polymyositis and dermatomyositis

Polymyositis

Dermatomyositis

This patient has a proximal myopathy as evidenced by an elevated creatine kinase level, and difficulty rising from a chair and climbing stairs. Insidious onset of symmetric proximal myopathy associated with Gottron's papules or a heliotrope rash is highly characteristic of dermatomyositis (DM).

Antinuclear antibodies (ANA) screening is the initial test of choice as it is positive in approximately 80% of these patients. Evaluation also includes specific antibody testing including anti-Ro, anti-La, anti-Sm, anti-ribonucleoprotein (RNP), and anti-Jo-1 antibodies. Chest x-ray is performed to screen for interstitial lung disease if no pulmonary symptoms are present. In symptomatic patients, or those with abnormal x-ray findings, chest CT and pulmonary function testing are recommended.

Tissue biopsy (muscle/skin) is not required in patients with highly characteristic features of DM in the absence of alternative diagnoses. Patients with nonspecific findings (eg, facial erythema, psoriasiform scalp lesions), isolated skin/muscle involvement, or negative antibody testing may need tissue diagnosis.

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