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Case Reports

Abstract

We present an uncommon co-occurrence of systemic mastocytosis with multiple myeloma that was preceded by abnormal cutaneous features for several years. A 77-year-old male with a three-year history of diffuse rash was found to have anemia and thrombocytopenia with peripheral monocytosis by his primary care provider. He reported significant fatigue and a 10% unintentional body weight loss over three months. A workup from oncology revealed an elevated free kappa/lambda light chains ratio of 50.41. Bone marrow biopsy demonstrated hypercellular marrow with 3% monoclonal plasma cells and large, atypical mast cell aggregates. Immunohistochemistry staining showed mast cell aggregates were positive for CD2 (weak), CD25 (strong), and mast cell tryptase. He was diagnosed with systemic mastocytosis associated with multiple myeloma and referred to dermatology for his rash. Physical exam was notable for red-brown waxy papulonodules coalescing into plaques over his trunk, back, and groin and a positive Darier sign. Patient-provided photographs confirmed this rash had been present for the last three years. Two punch biopsies demonstrated dermal mastocytosis with positive staining for mast cell tryptase, CD68, and CD117. Inpatient treatment was initiated for multiple myeloma with deferment of therapy for systemic mastocytosis. This case illustrates that cutaneous mastocytosis can provide a clue for clinicians to investigate underlying hematologic malignancy.