The correct answer is A. Creatine kinase (CK), aldolase
This patient had dermatomyositis (DM). The cutaneous manifestations of DM can be categorized into pathognomonic, characteristic, compatible, less common, and rare. In this patient, she had one pathognomonic (Gottron papules: erythematous papules with scale on the knuckles), and several characteristic (periungual erythema, capillary dropout with thrombosis) findings. In suspected DM cases, the recommended baseline laboratory tests include CK, aldolase, aspartate aminotransferase (AST) and lactate dehydrogenase (LDH).
Serum tryptase is used to determine the likelihood of systemic mastocytosis and mast cell burden in newly diagnosed cutaneous mastocytosis patients. BMP and LFT are routinely checked as a part of the pruritus work-up especially when patients presents with no obvious rash (i.e. eczema plaques); renal and hepatic insufficiency are common causes of pruritus.
Bone marrow biopsy would be indicated in adults presenting with elevated tryptase levels concerning for systemic mastocytosis.
DeWane ME, Waldman R, Lu J. Dermatomyositis: Clinical features and pathogenesis. J Am Acad Dermatol. 2020;82(2):267-281.
Bogdanov I, Kazandjieva J, Darlenski R, Tsankov N. Dermatomyositis: Current concepts. Clin Dermatol. 2018;36(4):450-458.
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