Nocardia wallacei: A rare cause of actinomycetoma in an immunocompetent patient.

Actinomycetoma, a neglected tropical disease affecting the skin and soft tissues, is primarily caused by filamentous bacteria including Nocardia species. Here, we report a healthy 56-year-old man who has a one-year history of nodular lesions with seropurulent discharge on his right knee. Despite negative initial tissue culture, the sulfur granules that were partially acid-fast and Gram-positive branching filamentous rods were revealed in the tissue section. Repeated investigation identified the rare pathogen Nocardia wallacei, using matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) and 16S ribosomal ribonucleic acid (rRNA) gene sequencing. The patient was successfully treated with a six-month course of trimethoprim-sulfamethoxazole.This report describes a rare case of actinomycetoma due to N. wallacei, highlighting the challenges in diagnosis and the importance of accurate pathogen identification for the successful management of infection. The current literature regarding the causative agent will also be discussed.