Purpose: To evaluate the use of (18)F-FDG PET/CT for the assessment of tocilizumab (TCZ) as first-line treatment in patients with polymyalgia rheumatica (PMR).
Methods: Patients with PMR were prospectively enrolled in a multicentre clinical trial assessing TCZ therapy (the TENOR trial). The patients underwent FDG PET/CT at baseline, after the first infusion of TCZ (TCZ 1) and after the last infusion of TCZ (TCZ 3). Responses to treatment were evaluated in terms of the PMR activity score (PMR-AS), and the C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) laboratory tests. Maximal standardized uptake value (SUVmax) was used for assessment of FDG uptake in regions usually affected in PMR (spinous processes, hips, shoulders, sternoclavicular region and ischial tuberosities). The Wilcoxon test was applied to evaluate the changes in parameters after the infusions and Spearman's rank correlation test was applied to assess the correlations between SUVmax and PMR-AS, CRP and ESR.
Results: Of 21 patients included in the trial, 18 were evaluated. The median bioclinical parameter values decreased after TCZ 1 (PMR-AS from 38.2 to 15.7, CRP from 65.2 to 0.4 mg/l and ESR from 49 to 6.5 mm; all p < 0.05) as did the median SUVmax (from 5.8 to 5.2; p < 0.05). All values also decreased after TCZ 3 (PMR-AS from 38.2 to 3.9, CRP from 65.2 to 0.2, ESR from 49 to 2, and SUVmax from 5.8 to 4.7; p < 0.05). In a region-based analysis, all SUVmax were significantly reduced after TCZ 3, except the values for the cervical spinous processes and shoulder regions. With regard to correlations, few significant differences were found between ∆SUVmax and the other parameters including ∆PMR-AS, ∆CRP and ∆ESR in the patient-based and region-based analysis.
Conclusion: FDG uptake decreased significantly but moderately after TCZ therapy in PMR patients, and might reflect disease activity.
Keywords: 18F-FDG PET/CT; Cytokines; Inflammation; Polymyalgia rheumatica; Therapeutic assessment.