Challenges in diagnosing mucocutaneous leishmaniasis caused by Leishmania (Mundinia) martiniquensis mimicking oral histoplasmosis in a patient with advanced HIV disease from Southern Thailand.

Differentiation between leishmaniasis and histoplasmosis remains a significant diagnostic conundrum, especially in immunosuppressed patients, due to overlapping clinical presentations and histopathological features. We report a case of a 53-year-old Thai man with advanced HIV disease from Southern Thailand who presented in 2020 with a chronic palate ulcer and hard palate perforation, initially diagnosed as histoplasmosis and treated with itraconazole for a year. Three years later (2023), the patient developed systemic symptoms, and biopsies confirmed visceral leishmaniasis. Given the increasing number of autochthonous leishmaniasis cases, the patient's original diagnosis from 2020 was reexamined. Retrospective analysis of the original palate biopsy revealed amastigotes with kinetoplasts, whereas PAS and GMS staining were negative for fungi, excluding histoplasmosis. Molecular diagnostics, which combined PCR for Leishmania spp. and Histoplasma capsulatum with Sanger sequencing, confirmed Leishmania martiniquensis and ruled out Histoplasma capsulatum, leading to a corrected diagnosis of mucocutaneous leishmaniasis. This report documents the second case of mucocutaneous leishmaniasis caused by L. martiniquensis in Thailand, with primary mucocutaneous presentation that progressed to visceral involvement. This highlights diagnostic challenges due to morphological similarities between Leishmania amastigotes and Histoplasma capsulatum yeasts, emphasizing the need for integrative histopathological (including specific staining techniques) and molecular diagnostics for accurate diagnosis and effective treatment.