Abstract

Background: Leishmania donovani is the primary causative agent of Visceral Leishmaniasis (VL), but its emergence as a cause of purely Cutaneous Leishmaniasis (CL) is an increasing challenge to public health. Conventional diagnosis relies on microscopic identification of amastigotes, a method that frequently fails in pauciparasitic lesions. Case Presentation: We report the case of a 60-year-old Caucasian female, who presented with a persistent, non-healing, non-painful ulcer on her right mid-arm with positive travel history to Spain. Despite a high clinical suspicion for Cutaneous Leishmaniasis (CL), two separate skin biopsies have failed to detect amastigotes on Giemsa staining, although histology showed non-caseating granuloma. The definitive diagnosis was achieved when tissue from the second biopsy was subjected to Polymerase Chain Reaction (PCR) analysis, which returned a positive result for the Leishmania donovani complex. Systemic workup, including blood Leishmania PCR and rK39 serology, were negative, confirming the absence of visceral involvement. She started Miltefosine 50 mg TDS for 28 days with cessation of her immunosuppressive medication to avoid developing resistance. Conclusion: This case highlights the diagnostic pitfall of relying solely on histopathology for CL, particularly in pauciparasitic and immunosuppressed patients. The failure of two biopsies, contrasted with the definitive molecular confirmation, underscores the critical role high index of clinical suspicion and the PCR as indispensable tool for accurate diagnosis and species identification. This case contributes to the growing evidence of L. donovani causing purely cutaneous disease and advocates for the routine use of molecular diagnostics in challenging leishmaniasis cases.