Persistent pain and its predictors after starting anti-tumour necrosis factor therapy in psoriatic arthritis: what is the role of inflammation control?

Abstract

Objective While considerable focus has been placed on pain due to inflammation in psoriatic arthritis (PsA), less is reported on pain despite inflammation control. Here, we aimed to investigate the occurrence/predictors of persistent pain, including non-inflammatory components, after starting anti-tumour necrosis factor (anti-TNF) therapy. Method Bionaïve PsA patients starting a first anti-TNF therapy 2004–2010 were identified (South Swedish Arthritis Treatment Group register; N = 351). Outcomes included unacceptable pain [visual analogue scale (VAS) pain > 40 mm], and unacceptable pain despite inflammation control (refractory pain; VAS pain > 40 mm + C-reactive protein < 10 mg/L + ≤ 1 swollen joint of 28), assessed at 0, 3, 6, and 12 months. Baseline predictors were estimated by logistic regression. Results Upon starting anti-TNF therapy, 85% of patients reported unacceptable pain, falling to 43% at 3 months and then remaining stable. After 12 months, refractory pain constituted 63% of all unacceptable pain. Higher baseline VAS pain/global, worse physical function and lower health-related quality-of-life were associated with a higher risk of unacceptable/refractory pain at 12 months. More swollen joints and higher evaluator’s global assessment were associated with a lower risk of 12-month refractory pain. Conclusions A substantial proportion of PsA patients reported unacceptable pain throughout the first anti-TNF treatment year. At 12 months, refractory pain constituted about two-thirds of this remaining pain load. More objective signs of inflammation at anti-TNF initiation were associated with less future refractory pain. This highlights insufficient effect of biologics in patients with inflammation-independent pain, warranting alternative treatments.