatomyositis, including the heliotrope of the upper eyelids and periorbital tissues; scaly purple plaques over metacarpal and interphalangeal joints; cracked horizontal lines on palmar and lateral aspects of fingers (mechanic's hands); erythematous, papular eruptions on sun exposed areas.

  • Obtain CK (or aldolase, ALT, AST) and exclude other causes of CK elevation, such as drugs, alcohol, and hypothyroidism.

  • Obtain a muscle biopsy as the most definitive test to diagnose polymyositis, a muscular dystrophy, inclusion body myositis, or some other uncommon disease; MRI can help localize the site of muscle biopsy, if needed.

  • Obtain age- and sex-appropriate cancer screening in all patients; some experts obtain endoscopic and imaging studies to exclude pharyngeal, GI, pulmonary, intra-abdominal, and pelvic and ovarian malignancies.

Hospitalization
  • Hospitalize patients with rapidly developing weakness, significant functional impairment, and signs of pulmonary or other serious complications.

Therapy
  • Refer patients for exercise therapy programs.

  • Start prednisone at a high dose, 1 mg/kg·d, and taper as tolerated to approximately 10 mg/d.

  • Add either weekly methotrexate, 7.5 to 25 mg/wk, or daily azathioprine, up to 150 mg/d, soon after starting prednisone.

  • Assess potential benefits and harms of a short course of intravenous immunoglobulin as an adjunct in severe or refractory cases.

  • Prescribe alendronate or risedronate with calcium and vitamin D for all patients receiving high doses or long-term steroids.

  • Reevaluate the patient if there is no response to therapy and consider looking for clinical and biopsy evidence of inclusion body myositis.

  • Use topical therapies and antimalarials to treat the skin manifestations of dermatomyositis.

DOI: 10.7326/d285
The information included herein should never be used as a substitute for clinical judgment and does not represent an official position of ACP.
Disclosures:
Nancy J. Olsen, MD has no financial relationships with pharmaceutical companies, biomedical device manufacturers, or health-care related organizations. David Freeman, MD Carney Hospital; Lahey Clinic
Boston, MA; Burlington, MA
has no financial relationships with pharmaceutical companies, biomedical device manufacturers, or health-care related organizations.
David Freeman, MD Carney Hospital; Lahey Clinic
Boston, MA; Burlington, MA
has no financial relationships with pharmaceutical companies, biomedical device manufacturers, or health-care related organizations.
Deborah Korenstein, MD, FACP, Editor in Chief, ACP Smart Medicine, has no relationships with any entity producing, marketing, re-selling, or distributing health care goods or services consumed by, or used on, patients. Richard B. Lynn, MD, FACP, Editor, ACP Smart Medicine, has no relationships with any entity producing, marketing, re-selling, or distributing health care goods or services consumed by, or used on, patients.
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