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Last Updated: 2/18/2015  

Idiopathic Inflammatory Myopathies

  • Ask about truncal and proximal-muscle weakness.

  • Ask about medications (e.g., corticosteroids, statins) and excessive alcohol use that could otherwise explain 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.

  • Consider sporadic inclusion body myositis in persons over age 50 with slow onset and slowly progressive asymmetric weakness in both proximal and distal muscles (quadriceps and finger flexors are classically affected).

  • 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.

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

  • 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 of 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 in addition to solar avoidance 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.
Author(s) and Disclosures:
Nancy J. Olsen, MD has nothing to disclose. David Freeman, MD has nothing to disclose. Joshua L. Fenderson, MD has nothing to disclose. Jefferson Roberts, MD, LTC has nothing to disclose.

One or more of the present or past ACP Smart Medicine physician editors worked on this module and had nothing to disclose: Davoren Chick, MD, FACP; Deborah Korenstein, MD, FACP; Marjorie Lazoff, MD, FACP; Richard Lynn, MD, FACP.

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