Clinical Images: A rare and misleading condition: isolated skeletal involvement of Erdheim–Chester disease

Abstract

The patient, a 60-year-old woman with osteoporosis, complained of pain in the right ankle, which spread to the perimalleolar region, and then the left ankle. No fractures were detected on the radiograph; magnetic resonance (MR) imaging showed bone edema in the cuboid–calcaneal bone heads and the left distal metadiaphyseal tibia. The patient received nonsteroidal anti-inflammatory drugs, analgesics, and bisphosphonates for suspected complex regional pain syndrome, without benefit. Given the persistent pain at the tibias bilaterally, computed tomography (CT) was performed, showing (A) sclerosis of the trabecular bone in the distal third of the tibial diaphysis; (B and C) sagittal T1-weighted and STIR MR images showed extensive spongiosa edema in the fourth and fifth segments of both tibial diaphyses, well demarcated by the continuous trabecular bone, with a 7-cm craniocaudal extension; (D) the skeletal scintigraphy confirmed the radiotracer uptake at the upper and lower tibial diaphyses. Given the atypical bone lesions and the unresponsiveness to the treatments administered, a bone biopsy was performed. (E, G, and H) Histologic examination revealed intertrabecular fibrosis and infiltrates of foamy histiocytes, which were (F) diffusely positive for CD163, aspects compatible with Erdheim–Chester disease, a non-Langerhans cell histiocytosis that provokes an abnormal aggregation of histocytes in several organs (cardiovascular and central nervous system, retroperitoneum), including long bones.¹ BRAF (V600E) mutation was detected (via Droplet Digital Polymerase Chain Reaction, allele frequency [AF] 0.06%), and histologic findings supported the diagnosis by excluding other potential mimickers.² A CT scan of the abdomen was negative for pathologic findings; the patient was then advised to start the BRAF inhibitor vemurafenib.

We thank Professor Marco Pizzi for providing the histologic images.