Sarcomatoid Mesothelioma Revealed After Treatment for Tuberculous Pleurisy: A Case Report.

Differentiating tuberculous (TB) pleurisy from malignant pleural mesothelioma is challenging due to similar clinical presentations. We report an 83-year-old man with sarcomatoid mesothelioma initially treated for TB pleurisy. He presented with lymphocyte-predominant exudative pleural effusion and a positive Interferon-Gamma Release Assay. Thoracoscopy revealed purulent effusion, but biopsies were non-diagnostic. Despite empiric anti-tuberculosis therapy, the effusion persisted. A subsequent surgical biopsy showed fibrosis and scattered spindle cells. However, 2 months later, a rapidly growing chest wall mass with bone invasion appeared. A CT-guided percutaneous biopsy showed proliferation of atypical spindle cells and fluorescence in situ hybridization (FISH) analysis allowed for the diagnosis of sarcomatoid mesothelioma. This case highlights the aggressive nature of sarcomatoid mesothelioma and its diagnostic difficulty. For treatment-refractory pleurisy, clinicians must maintain high suspicion, ensuring vigilant follow-up and prompt repeat biopsies despite negative initial results, while consulting pathologists to consider additional FISH testing.