Localized Myofascial Inflammation by Magnetic Resonance Imaging in Recent-Onset Polymyalgia Rheumatica and Effect of Tocilizumab Therapy

Objective To assess the prevalence of myofascial inflammatory lesions visible by magnetic resonance imaging (MRI) and their changes after tocilizumab therapy in active polymyalgia rheumatica (PMR). Methods We conducted a post hoc analysis of data from the TENOR study of tocilizumab monotherapy in PMR. The 18 patients each received tocilizumab injections at weeks 0, 4, and 8. The shoulder and pelvic girdles were assessed at baseline then at weeks 2 and 12 using T1- and T2-STIR-weighted MRI. Radiologists blinded to patient data assessed each muscle group for localized myofascial inflammation on baseline, week-2, and week-12 MRIs. Reproducibility was estimated by having two radiologists assess the week-2 MRIs of 13 patients then computing the kappa coefficient. Results For myofascial lesion detection, intraobserver reproducibility was almost perfect (κ =0.890) and interobserver reproducibility was substantial (κ =0.758). At baseline, all patients had at least one inflammatory myofascial lesion; sites involved were the shoulder in 10 (71.4%) patients, hip in 13 (86.7%), ischial tuberosity in 9 (60.0%), and pubic symphysis in 12 (80.0%). Sites involved at week 12 were the shoulder in 8 (53.3%) patients, hip in 5 (33.3%), ischial tuberosity in 1, and pubic symphysis in 3 (20.0%). At week 12, of 103 muscle groups studied in all, 43 (41.7%) had no inflammatory lesions, compared to 33 at baseline (P=0.002); improvements were noted in 66 (64.1%) muscle groups, worsening in 2 (1.9%), no change in 35 (34.0%) (P=0.034). Conclusion Localized myofascial inflammatory lesions are common in recent-onset PMR and improve during tocilizumab therapy.