Erdheim-Chester Disease: A Case Report Exploring the Crucial Role of Multimodality Imaging and Targeted Specimen Re-review

Erdheim-Chester disease (ECD) is a rare multisystemic, non-Langerhans cell histiocytic neoplasm that is becoming increasingly recognized.The discovery of somatic mutations in the mitogen-activated protein kinase signaling pathway, most commonly BRAF V600E , has led to the disease being reclassified from an inflammatory process to a neoplastic one.The disease often presents with non-specific symptoms, most commonly bone pain, often leading to a delay in diagnosis, with the diagnosis often first being suggested by imaging findings.We present the case of a 56-year-old gentleman who presented with an atypical, five-year prodrome of progressive proximal muscle weakness, fatigue, hyperreflexia, and focal fasciculations, initially mimicking a primary neuromuscular or motor neuron disease.Subsequent multimodality imaging revealed classic features of systemic histiocytosis, including symmetric appendicular osteosclerosis on bone scintigraphy, retro-orbital masses with exophthalmos on brain magnetic resonance imaging, and perinephric soft tissue infiltration ("hairy kidney") and periaortic encasement ("coated aorta") on abdominal computed tomography, alongside primary testicular involvement on positron emission tomography.Although an initial retroperitoneal tissue biopsy yielded non-diagnostic fibroadipose tissue, specimen rereview histopathologically confirmed the BRAF V600E mutation.The patient was initiated on targeted kinase inhibitor therapy with vemurafenib.This report highlights the vital role of multimodality imaging in suggesting the diagnosis and the necessity of expert tissue re-review or molecular sequencing when initial biopsy results appear non-specific.