Diagnostic accuracy of 18F-FDG PET-CT scores in distinguishing polymyalgia rheumatica from other inflammatory rheumatic diseases: a multicentre retrospective study (RHUMATEP).

PURPOSE: To evaluate the diagnostic accuracy of 18F-FDG PET-CT-based scores to differentiate polymyalgia rheumatica (PMR) from other inflammatory rheumatic diseases.

METHODS

This retrospective multicentre study included 232 patients with inflammatory rheumatic diseases (150 PMR, 50 axial spondylarthritis AxSpA and 32 other rheumatic diseases) divided into training and external validation cohorts. The gold standard final diagnoses were those that were upheld by an experienced rheumatologist, at least at 6 months' follow up, taking into account all available information (clinical data and evolution, radiological, biological, PET-CT) but blinded for the scoring system. 18F-FDG uptake at 29 anatomical sites was assessed using visual analysis and maximum standardized uptake value (SUVmax). Several scoring systems previously described in the literature were evaluated for PMR and AxSpA: Leuven and Leuven/Groningen, Besançon and Pean de Ponfilly scores; Heidelberg and Saint-Étienne algorithms for PMR; sacroiliac-to-sacrum ratio (SIJ/S) for AxSpA. A new Brest score was also developed based on the best performing sites (AUC ≥ 0.8) identified in the training cohort. Diagnostic performance was assessed for each score and algorithm.

RESULTS

The highest diagnostic accuracy for PMR was observed with the Leuven, Leuven/Groningen, Besançon and Brest scores (AUC 0.83-0.89 in training and 0.67-0.69 in external validation cohorts). The Leuven/Groningen sensitivity and specificity were respectively 94.7%/67.9% (training) and 72.2%/55.2% (validation). The sensitivity of Pean de Ponfilly score was lower (78.9% (training) and 55.6% (validation)). The diagnostic performance of Brest was quite similar to Leuven scores (96.4%/66% in training; 86.1%/51.7% in validation). Heidelberg and Saint-Étienne algorithms demonstrated high sensitivity with low specificity.

CONCLUSION

Leuven/Groningen and Brest scores may represent promising tools for distinguishing PMR from other rheumatic diseases, given their ease of use and diagnostic performance.