A Rare Case of Erdheim-Chester Disease and Langerhans Cell Histiocytosis Overlap Syndrome.

A 48-year-old woman with a past medical history of seizures and end-stage renal disease secondary to obstructive uropathy from retroperitoneal fibrosis presented to the emergency department with seizures and altered mental status. A Glasgow Coma Scale of 4 prompted intubation, and she was subsequently admitted to the intensive care unit. Magnetic resonance imaging of the brain performed to elucidate the aetiology of her seizure showed a dural-based mass within the left temporoparietal lobe as well as mass lesions within the orbits. Further imaging showed extensive retroperitoneal fibrosis extending to the mediastinum with involvement of aorta and posterior pleural space. Imaging of the long bones showed bilateral sclerosis and cortical thickening of the diaphyses. Imaging of the maxillofacial structures showed osseous destructive lesions involving the mandible. These clinical and radiological features were consistent with a diagnosis of Erdheim-Chester disease; however, the patient's skin biopsy was consistent with Langerhans cell histiocytosis.