An examination of the synergy of pain and PTSD on quality of life: additive or multiplicative effects?

Although models have been proposed to explain common factors that maintain comorbid pain and PTSD [Sharp TJ, Harvey AG. Chronic pain and posttraumatic stress disorder: mutual maintenance? Clin Psychol Rev 2001; 21: 857-77], the exact nature of the relationship between these two conditions and their impact on quality of life (QOL) is unknown. The aim of the present investigation was to examine the unique and interactive effects of PTSD and pain on role functioning and life satisfaction--two important domains of QOL. The study utilized a help-seeking sample of motor vehicle accident (MVA) survivors whose accidents resulted in symptoms of comorbid PTSD and pain (N=192). Hierarchical regression models were used to examine the relationship between four PTSD symptom clusters, pain, and the interaction of each cluster and pain on role functioning and life satisfaction separately. Results of these analyses revealed a significant interaction of pain and emotional numbing on role functioning, suggesting a multiplicative effect on this domain of QOL. Decomposition of this interaction revealed a negative association between numbing and functioning at low levels of pain but no relationship at higher levels. A marginal interaction of pain and hyperarousal also was noted for life satisfaction. Decomposition of the interaction effect revealed a marginal association between hyperarousal and decreased satisfaction only at high levels of pain. A main effect of emotional numbing on decreased life satisfaction also was observed in this model, suggesting a unique influence of numbing. The results of the current research indicate that the synergistic relationship of pain and PTSD may vary across domains of QOL.