Recurrent low back pain patients demonstrate facilitated pronociceptive mechanisms when in pain, and impaired antinociceptive mechanisms with and without pain.

Abstract

Low back pain (LBP) has been inconsistently associated with enhanced pronociceptive and impaired antinociceptive mechanisms. It remains unknown whether alterations are causal, consequential, or coincidental to pain presence. This study investigated pronociceptive and antinociceptive mechanisms in recurrent LBP (RLBP) patients across painful and pain-free periods, compared with age/sex-matched asymptomatic controls. During a painful episode (day 0) and when pain-free (day 28), 30 RLBP patients were assessed and compared with 30 controls over the same timeframe. Pressure pain thresholds were recorded bilaterally on the arm, back, and leg. Cuff algometry was used to assess cuff pressure pain detection threshold and cuff pain tolerance threshold on the lower legs, as well as temporal summation of pain (10 repeated painful cuff test stimuli on the dominant leg scored on a visual analogue scale) and conditioned pain modulation ([CPM]: cuff pain detection/tolerance threshold on dominant leg, before vs during painful cuff conditioning on the contralateral leg). Recurrent LBP patients displayed reduced pressure pain thresholds at the arm and back on day 0 compared with day 28 (P < 0.047) and with controls on day 0 (P < 0.049). Cuff pain detection threshold was reduced, and ratings of suprathreshold test stimuli were increased in RLBP patients on day 0 compared with day 28 (P < 0.02). Temporal summation of pain magnitude (increase in visual analogue scale scores) was enhanced in RLBP participants on day 0 compared with day 28 (P = 0.027) and with controls on day 0 (P = 0.039). Conditioned pain modulation magnitude (increased threshold during conditioning) was lower overall in RLBP participants than in controls (P = 0.021). Enhanced pronociceptive mechanisms were observed in RLBP patients. When pain-free, measures returned to similar levels as controls, except for CPM, which remained impaired.