Comparison and validation of FDG-PET/CT scores for polymyalgia rheumatica

OBJECTIVES: To compare and validate the diagnostic accuracy of FDG-PET/CT scores for polymyalgia rheumatica (PMR); and to explore their relationship with clinical factors.

METHODS: This retrospective study included 39 consecutive patients diagnosed with PMR and 19 PMR comparators. The final clinical diagnosis was established after 6 months follow-up. Patients underwent FDG-PET/CT prior to glucocorticoid treatment. Visual grading of FDG uptake was performed at 30 anatomic sites. Three FDG-PET/CT scores (one by Henckaerts, two by Sondag) and two algorithms (by Flaus and Owen) were investigated. Receiver operating characteristic (ROC) analysis with area under the curve (AUC) was performed. Diagnostic accuracy was assessed at predefined cut-off points.

RESULTS: All three FDG-PET/CT scores showed high diagnostic accuracy for a clinical diagnosis of PMR in the ROC analysis (AUC 0.889 to 0.914). The Henckaerts Score provided a sensitivity of 89.7% and specificity of 84.2% at its predefined cut-off point. A simplified Henckaerts Score showed similar diagnostic accuracy as the original score. The Sondag Scores showed limited specificity at their predefined cut-off points (i.e. 47.4% and 63.2%), while ROC analysis suggested that substantially higher cut-off points are needed for these scores. The Owen and Flaus Algorithms demonstrated high sensitivity, but lower specificity (i.e. 78.9% and 42.1%, respectively) for PMR. Female sex and presence of large vessel vasculitis were associated with lower FDG-PET/CT scores in patients with PMR.

CONCLUSION: The Henckaerts Score showed the highest diagnostic utility for PMR. A modified, concise version of the Henckaerts Score provided similar diagnostic accuracy as the original score.