Playing Houdini: The Cyclical Vanishing Act of Thoracic Endometriosis Syndrome

Abstract Thoracic endometriosis syndrome (TES) is a rare condition defined by the presence of endometrial-like tissue within lung parenchyma, pleura, or diaphragm. It can affect up to 6-10% of premenopausal women and typically manifests as severe catamenial symptoms, including pulmonary nodules, pneumothorax, hemothorax, and hemoptysis. Diagnosis is often challenging due to the invasive nature of confirming endometrial implants in the thoracic cavity via thoracoscopy during menstruation. Given these diagnostic challenges, it is suspected that the incidence of TES is underdiagnosed and thus undertreated. A 20-year-old female presented with dyspnea on exertion with pleuritic chest pain for the past 3 years. Her past medical history was notable for asthma, autism spectrum disorder, and gastroesophageal reflux disease. She had had a cholecystectomy in adolescence but denied any thoracic surgeries or chest trauma. Her family history was notable for rheumatoid arthritis and breast cancer. She reported that menarche started at age 13 and was associated with severe dysmenorrhea despite use of oral contraceptive pills. Her shortness of breath and migratory chest pain worsened during menses. Figure 1 shows her presenting chest x-ray and chest CT scan. Her laboratory workup was notable for elevated C-reactive protein to 6.15 mg/dl and peripheral eosinophilia to 0.53 K/µL. Rheumatologic workup was unremarkable. Hematuria was present on urinalysis that was attributed to active menstruation. She underwent diagnostic thoracentesis, revealing a grossly bloody exudative effusion with a lymphocytic predominance, without signs of malignancy or infection. Pleural fluid cytology did not reveal endometrial implants. Clinical suspicion for TES remained high, but the patient declined video-assisted thoracoscopy during menstruation due to its invasive nature. Under the guidance of gynecologic consultation, she underwent pelvic MRI, which showed a small focus of endometriosis along the posterior uterus and a small amount of blood or debris in the pelvis. She was initiated on gonadotropin-releasing hormone therapy with subsequent improvement in dyspnea symptoms and radiographic findings. This is a unique case of TES in a young woman presenting with catamenial bilateral pleural effusions. She was treated empirically for TES, resulting in significant improvement in symptoms. This case highlights the importance of considering TES in the differential diagnosis of recurrent pleural effusions in premenopausal women, particularly when thoracoscopy is not feasible and the yield of pleural fluid cytology is low. The use of ancillary noninvasive testing, including pelvic MRI, and characteristic clinical presentation may support the decision for empiric treatment of TES, potentially improving debilitating symptoms.