B73-16 Massive Pleural Effusion by Mycoplasma Pneumoniae in an Immunocompetent Adult

Abstract Introduction Although mycoplasma pneumonia classically manifests as a mild, self-limited respiratory illness, severe complications- including large pleural effusions, empyema, and necrotizing pneumonitis - have been reported in both pediatric and adult populations. While pleural effusions occur in up to 20-25% of adult cases, massive effusion or empyema requiring invasive management is exceedingly rare, particularly in immunocompetent adults. Recognition of these atypical presentations is critical for timely diagnosis and management. Case Presentation An immunocompetent, African American, 34-year-old woman with a history of neurologic and psychiatric comorbidities presented on day 1 with progressive dyspnea, pleuritic discomfort, and reduced exercise tolerance. Initial evaluation revealed a large, unilateral pleural effusion causing near-complete lung collapse. Laboratory studies showed leukocytosis and elevated inflammatory markers. Except for a positive serum mycoplasma pneumoniae IgM, all other serologic tests were negative. Imaging confirmed significant effusion without overt parenchymal cavitation. Over the first 2 days, the patient underwent repeated ultrasound-guided thoracentesis with a removal of 1L of exudative fluid each time. Despite drainage, she continued to demonstrate respiratory compromise. A chest tube was placed for escalating effusion volume. Pleural effusion was exudative with mononuclear predominance and negative cancer cytology. Cultures remained negative throughout the hospital course. Persistent loculations and incomplete lung expansion prompted surgical intervention on the 8th day. The patient underwent fiberoptic bronchoscopy followed by left thoracotomy with extensive lysis of adhesions, visceral pleurectomy, and mechanical decortication. Large quantities of thickened pleura were removed, allowing full re-expansion of the lung. The postoperative course was uncomplicated, and she gradually improved with supportive care and combination antimicrobial therapy targeting mycoplasma. Discussion This case highlights a rare but severe manifestation of M. pneumonia infection in an immunocompetent adult. Massive effusion or empyema requiring thoracotomy is exceedingly uncommon, with only isolated adult cases reported in literature. Current evidence suggests that exuberant host immune responses, rather than direct organism burden, contribute to severe pleural pathology. It is likely that such cases have been underreported in the past due to unreliable serologies and undertesting. This case serves as a reminder for clinicians to remain vigilant for atypical presentations of M. pneumoniae, even though it is a relatively mild pathogen. This abstract is funded by: None