Polymyalgia rheumatica (PMR) is a systemic inflammatory disease characterized by pain and morning stiffness in the shoulders, pelvic girdle and neck. It mainly affects people aged >50 years and is commonly associated with constitutional symptoms and raised inflammatory markers [1].

Glucocorticoids are the mainstay of the treatment. It usually results in rapid symptom relief. The 2015 European Alliance of Associations for Rheumatology/American College of Rheumatology (EULAR/ACR) collaborative initiative recommends an individualized tapering regimen based on disease activity, glucocorticoid-related adverse events and comorbidity [2]. However, reliable markers for disease activity are lacking and almost half of the patients experience disease relapse during steroid tapering [3]. In clinical practice, assessing disease activity is challenging, as symptoms may be caused by other conditions like osteoarthritis, rotator cuff tendinopathy or steroid myopathy. In case of uncertainty about the disease activity, the physician may unnecessarily delay glucocorticoid tapering or increase the glucocorticoid dose, increasing the risk of glucocorticoid-related toxicity, or incorrectly taper glucocorticoids, impairing the functionality and quality of life of patients. In addition, the lack of reliable, valid, and sensitive outcome measures hampers the evaluation and comparison of the efficacy of glucocorticoid-sparing agents, which are highly needed in PMR.

Leeb and Bird developed a composite score for measurement of disease activity in PMR, called the polymyalgia rheumatica activity score (PMR-AS) [4]. It consists of 5 domains: morning stiffness time (MST), ability to elevate the upper limbs (EUL, 3 = none, 2 = below shoulder girdle, 1 = up to shoulder girdle, 0 = above shoulder girdle), physician's global assessment with a visual analogue scale (VASph), pain as indicated by the patient (VASp) and C-reactive protein (CRP) level. It is calculated as: CRP (mg/dL) + VASp (0–10) + VASph (0–10) + (MST (min)x0.1) + EUL (0–3). PMR-AS values <1,5 indicate remission, <7 low disease activity, 7–17 moderate disease activity, and >17 high disease activity [4,5]. The Inflammatory Joint Disease Working Group of the French Society for Rheumatology found that 9.35 was the best cut-off point for active disease when using the PMR-AS at one time point [6] and that glucocorticoid doses were decreased in most patients in case of PMR-AS <10 [7]. The cut-off point of PMR-AS <10 was afterwards used as part of the primary endpoint in 4 randomized controlled trials [[8], [9], [10], [11]] in PMR patients, whereas in another trial [12] PMR-AS <7 was used. Consequently, there is still no consensus on the optimal cut-off point.

Several glucocorticoid-sparing agents, such as IL-6-, IL-17- or JAK-inhibitors, induce a decrease or normalization of CRP blood level regardless of the disease activity [13,14]. By consequence, when using these agents, CRP is no longer reliable as disease activity measure. Erythrocyte sedimentation rate (ESR)-PMR-AS (with ESR instead of CRP) [4], clin-PMR-AS (same formula without CRP) [15] and imp-CRP-AS (1.12*clin-PMR-AS + 0.26) [15] were developed as alternative scores to circumvent this problem. Previous studies found an excellent agreement and correlation between these scores and the original PMR-AS [4,15,16].

Qualitative studies have shown that physical disability and stiffness have the most important impact on the quality of life of PMR patients [17,18]. In the PMR-AS, physical function is evaluated by scoring the ability to raise the upper limbs on a 0–3 scale. However, this provides a limited view of overall function and inadequately represents this domain [[17], [18], [19]]. Moreover, this is scored by the physician during the consultation and is thereby influenced by the timing of the consultation (morning versus afternoon). In addition, stiffness severity and duration are two separate concepts for patients [[17], [18], [19]]. The duration of morning stiffness is reported to fluctuate daily [17,18], which probably explains the poor test-retest reliability [20]. VAS or numeric rating scale of stiffness severity had a better test-retest reliability [21].

The aim of this study was to determine the optimal cut-off point of the PMR-AS to discriminate between disease remission and active disease both in patients with a recent PMR diagnosis and in patients with established disease. In addition, we wanted to evaluate if substituting the ability to raise the upper limbs by a VAS for functionality and adding a VAS for stiffness besides the duration of morning stiffness could improve the reliability of the existing PMR-AS. Finally, we also wanted to assess the discriminatory capacity of ESR-PMR-AS, clin-PMR-AS and imp-PMR-AS to detect active disease in comparison to PMR-AS.