SESSION TITLE: Tuesday Medical Student/Resident Case Report Posters SESSION TYPE: Med Student/Res Case Rep Postr PRESENTED ON: 10/22/2019 01:00 PM - 02:00 PM INTRODUCTION: Catamenial pneumothorax (CP) is a rare spontaneous pneumothorax (PTX) that occurs cyclically with menstrual periods. It is part of the spectrum of thoracic endometriosis syndrome (TES) in which ectopic endometrial tissue is implanted in thoracic structures. CASE PRESENTATION: A 36-year-old G0P0 female nurse, presented with worsening right-sided pleuritic chest pain for 6 days. She had a history of stage 4 endometriosis associated with recurrent CP. Her first episode was 4 years ago when she had a large right-sided PTX in association with biopsy proven diaphragmatic endometriosis, treated with a right middle lobe wedge resection and chemical pleurodesis. She had multiple recurrences of PTX requiring repeat pleurodesis and subsequent long-term medical therapy with leuprolide and combination oral contraceptive pills. On examination, she was hemodynamically stable with decreased breath sounds in the right lower lung field. CT chest revealed a moderate volume right PTX, a sub-pleural right lower lobe mass and pleural thickening. She underwent a video-assisted thoracoscopic surgery (VATS) with combination (mechanical and chemical) pleurodesis. Pleural biopsy was negative for endometriosis. Postoperative chest x-rays revealed a resolving pneumothorax. Three days after surgery, the patient was discharged home. DISCUSSION: CP is characterized by collapsed lung, which occurs within 3 days of menstruation onset. The pathophysiology involves deposition of focal endometrial pleural implants migrating during leakage of air from the peritoneal cavity, which subsequently break down during menstruation or hypertrophy in response to hormonal changes. Another plausible theory is vasoconstriction and bronchospasm induced by prostaglandin F2 release during menses leading to alveolar rupture and PTX. Due to the vague symptomatology and limited disease awareness, the diagnosis is often missed or delayed leading to life-threatening complications. Histologically proven thoracic endometriosis is frequently but not always associated with CP. Our patient is unique as she previously had a diaphragmatic endometriosis associated CP and later had a non-TES associated bout of CP. Recent evidence suggests that combination surgical (VATS) followed by medical (GnRH agonist) therapy effectively suppresses CP recurrence. However, our patient suffered multiple recurrences even after both modalities. A combination of mechanical and chemical pleurodesis was attempted in an effort to prevent further recurrences. CONCLUSIONS: TES remains an exceedingly rare condition and very few cases have been reported. Our case is unique given her multiple recurrences and unresponsiveness to guideline directed therapies. Physicians should keep a high level of clinical suspicion for thoracic endometriosis in non-smoking women over 31 years, with a history of pelvic endometriosis, and presenting with recurrent pneumothorax. Reference #1: Junejo SZ, Singh Lubana S, Shina SS, Tuli SS.A Case of Thoracic Endometriosis Syndrome Presenting with Recurrent Catamenial Pneumothorax. Am J Case Rep. 2018 May 17;19:573-576. DISCLOSURES: No relevant relationships by Prasanta Basak, source=Web Response No relevant relationships by Stephen Jesmajian, source=Web Response No relevant relationships by Ahmed Qavi, source=Web Response