Late-onset isolated cutaneous histoplasmosis after autologous stem cell transplant in high-risk kappa light-chain myeloma with del(17p13)

Vollständiger Abstract

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Abstract Histoplasmosis is a dimorphic fungal infection caused by Histoplasma capsulatum, which exists as mycelia-producing infectious microconidia in the environment and as budding yeasts in host tissues. Its clinical presentation ranges from asymptomatic pulmonary infection to life-threatening disseminated disease particularly in immunocompromised individuals. Cutaneous histoplasmosis is rare and typically reflects dissemination rather than isolated involvement. Opportunistic infections following autologous stem cell transplantation (ASCT) usually occur in the first year; presentations beyond 3 years are uncommon. We describe the case of a 55-year-old man with high-risk κ light-chain multiple myeloma with del(17p13), diagnosed in 2018. The disease was initially refractory to bortezomib, lenalidomide and dexamethasone but responded to salvage therapy with PAD (bortezomib, doxorubicin, dexamethasone) and VTD-PACE (bortezomib, thalidomide, dexamethasone, cisplatin, doxorubicin, cyclophosphamide and etoposide). He subsequently underwent ASCT with high-dose melphalan in February 2022 and achieved complete remission with measurable residual disease negativity. He was maintained on bortezomib–lenalidomide. In April 2025, 38 months post-ASCT, the patient presented with progressively increasing erythematous nodules and plaques on the chin, scalp and legs, without systemic symptoms. Dermoscopy suggested dermal granulomas, and biopsy revealed numerous intracellular yeast forms on periodic acid–Schiff and Gomori methenamine silver stains, consistent with H. capsulatum. Immunohistochemistry confirmed plasma cell polytypia, excluding plasmacytoma. Bone marrow measurable residual disease (MRD) remained negative, positron emission tomography–computed tomography showed no systemic involvement and fungal culture confirmed H. capsulatum. He was treated with oral itraconazole (200 mg three times daily for 3 days, followed by 200 mg twice daily), with marked lesion regression within 4 weeks. Treatment was planned for 12–18 months and he remained clinically stable. This case illustrates that opportunistic fungal infections can occur late after ASCT, even in patients in remission with MRD negativity. Cutaneous lesions in patients who are post-transplant should not be assumed to represent malignancy relapse without histopathological confirmation. Biopsy with fungal stains and culture is essential for diagnosis and timely antifungal therapy leads to favourable outcomes. Our report adds to the limited literature on late-onset histoplasmosis after ASCT and underscores the need for continued long-term vigilance in the transplant recepients.