Test-retest reliability of pain VAS/NRS, stiffness VAS/NRS, HAQ-DI and mHAQ in polymyalgia rheumatica: An OMERACT study.

Objective: To examine the test-retest reliability of four measurement instruments in polymyalgia rheumatica (PMR): pain severity visual analogue scale (VAS) / numerical rating score (NRS), stiffness severity VAS/NRS, the Health Assessment Questionnaire-Disability Index (HAQ-DI) and the modified Health Assessment Questionnaire (mHAQ).

Method: Two prospectively collected datasets were used. All participants had a diagnosis of PMR and only those with stable disease were included in analyses. Measurement instruments were administered twice, with a testing interval of two to six weeks. The intra-class correlation coefficient (ICC) was calculated using a two-way mixed effects model looking for absolute agreement. ICC values of 0.8-0.9 were deemed representative of good test-retest reliability, whilst values >0.9 were representative of excellent test-retest reliability.

Results: From the first dataset, 38 participants were analysed. The ICC between baseline and 2 weeks for pain VAS, stiffness VAS, HAQ-DI and mHAQ were 0.84, 0.82, 0.92 and 0.92 respectively. From the second dataset, 58 participants were included in the analysis for pain NRS, 59 for stiffness NRS and 78 for mHAQ. The ICC between baseline and follow-up for pain NRS, stiffness NRS and mHAQ were 0.80, 0.83 and 0.87 respectively.

Conclusion: Pain severity VAS/NRS, stiffness severity VAS/NRS, HAQ-DI and mHAQ all demonstrate good to excellent test-retest reliability in a PMR patient population.