Evaluation for proximal muscle weakness and rash

What is the differential diagnosis for a formerly active and healthy 70-year-old woman with worsening proximal weakness, torticollis, and a widespread raised red rash across her cheeks bilaterally? What tests do you recommend?
—LINDA SCHWAB, CNP, St. Cloud, Minn.

Dermatomyositis should be considered in the differential diagnosis of a patient with a facial rash and proximal muscle weakness. In addition to heliotrope rash (which presents as a violaceous-to-dusky erythematous rash with or without edema in a symmetrical distribution involving periorbital skin) and Gottron papules (which appear as skin papules located over bony prominences, such as the metacarpophalangeal joints, proximal interphalangeal joints, and/or distal interphalangeal joints), other cutaneous manifestations of dermatomyositis include malar erythema, poikiloderma (hyperpigmentation, hypopigmentation, and telangiectasia) in a photosensitive distribution, violaceous erythema on the extensor surfaces, periungual telangiectasias, and/or hypertrophy of the cuticle with small hemorrhagic infarcts in the hypertrophic area. In addition to routine blood tests (i.e., complete blood cell count, platelet count, and serum chemistries) and urinalysis, serologic lab evaluation specific for dermatomyositis could include muscle enzymes (creatine kinase, aldolase, aspartate aminotransferase, and lactic dehydrogenase) and myositis-specific antibodies (antinuclear, anti-Mi-2, anti-Jo-1 [antihistidyl transfer RNA synthetase], and antisignal recognition protein). Imaging studies might include MRI of the affected muscles, chest roentgenogram, barium swallow, and possibly CT scans to evaluate for a potential dermatosis-associated internal malignancy. Other tests could also include electromyography of the affected muscles, pulmonary function tests, ECG, esophageal manometry, and biopsy of the skin or muscle or both.
—Philip R. Cohen, MD
(129-10)
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