Abstract Introduction Mycobacterial spindle cell pseudotumor (MSP) is a rare, benign inflammatory lesion characterized by spindle-shaped histiocytes containing acid-fast bacilli, most often associated with Mycobacterium aviumintracellulare complex (MAC) infection in immunocompromised individuals with advanced HIV/AIDS. Clinically and radiographically, MSP can mimic malignant neoplasms such as Kaposi sarcoma or lymphoma, often leading to diagnostic confusion. To date, fewer than 50 cases of MSP have been documented in the literature. Early recognition is crucial, as management focuses on antimycobacterial therapy and supportive care rather than oncologic treatment. Case Presentation A 29-year-old man with no significant past medical history presented in March 2022 with cough and dizziness. Initial chest radiograph revealed pulmonary infiltrates and laboratory results showed anemia and thrombocytopenia. He was discharged from ER after symptomatic improvement. In July 2022, he was hospitalized with fever and diagnosed with disseminated Mycobacterium Avium-intracellulare (MAI) infection. HIV testing revealed advanced AIDS. He was started on antiretroviral therapy (ART) and antimicrobials. CSF analysis was positive for cryptococcal antigen. He was readmitted in September 2022 with pneumonia and a subsegmental pulmonary embolism, for which anticoagulation was initiated. In February 2023, he presented with progressive dyspnea, hypoxia, and chest pain. Chest CT revealed left lung collapse from an obstructing left main-stem bronchial mass extending into the right bronchus. Bronchoscopy with endobronchial ultrasound (EBUS) revealed friable lesions suspicious for Kaposi sarcoma. The patient was intubated and transferred to a tertiary center for further evaluation where repeat EBUS biopsies demonstrated spindle-shaped histiocytes with numerous acid-fast bacilli but no malignant cells, consistent with MSP associated with disseminated MAC. He underwent serial bronchoscopic debridements and silicone Y-stent placement for airway stabilization. Over subsequent months, the patient’s respiratory function steadily improved. By August 2023, bronchoscopy demonstrated complete resolution of the endobronchial lesions and acid-fast staining was negative. The Y-stent was removed and after completing 12 months of MAC therapy, he remained asymptomatic and resumed normal activities. Follow-up imaging in April 2024 showed marked resolution of prior lesions with a small residual left upper-lobe nodule. Discussion MSP represents a localized granulomatous inflammatory reaction to mycobacterial infection, with spindle-cell morphology that may mimic sarcoma or other malignancies. The pulmonary form of MSP is exceedingly rare, with only a handful of reported cases presenting as obstructive endobronchial masses. Histopathologic confirmation with acid-fast staining is essential to distinguish MSP from Kaposi sarcoma or mycobacterial infection-related malignancy. Management primarily involves prolonged antimycobacterial therapy rather than surgical resection or chemotherapy. This abstract is funded by: None
Sidhu et al. (Fri,) studied this question.