Diagnostic Challenges in Disseminated Mycobacterium szulgai Infection: A Case Report in the Setting of Advanced HIV Infection.

Mycobacterium szulgai is a rare, slow-growing non-tuberculous mycobacterium (NTM), accounting for less than 0.2% of NTM isolates worldwide. It most often presents with pulmonary disease resembling tuberculosis, while disseminated infection is exceptionally uncommon and typically occurs in immunocompromised hosts. We report a 34-year-old male newly diagnosed with advanced HIV infection who presented with painful cutaneous nodular lesions, intermittent fever, anorexia, and significant weight loss. Initial investigations suggested cutaneous nocardiosis or fungal infection, with cultures yielding Aspergillus niger and Corynebacterium species. Despite antifungal and antibacterial therapy, his condition progressed to multifocal cutaneous lesions, oral mucosal involvement, and osteomyelitis of the tibia and fibula. An extended microbiological evaluation of a bone biopsy revealed acid-fast bacilli, and cultures identified M. szulgai via rpoB gene sequencing and matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry (MS). Further imaging and bronchoalveolar lavage confirmed disseminated infection involving lungs, skin, and bone. The patient was treated with rifampicin, ethambutol, and moxifloxacin in combination with antiretroviral therapy. After six months, complete resolution of cutaneous lesions, regression of pulmonary nodules, and normalization of inflammatory markers were achieved. Therapy was planned for 12-18 months. This case underscores the diagnostic complexity of disseminated M. szulgai infection in advanced HIV. Initial misinterpretation as nocardiosis or fungal disease delayed diagnosis, highlighting the importance of extended microbiological workup when conventional therapies fail. Definitive identification through molecular sequencing and MALDI‑TOF MS was crucial. The patient's favorable response to a rifampicin‑based multidrug regimen emphasizes the need for early recognition and prolonged therapy. This report contributes to the limited literature on disseminated M. szulgai and reinforces the importance of considering atypical mycobacteria in immunocompromised patients.