Polymyalgia rheumatica patients presenting with atypical clinical features still exhibit characteristic ¹⁸F-FDG...

The utility of ¹⁸F-fluorodeoxyglucose positron emission tomography with low-dose computed tomography (¹⁸F-FDG PET/CT) to diagnose patients with atypical features but clinically confirmed PMR is unknown. This study explored ¹⁸F-FDG PET/CT findings among atypical PMR cases and contrasted results with a typical PMR population. The performance of an AI model for PMR diagnosis was also tested.

Natural language processing searched the electronic data warehouse at our institution for ¹⁸F-FDG PET/CT reports with PMR findings. Medical record review confirmed the clinical diagnosis for potential cases. Required entry Criteria of the 2012 EULAR/ACR Classification for PMR (age ≥50 years, bilateral shoulder aching and abnormal CRP and/or ESR) stratified patients as "typical" or"atypical". Qualitative and semi-quantitative (SUV_max) scoring of ¹⁸F-FDG uptake at characteristic musculoskeletal sites was undertaken for steroid-naïve, atypical PMR patients and compared with results for steroid-naïve, typical cases from an earlier study. A ResNet50 AI model was tested on the atypical cohort's images, with GradCam maps generated and cross-checked by an experienced clinician.

225 ¹⁸F-FDG PET/CT reports were retrieved from >38,000 scans; 121 patients had a clinical PMR diagnosis. Seventeen steroid-naïve, atypical cases were compared with 35 steroid-naïve, typical patients. The frequency of abnormalities at key musculoskeletal sites was similar between groups, however mean SUV_maxwas significantly higher in the typical cohort. The AI model identified a PMR diagnosis in 16/17 (94.1%) atypical patients.

Characteristic findings of PMR are appreciated on ¹⁸F-FDG PET/CT among atypical patients, but avidity is reduced. AI technology can reliably detect this imaging pattern. Words: 249 _{(max. 250)}.