Title:
Associations between daily chronic pain intensity, daily anger expression, and trait anger expressiveness: an ecological momentary assessment study.

Abstract:
Links between elevated trait anger expressiveness (anger-out) and greater chronic pain intensity are well documented, but pain-related effects of expressive behaviors actually used to regulate anger when it is experienced have been little explored. This study used ecological momentary assessment methods to explore prospective associations between daily behavioral anger expression and daily chronic pain intensity. Forty-eight chronic low back pain (LBP) patients and 36 healthy controls completed electronic diary ratings of momentary pain and behavioral anger expression in response to random prompts 4 times daily for 7 days. Across groups, greater trait anger-out was associated with greater daily behavioral anger expression (P<0.001). LBP participants showed higher levels of daily anger expression than controls (P<0.001). Generalized estimating equation analyses in the LBP group revealed a lagged main effect of greater behavioral anger expression on increased chronic pain intensity in the subsequent assessment period (P<0.05). Examination of a trait×situation model for anger-out revealed prospective associations between elevated chronic pain intensity and later increases in behavioral anger expression that were restricted largely to individuals low in trait anger-out (P<0.001). Trait×situation interactions for trait anger suppression (anger-in) indicated similar influences of pain intensity on subsequent behavioral anger expression occurring among low anger-in persons (P<0.001). Overlap with trait and state negative affect did not account for study findings. This study for the first time documents lagged within-day influences of behavioral anger expression on subsequent chronic pain intensity. Trait anger regulation style may moderate associations between behavioral anger expression and chronic pain intensity.