IgG Kappa Multiple Myeloma with Cutaneous Plasmacytoma and Hypereosinophilic Leukocytosis in a Young Patient: A Rare Case Report.

BACKGROUND

Multiple myeloma (MM) is a malignant plasma cell disorder with a median age at diagnosis of 69 years. Its occurrence in individuals younger than 30 years is exceptionally uncommon, accounting for approximately 0.3% of all cases. Classic manifestations include bone pain, anemia, renal dysfunction, and hypercalcemia. Extramedullary disease (EMD), such as plasmacytomas, represents a more aggressive phenotype. Among these, cutaneous plasmacytomas-monoclonal plasma cell infiltrates in the skin-are exceedingly rare.

CASE PRESENTATION: A 27-year-old man presented with fatigue, dysphagia, and widespread violaceous papulonodular skin lesions. Examination revealed pallor, oral ulcers, splenomegaly, and blistering nodules over the trunk and extremities. Laboratory evaluation showed bicytopenia, leukocytosis, hyperproteinemia with a reversed albumin-globulin ratio, and renal dysfunction. Serum protein electrophoresis demonstrated an M-spike, and bone marrow aspiration revealed 32% plasma cells, confirming multiple myeloma. Whole-body PET-CT identified generalized osteolytic lesions involving the calvarium, ribs, vertebrae, and appendicular skeleton. Skin biopsy confirmed cutaneous plasmacytoma. Baseline echocardiography showed mild pericardial effusion with preserved left ventricular function; NT-proBNP was elevated. Renal impairment due to light chain cast nephropathy improved after plasmapheresis and initiation of the VRd regimen [bortezomib, lenalidomide, dexamethasone]. After eight cycles, disease relapse occurred with new subcutaneous nodules. Therapy was escalated to Dara-KCd [daratumumab, carfilzomib, cyclophosphamide, dexamethasone], followed by daratumumab, pomalidomide, and dexamethasone, leading to regression of lesions. The patient continues second-line therapy with reassessment planned after four cycles and consideration for early autologous stem cell transplantation.

CONCLUSION

Cutaneous plasmacytoma with hypereosinophilic leukocytosis in young patients with IgG kappa MM is exceedingly rare. Recognition of such atypical presentations is crucial for early detection of extramedullary disease and timely institution of intensive therapy.