Derrame Pleural Recorrente de Etiologia Indeterminada: Relato de Caso com Enfoque Diagnóstico e Prognóstico

Pleural effusion is a common manifestation in clinical practice and may be the first indication of benign or malignant diseases. The differentiation between transudate and exudate, according to Light's criteria, is an essential step in the initial evaluation. We present a case of massive and recurrent pleural effusion in a male patient, with insidious evolution, progressive respiratory symptoms and images compatible with pleural neoplasia. The absence of a definitive diagnosis even after extensive investigation demonstrates the clinical challenges in the etiological elucidation of these conditions. The discussion includes relevant diagnostic hypotheses, with emphasis on malignant mesothelioma and pleural carcinomatosis, as well as clinical-laboratory criteria that guide differential reasoning.