C78-33 Malignant Pleural Mesothelioma Presenting as Recurrent Pleural Effusions: A Case Report

Abstract Introduction Malignant pleural mesothelioma (MPM) is an aggressive neoplasm arising from mesothelial cells of the pleura. It is strongly associated with asbestos exposure, typically manifesting 20 to 40 years after initial exposure. MPM carries a poor prognosis, with median survival often less than a year in advanced cases. The majority of patients are male, reflecting historical exposure patterns in high risk industries such as construction, shipbuilding, and asbestos manufacturing. Diagnosis is frequently delayed due to nonspecific symptoms, radiologic overlap with other pleural diseases, and the limited sensitivity of pleural fluid cytology. Tissue acquisition through thoracoscopy is often required for definitive diagnosis. Case Presentation A 65 year old woman with a 40 pack year smoking history and a previously biopsied benign 14 mm right lower lobe pulmonary nodule presented with progressive dyspnea. A follow up computed tomography (CT) scan revealed a new moderate right pleural effusion with associated atelectasis. CT angiography ruled out pulmonary embolism but confirmed a large effusion causing complete right lower lobe collapse and partial middle lobe collapse. Thoracentesis removed 1100 mL of exudative fluid; cytology was negative for malignancy. Two additional thoracenteses over the next two weeks removed 1600 mL and 1800 mL, respectively, with persistent lymphocytic exudate and negative cytology. Repeat CT demonstrated multiple pleural-based nodules and thickening along the right pleura and fissure, concerning for malignancy.The patient denied direct occupational asbestos exposure but reported living on a naval base and renovating an older home three decades earlier. Given persistent unexplained effusions, medical thoracoscopy was performed, multiple pleural biopsies were obtained, and an indwelling pleural catheter was placed. Histopathology confirmed malignant pleural mesothelioma. Discussion This case illustrates the diagnostic challenges of MPM in the absence of a classic exposure history. Recurrent lymphocytic exudative effusions with negative cytology warrant a high index of suspicion. Cytology has a limited diagnostic yield and high false negative rate. In contrast, medical thoracoscopy exceeds 90% diagnostic yield and offers both diagnostic and therapeutic benefits. MPM should be considered in the differential diagnosis of unexplained pleural effusions regardless of exposure history. Early thoracoscopic evaluation can expedite diagnosis, guide multidisciplinary management, and improve care for patients with this aggressive malignancy. This abstract is funded by: None