[¹⁸F] FDG uptake in patients with spondyloarthritis: correlation with serum inflammatory biomarker levels

We aimed to evaluate the correlation between 2-deoxy-2-[¹⁸F]fluoro-D-glucose (FDG) uptake and disease activity assessed by serum inflammatory biomarker levels in patients with spondyloarthritis (SpA).

A total of 36 SpA patients (24 untreated and 12 treated) were examined using FDG positron emission tomography (PET)/computed tomography and classified into axial SpA (axSpA) and peripheral SpA (pSpA). FDG uptake was evaluated in 23 regions of the body and scored as follows: 0 = less than liver uptake; 1 = more than or equal to liver uptake; and 2 = more than or equal to twice liver uptake. A score of 1 or 2 was considered positive. The number of positive regions and the total score were counted in each patient. The maximum standardized uptake value (SUVmax) was calculated for each region, and maximum SUVmax (MaxSUVmax) was used as a representative value. Correlation of PET findings with serum inflammatory biomarker levels, including C-reactive protein (CRP), erythrocyte sedimentation rate, and matrix metalloproteinase 3 (MMP-3), was analyzed.

All but two patients had at least one positive lesion. PET indices correlated significantly with most of the serum inflammatory biomarker levels in untreated SpA, but not in treated SpA. Further, MaxSUVmax, number of positive regions, and total score correlated significantly with CRP (all P values < 0.001), and the number of positive regions (P = 0.012) and total score (P = 0.007) correlated significantly with MMP-3 in untreated pSpA. PET indices did not correlate with any serum inflammatory biomarker level in untreated axSpA.

FDG uptake in untreated pSpA correlated significantly with serum inflammatory biomarker levels.