Abstract
INTRODUCTION: An 82-year-old female presented to the emergency department with presyncope and was found to be bradycardic with proptosis and ophthalmoparesis. MRI revealed an extra-axial enhancing mass compressing the medulla and bilateral enhancing retro-orbital masses. CASE DESCRIPTION: Imaging, including nuclear medicine bone scan, PET CT, and cardiac MRI raised the suspicion for a histiocytic neoplasm. These findings, along with a fibrohistiocytic infiltrate on bone biopsy and a BRAF V600E oncogenic mutation on plasma cell-free DNA confirmed a diagnosis of Erdheim-Chester disease. DISCUSSION: These enhancing masses invoke a broad differential, including a histiocytic or granulomatous process, fungal infection, amyloidosis, IgG4 disease, and lymphoma. Systematic laboratory, radiologic, pathology, and genetic testing yielded a diagnosis of this rare histiocytic disorder with frequent neurologic involvement.