A40-36 Benign Metastasizing Leiomyomatosis Presenting With Recurrent Pneumothoraces and a Miliary Pattern of Pulmonary Nodules

Abstract Benign metastasizing leiomyoma (BML) is a rare condition, with fewer than 200 documented cases globally. It is characterized by the extrauterine spread of histologically benign uterine smooth muscle tumors, most commonly to the lungs, and their growth is estrogen dependent. Pulmonary involvement manifests as multiple well-circumscribed nodules and is often discovered incidentally in women with a history of uterine leiomyoma. A miliary pattern is a rare manifestation of BML, with only three cases previously described. This pattern poses significant diagnostic challenges, as it may mimic infectious or malignant pulmonary processes. Although most patients remain asymptomatic, some may develop respiratory complications including pneumothoraces. We describe a rare case of BML in a woman presenting with recurrent spontaneous pneumothoraces and a diffuse miliary pattern of pulmonary nodules. A 30yo woman with a history of uterine fibroids with prior myomectomy presented to an outside hospital with one week of worsening dyspnea. Chest x-ray revealed a large left pneumothorax requiring urgent chest tube placement. Subsequent CT imaging revealed innumerable pulmonary nodules. An infectious and autoimmune workup, including TB interferon gamma assay were unrevealing. The patient had worsening of her pneumothorax despite ongoing conservative measures and she was transferred to our center for further management. Due to the question of infection and unknown etiology of the nodules she underwent bronchoscopy with bronchoalveolar lavage and transbronchial biopsy of the lingula demonstrating fragments of leiomyoma. Because of her persistent pneumothorax, she underwent a subsequent VATS with mechanical pleurodesis and wedge biopsy that again confirmed the presence of leiomyomas. She was seen by gynecology with a plan to start on GnRH agonist therapy after discharge. She returned one month after discharge with a recurrent left-sided secondary spontaneous pneumothorax requiring repeat chest tube placement. Due to persistence of the pneumothorax she again underwent VATS, this time with talc pleurodesis and successful lung re-expansion. This illustrates an unusual presentation of BML with a diffuse miliary pattern of pulmonary nodules and recurrent pneumothoraces, features rarely reported in the literature. The diagnosis was established through histopathologic and immunohistochemical confirmation of smooth muscle differentiation with estrogen and progesterone receptor positivity. This demonstrates the importance of considering BML in the differential diagnosis of diffuse pulmonary nodules in young women with a history of uterine leiomyomas. It adds to the limited literature on the spectrum of BML presentations and highlights the potential for serious respiratory complications and the importance of long-term monitoring. This abstract is funded by: None