P048 A zosteriform masquerader: a rare cutaneous involvement of multiple myeloma while on treatment

Abstract

Multiple myeloma (MM) is a clonal plasma-cell malignancy characterized by the production of monoclonal immunoglobulins (Behera B, Pattnaik M, Sahu B et al. Cutaneous manifestations of multiple myeloma. Indian J Dermatol 2016; 61: 668–71; Hina M, Naviwala SS, Shabbir-Moosajee M et al. Recurrent cutaneous manifestation in multiple myeloma. BMJ Case Rep 2024; 17: e260485). Extramedullary involvement is uncommon, and cutaneous manifestations are particularly rare. Recognition of such lesions is important as they often signify advanced disease and carry prognostic significance. A 51-year-old woman diagnosed with MM had completed 10 cycles of chemotherapy (lenalidomide, bortezomib and dexamethasone) and zoledronic acid. Subsequently she was started on daratumumab, dexamethasone and pomalidomide in view of persistent disease activity. During this treatment, she developed multiple firm, erythematous–violaceous, nontender nodules and plaques over the pubic region and left thigh extending up to the knee involving multiple dermatomes. Differential diagnoses included herpes zoster, cutaneous metastasis and leukaemia cutis. Dermoscopy showed multiple whitish and reddish globules with faint reticular pigment network on a reddish brown background. Histopathology revealed epidermal atrophy and diffuse infiltration of plasma cells in the dermis. Plasma cells showed pleomorphism with coarse stippled chromatin and increased mitosis. Immunohistochemistry was positive for CD138, CD56, MUM1 and kappa in situ hybridization. The final diagnosis was cutaneous plasmacytoma. Cutaneous plasmacytomas occur in < 2% of patients with MM. They are associated with high tumour burden, relapse or treatment-resistant disease. Zosteriform distribution is extremely uncommon and may clinically mimic herpes zoster or metastases along dermatomes. Early biopsy is essential, as cutaneous disease may alter prognosis and treatment planning. New or atypical skin lesions in MM should prompt urgent biopsy. Zosteriform cutaneous MM, although rare, may signal disease progression. Dermatologist–oncologist collaboration is crucial for timely diagnosis and management.