The Challenge of Differentiating Mixed Histiocytosis: A Case Report.

Langerhans cell histiocytosis (LCH) and Erdheim-Chester Disease (ECD) are two forms of histiocytic disease with some overlapping features. They can have multisystem involvement, which makes it a diagnostic challenge. In this report, we present a patient who was diagnosed with both LCH and ECD over the span of 7 years. A 69-year-old female with a past medical history of hypertension, hyperlipidemia, and diabetes mellitus presented with right ear pressure and was subsequently diagnosed with LCH after a mastoid bone biopsy in 2017. She then underwent mass resection. Two years later, during an abdominal MRI for evaluation of cholestatic disease, a large pericardial effusion with pericardial thinning was discovered. Cardiac MRI was concerning for a soft tissue mass anterior and superior to the right atrium, suggestive of infiltrative processes such as histiocytosis. Seven years after the initial presentation, she underwent a pericardial biopsy that diagnosed ECD. It is important to recognize that even though mixed disease is rare, clinical suspicion needs to be high. This is particularly true for patients with cardiac features that would be atypical in LCH to ensure prompt treatment.