CASE REPORT OF MYCOBACTERIUM LENTIFLAVUM IN PLEURAL FLUID OF AN IMMUNOCOMPETENT PATIENT IN A SÃO PAULO HOSPITAL

Nontuberculous mycobacteria (NTM) are recognized as opportunistic pathogens causing pulmonary infections, mainly in individuals with chronic structural lung disease. Mycobacterium lentiflavum is a slow-growing NTM rarely associated with clinical infections, and pulmonary disease caused by this organism is infrequently reported. Identification requires specific methods such as MALDI-TOF, mycolic acid chromatography, or gene sequencing (hsp65, 16S rRNA). Its insidious presentation includes nodular or cavitary infiltrates and bronchiectasis. We report a confirmed case of pleural infection by M. lentiflavum . A 62-year-old white male with COPD, smoking, and hypertension presented to the ED on 25/12/24 with 4 days of dyspnea and productive cough, without fever. Workup revealed a right pleural effusion, with 1300 mL drained. On 04/01/25 he developed thrombosis of the brachial and basilic veins. Chest CT showed a large right pleural effusion with 50% atelectasis of the right lung. Diagnostic thoracentesis on 07/01/25 yielded cloudy, serohemorrhagic exudate with 100 cells (10% neutrophils, 53% monocytes, 36% lymphocytes), ADA 4, negative Gram and AFB smears, negative bacterial culture, and acellular cytology. CT pulmonary angiography (13/01/25) showed bilateral segmental pulmonary embolism. Prostate ultrasound was normal, and abdominal CT showed bilateral nephrolithiasis without lymphadenopathy. A working diagnosis of malignant pleural effusion without defined primary tumor was considered. Tumor markers (CA 19-9, CA 15-3, total PSA, free PSA, alpha-fetoprotein) were normal. The patient remained afebrile, without leukocytosis, and with C-reactive protein <3. On 18/01/25 he was discharged to primary care in good general condition. On 30/04/25 the pleural fluid culture for mycobacteria, processed as BK and confirmed by Instituto Adolfo Lutz, identified Mycobacterium lentiflavum . Contacted by phone, the patient reported regular follow-up at the primary care unit, asymptomatic, afebrile, without dyspnea and without specific medications. Pulmonary infection caused by M. lentiflavum is rare and likely underreported in countries with a low prevalence of NTM. This case highlights the importance of laboratory surveillance and the use of specific diagnostic methods to identify this emerging pathogen, allowing for more precise therapeutic guidance, since the susceptibility profile of M. lentiflavum differs from that of other NTM species. Reports like this are essential to promote clinical and microbiological discussion regarding respiratory infections caused by uncommon microorganisms.