When It's Not Just "That Time of the Month": Identifying Thoracic Endometriosis in the Context of Recurrent Pleural Effusion

Recurrent hemorrhagic pleural effusion presents as a challenge for both the clinician and the patient, with common causes being tuberculosis, malignancy, and collagen vascular diseases. Among uncommon causes of recurrent hemorrhagic effusion is catamenial hemothorax, which is a part of thoracic endometriosis syndrome (TES). Endometriosis is the extrauterine growth of endometrial glands and stroma. It is relatively common among women of reproductive age-group, with reported incidence of around 11%. Although rare, the thorax is the most common extraabdominal site for endometriosis. Here we present a rare case of recurrent hemorrhagic pleural effusion due to thoracic endometriosis in a young female with infertility. A 33-year-old female housewife presented with dyspnea on exertion modified Medical Research Council (mMRC) grade 2 and dry cough occasionally for 6 months. She had a history of tubercular cervical lymphadenopathy for which she was on treatment. Therapeutic thoracocentesis was performed thrice in 4 months. Routine microscopy showed predominantly lymphocytes, mesothelial cells, and numerous foamy histiocytes, some pigment laden. There were no malignant cells or acid-fast bacilli (AFB) detected in the fluid. Pleural fluid amylase and lipase were normal. Contrast-enhanced computed tomography (CT) thorax showed moderate right-sided pleural effusion without any evident parenchymal lesions, pleural lesions, or mediastinal lymphadenopathy. Ultrasonography (USG) abdomen and pelvis showed mild ascites which was nontappable. As we had not reached a definitive diagnosis, medical thoracoscopy was performed. It showed moderate hemorrhagic pleural fluid in the pleural cavity and a small raised erythematous glandular tissue on the parietal pleural surface from which biopsy was taken. Histopathology showed an island of endometrial stroma with a single gland. Immunohistochemistry was performed on this section, which was PAX8 and CD10 positive, confirming the diagnosis of thoracic endometriosis. Pleurodesis with talc slurry was done to prevent further refilling of the effusion. Gynecology opinion was sought, and patient was started on monthly subcutaneous injections of gonadotropin-releasing hormone (GnRH) analogue for 3 months. Chest X-ray after 3 months showed no refilling of pleural effusion. Catamenial hemothorax is the second commonest manifestation of TES, occurring in approximately 14% of cases. It affects the right side in about 80% of the cases. Diagnosis is based on high degree of suspicion and is often delayed. Video-assisted thoracic surgery (VATS) remains the gold standard for diagnosis and management of TES. Medical thoracoscopy is a viable alternative in resource-poor settings or when diagnosis is not confirmed. On histology, diagnosis is confirmed by the presence of endometriotic glands or stroma, which may also show stromal arterioles, erythrocytes, and pigmented histiocytes. In difficult-to-diagnose cases, CD10 immunohistochemical staining can help in diagnosis of endometrial tissue. There are various treatment modalities considered in the management of catamenial hemothorax, like surgical resection, medical management along with pleurodesis, combination therapy, or in some cases, simple observation. Currently, VATS with GnRH analogue therapy is considered the gold standard of management.