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E1102. Musculoskeletal Sarcoidosis: A Radiological Footprint
Authors
  1. Laura Marsland; King's College Hospital NHS Foundation Trust
  2. Dennis Bielecki; King's College Hospital NHS Foundation Trust; King's College London
Background
Sarcoidosis is a chronic granulomatous disease in which non-caseating granulomata develop in organs in response to environmental and genetic factors. It is ubiquitous, both in the sense that it is prevalent throughout the world and that it can occur in almost any organ in the body. Thoracic sarcoid disease is considered universal, contributing most significantly to mortality associated with sarcoidosis, however musculoskeletal manifestations affect a third of patients, symptoms ranging from mild arthralgia to profound joint deformation and disability. As a disease process, sarcoidosis is the master of non-specificity. Histopathology, signs, symptoms, and radiological features are shared with numerous illnesses which can lead to delays in diagnosis and effective treatment. This exhibit reviews the radiological features of musculoskeletal sarcoidosis, compares them to those of other diseases and aims to enable the reader to recognize a distinct radiological footprint.

Educational Goals / Teaching Points
To provide an overview of sarcoidosis as a multi-system disease, including pathophysiology and epidemiology. To describe the multi-modality radiological features of musculoskeletal sarcoidosis in bone, joint and muscle and to offer a framework to differentiate from other disease processes. To introduce the role of PET/CT imaging in diagnosis and monitoring of sarcoidosis. To illustrate the topic with cases.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Musculoskeletal manifestations of sarcoidosis are considered according to radiological presentation in bone, joint and muscle. Bone: The osteolytic lesion is the hallmark of bone sarcoidosis and has a wide differential, including primary and secondary bone malignancy and infection. While certain radiological appearances can offer clues, the key to differentiating the sarcoid lesion is location. Sarcoid lesions tend to affect the appendicular skeleton, most commonly the small bones of the hands, in which lace-like bone loss and subcortical tunneling occur. Joints: Sarcoid arthropathy most commonly presents acutely. The classic triad of acute arthralgia, hilar lymphadenopathy and erythema nodosum in Lofgren Syndrome is recognisable. Chronic sarcoid arthropathy may be distinguished from other chronic arthropathic process, such as rheumatoid arthritis, by the notable absence of joint erosions. Muscles: Sarcoid myopathy exists as either acute, chronic or nodular subtypes. While the clinical presentation and biochemical and electrophysiological findings might be non-specific, MR and PET/CT imaging has been shown to offer a degree of diagnostic sensitivity.

Conclusion
Musculoskeletal manifestations of sarcoidosis may present with non-specific clinical and radiological appearances. However, knowledge of the pattern of multimodality radiological features (or the 'radiological footprint') can support the radiologist to offer a confident diagnosis and/or comprehensive assessment of disease progression. PET/CT offers the opportunity to improve the sensitivity and specificity of radiological diagnosis and monitoring in sarcoidosis and there may be scope for this role to expand with increased availability.