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 Prof Marco Pizzi for providing the histologic images.

该患者是一名患有骨质疏松症的 60 岁女性，主诉右踝疼痛，疼痛扩散到踝周区域，然后是左踝。X 光片未检测到骨折;磁共振 （MR） 成像显示骰骨-跟骨头和左远端胫骨干骨水肿。患者接受非甾体抗炎药、镇痛药和双膦酸盐治疗疑似复杂局部疼痛综合征，无益处。鉴于双侧胫骨持续疼痛，进行了计算机断层扫描 （CT），显示 （A） 胫骨干远端三分之一处的小梁骨硬化;（B 和 C） 矢状位 T1 加权和 STIR MR 图像显示双胫骨干的第四节和第五节有广泛的海绵状水肿，由连续的小梁骨清晰界定，颅尾延伸 7 cm;（D） 骨骼闪烁显像证实了胫骨上部和下部骨干的放射性示踪剂摄取。鉴于非典型骨病变和对所给予的治疗无反应，进行了骨活检。（E、G 和 H）组织学检查显示小梁间纤维化和泡沫状组织细胞浸润，其中 （F） CD163 弥漫性阳性，与 Erdheim-Chester 病相符，Erdheim-Chester 病是一种非朗格汉斯细胞组织细胞增多症，可引起组织细胞在多个器官（心血管和中枢神经系统、腹膜后）中的异常聚集，包括长骨。检测到 ¹ 个 BRAF （V600E） 突变 （通过液滴数字聚合酶链反应，等位基因频率 [AF] 0.06%），组织学结果通过排除其他潜在的模拟者来支持诊断。² 腹部 CT 扫描的病理结果呈阴性;然后建议患者开始使用 BRAF 抑制剂 vemurafenib。

我们感谢 Marco Pizzi 教授提供组织学图像。