Patient reported outcomes and joint tenderness at three months-follow up better predict long term pain than baseline characteristics – an early rheumatoid arthritis cohort study

Abstract

Objective: To investigate pain course over time and to identify baseline and 3-month predictors of unacceptable pain with or without low inflammation in early RA.Methods: A cohort of 275 patients with early RA, recruited in 2012-2016, was investigated and followed for 2 years. Pain was assessed using a visual analogue scale (VAS; 0–100 mm). Unacceptable pain was defined as VAS pain >40 based on the patient acceptable symptom state (PASS), and low inflammation as CRP <10 mg/l. Baseline and 3-month predictors of unacceptable pain with or without low inflammation, respectively, were evaluated using logistic regression analysis. Results: Mean pain improved significantly from inclusion to 3 months, but was thereafter essentially unchanged. After 2 years, 32% had unacceptable pain. Out of these patients 81% had low inflammation. More and stronger associations were found for 3-month predictors of unacceptable pain with or without low inflammation at 1 and 2 years, compared with baseline predictors. Three-month predictors of these pain states at 1 and 2 years were higher pain, higher patient global assessment, higher score for the health assessment questionnaire, and having at least 2 more tender joints than swollen joints. No significant associations were found for objective inflammatory measures. Conclusion: A substantial proportion of patients had unacceptable pain with low inflammation after 2 years. This emphasizes the non-inflammatory pain spectrum in early RA. Three months after diagnosis is a good time-point for assessing the risk of long-term pain. Worse patient reported outcomes at 3-months follow-up were associated with increased risk of long-lasting pain, whereas no such associations were found for objective inflammatory measures, further strengthening the uncoupling between pain and inflammation in RA. Having at least 2 more tender joints than swollen joints was associated with future unacceptable pain, supporting this measure as a tool for predicting long-term pain.