We describe a 73-year-old Japanese man with papuloerythroderma overlapped with monoclonal gammopathy of undetermined significance (MGUS). Clinically, prominent erythroderma was associated with disseminated pruriginous papules, which were characteristically spared on the axillary and inguinal regions, the cubital and popliteal fossae as well as abdominal and small positional folds. Histopathologically, there was a significant perivascular infiltrate of lymphohistiocytic cells intermingled with eosinophils in the upper dermis. A biochemical profile revealed the presence of immunoglobulin G κ chain type monoclonal protein in the serum but the absence of hematological neoplasms. We diagnosed the patient as papuloerythroderma with MGUS, and treated him with narrow-band ultraviolet B and topical steroid. His skin changes were improved, but the sharp γ-globulin peak remained in the electrophoresis of serum protein. This case suggests an association between papuloerythroderma and MGUS.
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