A 10-year-old girl complains of persistent redness of the skin over her knuckles and around the nail beds. She describes easy fatigability and can rise only with difficulty from a squatting position. Physical examination reveals erythema over the knuckles and a heliotropic rash. A muscle biopsy shows infiltrates of B and T lymphocytes around blood vessels and in connective tissue of the perimysium. Elevated serum levels of which of the following would be expected in this patient?

Creatine kinase. The inflammatory myopathies represent a heterogeneous group of acquired disorders, all of which feature symmetric proximal muscle weakness, increased serum levels of muscle-derived enzymes, and non-suppurative inflammation of skeletal muscle. They are thought to have an autoimmune origin. The most common morphologic characteristics in the inflammatory myopathies are (1) inflammatory cells, (2) necrosis and phagocytosis of muscle fibers, (3) a mixture of regenerating and atrophic fibers, and (4) fibrosis. Dermatomyositis is distinguished from the other myopathies (i.e., polymyositis and inclusion body myositis) by the presence of a characteristic heliotropic rash on the upper eyelids, face, and trunk. Patients with inflammatory myopathies have increased serum levels of creatine kinase and other muscle enzymes. Elevated serum alkaline phosphatase (choice A) is associated with liver and bone disease. Alpha-fetoprotein and carcinoembryonic antigen (choices B and C) are markers of neoplasia. Elevated blood urea-nitrogen (choice E) is associated with renal disease.Diagnosis: Dermatomyositis