C80-04 Inside the Bronchus: Discovering Rosai-Dorfman Disease in Unlikely Locations

Abstract Introduction Rosai-Dorfman disease (RDD) is a rare histiocytic proliferative disorder which predominantly affects the lymph nodes and skin. Even more rarely seen are manifestations of RDD in other organ systems such as the CNS or respiratory tract. Often presenting with non-specific symptoms and mimicking other neoplasms, RDD poses diagnostic challenges. Description of Case Our patient is a 42-year-old female with complex past medical history including uveitis, necrotizing vasculitis (thought to be sarcoid granulomatosis vs polyarteritis nodosa) for which she is on infliximab infusions, lupus anticoagulant, pulmonary capillaritis, avascular necrosis of the hips, and migraines who was admitted for expedited workup to explain her one month of worsening headaches, painful blurry vision, and fatigue. MRI Brain showed 5 new extra-axial CNS lesions with a radiologic differential diagnosis including meningioma, sarcoidosis, dural metastases, and lymphoma. CT Chest showed a new small intraluminal nodular lesion in the LLL bronchus, for which Pulmonary was consulted. Her only respiratory symptom was intermittent dry cough, which was worse at night, and associated with high-pitched expiratory sound. Bronchoscopy was performed revealing a polypoid-appearing LLL lesion (see image), with EBUS-TBNA pathology results notable for polypoid fragments of granulation tissue with lymphoplasmacytic and neutrophilic inflammation, without neoplastic cells, thought to represent a reactive process. Of note, immunohistochemistry showed CD163-positive histiocytes. As lung findings were non-diagnostic, further workup was pursued. Lumbar puncture showed negative culture, no malignant cells, oligoclonal bands, and elevated IL-2. Ultimately, right craniotomy with biopsy of the extra-axial lesions demonstrated dense fibroconnective tissue with mixed inflammatory cell infiltrate containing a focal histocyte-rich region. There was presence of emperipolesis with CD163 and S100-positive cells, which was diagnostic of Rosai-Dorfman disease. Given the concordant immunohistochemistry findings in the endobronchial lesion, this likely represents a case of RDD with pulmonary and CNS involvement. Based on next-generation sequencing of the lesion showing KRAS mutation, the patient was started on targeted therapy with cobimetinib (MEK inhibitor), with which her dural lesions substantially improved on follow-up imaging. Her endobronchial lesion remains stable on CT. She also received prednisolone drops for anterior uveitis. Discussion Rosai-Dorfman disease with CNS and endobronchial involvement is exceedingly rare. This patient had known concomitant autoimmune conditions, which can be associated with multisystem RDD. RDD in the airway can span from the larynx to the bronchi, mimic malignant neoplasms, and cause obstruction. Like other extranodal disease, airway RDD requires histopathology for definitive diagnosis. This abstract is funded by: None