Asymptomatic skin lesions as a diagnostic clue in multiple myeloma – A case report

Abstract

Multiple myeloma (MM) is a rare cancer of plasma cells in the bone marrow. Cutaneous plasmacytoma is an uncommon but specific skin lesion in MM with an incidence of 2%. Cutaneous plasma cell infiltration in pre-existing MM is a very rare phenomenon, with approximately 100 cases described in the literature. Here, we report a case of a 61-year-old male who presented with asymptomatic skin nodules and plaques over the chest, abdomen, and back of the trunk for five months. Histopathological examination showed mononuclear cells with moderate cytoplasm and round to ovoid nuclei. Immunohistochemistry showed CD138 and kappa positivity and lambda and CD20 negativity, confirming the diagnosis of cutaneous plasmacytoma. Bone marrow biopsy and immunohistochemistry revealed bone marrow plasmacytosis with kappa light chain restriction. Serum free light chain ratio was 106.61 and fluorescence in situ hybridization showed del 13q. The clinical features and investigations fulfilled the diagnostic criteria for MM, and the patient was started on chemotherapy, following which the skin lesions improved. Development of skin lesions is seen in the advanced stages of MM and is considered a bad prognostic sign. However, they can also be seen as initial manifestations of the disease, as in this case. Hence, meticulous investigations and early diagnosis are of paramount importance.