Whole-body MRI of patients with polymyalgia rheumatica identifies a distinct subset with complete patient-reported response to glucocorticoids

Objectives: To determine whether whole-body MRI defines clinically-relevant subgroups within polymyalgia rheumatica (PMR) including glucocorticoid responsiveness.

Methods: 22 patients with PMR and 16 with rheumatoid arthritis, untreated and diagnosed by consultant rheumatologists, underwent whole-body, multiple-joint MRI, scored by two experts. PMR patients reported whether they felt “back to normal” on glucocorticoid therapy and were followed for a median of 2 years.

Results: All PMR patients were deemed to respond to glucocorticoids clinically. A characteristic pattern of symmetrical, extracapsular inflammation, adjacent to greater trochanter, acetabulum, ischial tuberosity and/or symphysis pubis, was observed in 14/22 of the PMR cases. In PMR, this pattern was associated with complete glucocorticoid response (p=0.01), higher pre-treatment C-reactive protein (CRP) and serum IL-6, and better post-treatment fatigue and function. Only 1/14 in the extracapsular group could stop glucocorticoids within 1 year, compared to 4/7 of the others. A score derived from the five sites discriminating best between PMR and RA correlated with IL-6 (p<0.002). IL-6 levels ≥16.8 pg/mL had 86% sensitivity and 86% specificity for the extracapsular MRI pattern.

Conclusions:

A subset of patients with rheumatologist-diagnosed PMR had a characteristic, extracapsular pattern of MRI inflammation, associated with elevated IL-6/CRP and with complete patient-reported glucocorticoid responsiveness.