Waldenstrom's macroglobulinemia (WM) is lymphoplasmacytoid malignancy that affects B lymphocytes. Cutaneous involvement of WM is rare, but various cutaneous manifestations have been reported. These findings are due to various pathological processes including direct invasion of tumor cells into the skin, deposition of paraproteins, hyperviscosity syndrome, and cryoglobulinemia. A 64-year-old man presented with a 10-day history of pruritic erythematous papules and plaques on his trunk and elbows. The clinical features were suspicious for eczematous dermatitis. However, treatments such as oral antihistamines, topical steroids, ultraviolet light therapy and immunomodulators (dapsone and cyclosporine) were minimally effective. The patient's hemoglobin decreased gradually, and he was referred to the department of hematology. Serum electrophoresis exhibited a monoclonal peak in the β1 region. The diagnosis of WM was established based on a bone marrow biopsy that revealed 80% lymphoplasma cellularity, staining positive for CD20 and CD79a. However, there was no direct infiltration of tumor cells or immunoglobulin deposition on the skin biopsy. After the patient started rituximab, cyclophosphamide and dexamethasone therapy, anemia and neutropenia gradually improved. His pruritus also markedly subsided. Although there was no evidence of infiltration of WM in the skin lesions, they were thought to be strongly associated with monoclonal gammopathy. This dermatologic feature has not been documented as a nonspecific cutaneous manifestation of WM or monoclonal gammopathy. To clarify the association between intensely pruritic papules/plaques and WM, more reports and further studies could be needed.
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