Multisystem Erdheim-Chester disease: A case-based review with emphasis on nuclear imaging and diagnostic challenges

Objective. To illustrate the diagnostic value of hybrid nuclear imaging in Erdheim-Chester disease (ECD) through a detailed case report and literature-based discussion, with an emphasis on imaging hallmarks and diagnostic challenges. Methods. A 65-year-old woman presented with chronic right knee pain. 99mTc-MDP bone scintigraphy and 18F-FDG PET/CT demonstrated symmetric radiotracer uptake in the metaphyseal and diaphyseal regions of femurs and tibias, consistent with the “hot knees” sign. Results. Histological analysis of a bone biopsy revealed foamy histiocytes positive for CD68 and negative for CD1a, confirming the diagnosis of ECD. Hybrid imaging techniques played a critical role in identifying characteristic skeletal involvement, evaluating disease extent, and directing appropriate clinical management. Conclusion. This case highlights the pivotal role of nuclear imaging, particularly hybrid modalities such as PET/CT, in the early recognition and comprehensive assessment of multisystem ECD. Integrating functional and anatomical imaging is essential to improve diagnostic accuracy and optimize patient outcomes in rare systemic histiocytosis.