PET imaging of polymyalgia rheumatica: update and future trends

Polymyalgia rheumatica (PMR) is a common immune-mediated inflammatory disease affecting older adults over 50 years of age and is characterized by constitutional symptoms with disabling pain and stiffness. Diagnosis remains challenging as clinical features can overlap with other inflammatory musculoskeletal conditions. 18 F-fluoro-2-deoxy- d -glucose ( 18 FFDG-PET/CT) has emerged as a valuable imaging modality by enabling rapid assessment of the hallmarks of PMR: extracapsular and musculotendinous inflammation at characteristic sites localizing to the shoulders, hips, pelvis, spinous processes and knees. In addition, 18 FFDG-PET/CT has established its utility in identifying concurrent giant cell arteritis (GCA), which can result in serious vascular complications including vision loss and stroke. The diagnostic accuracy of 18 FFDG-PET/CT in both clinical and research settings relates directly to image acquisition and interpretation methods, as such consensus procedural guidelines have been developed to standardize imaging protocols. Recent advancements in PET technology, including long axial field-of-view (LAFOV) PET, dynamic and parametric imaging, radiomics and machine learning models may have potential applications in PMR. Furthermore, advances in the understanding of PMR immunopathology have highlighted potential roles for new imaging targets. Radiotracers targeting macrophages, T cells, fibroblasts, and angiogenesis-related pathways may improve disease characterization and offer insight into the molecular and cellular mechanisms involved in PMR pathogenesis. This review aims to summarize the current trends and future directions in image interpretation, PET technologies and potential targets for radiotracer development.