Leukocytoclastic vasculitis (LCV) has been reported as a rare paraneoplastic phenomenon associated with several hematologic disorders, including indolent lymphomas such as Waldenström macroglobulinemia. However, there are very few cases of LCV in the context of plasma cell disorders. We present the case of a 58-year-old female who developed a rapidly progressive, ulceronecrotic skin lesion on her left lower leg due to leukocytoclastic vasculitis. The lesion was initially suspected to be an ulcerative chronic wound (ulcus cruris) but represented an atypical manifestation of leukocytoclastic vasculitis as primary and only clinical sign of smoldering multiple myeloma IgG kappa. After standard induction chemoimmunotherapy with daratumumab, bortezomib, lenalidomide, and dexamethasone, the patient proceeded to high-dose chemotherapy with melphalan, followed by autologous stem cell transplantation for consolidation. Despite a bacterial skin superinfection, myeloma treatment was successfully completed without any major complications. The skin lesion healed concurrently with the reduction in paraprotein levels, and there was no need for plastic surgical intervention. LCV mimicking ulcus cruris can represent a rare and atypical initial manifestation of plasma cell neoplasia. In this case report, systemic myeloma treatment proved to be effective for inducing complete remission of advanced ulceronecrotic skin damage. This case extends the spectrum of reported monocloncal gammopathies of cutaneous significance.