Perceived Injustice and Anger in Fibromyalgia with and Without Comorbid Mental Health Conditions: A Hebrew Validation of the Injustice Experience Questionnaire

Objectives: Perceived injustice (PI), assessed by the Injustice Experience Questionnaire (IEQ), is an important trigger of anger. Both PI and anger are associated with adverse chronic pain outcomes, and with comorbid mental health severity. We aimed examined the roles of PI and anger in mediating pain across Fibromyalgia patients, with and without comorbid anxiety/depression (FM+A/D, FM-A/D, respectively), as well as rheumatoid arthritis (RA), and pain-free controls (PFC). We hypothesized the highest levels of PI, anger, and pain in FM+A/D patients, followed by FM-A/D, RA, and PFC, thus also validating a Hebrew version of the IEQ. Methods: We translated the IEQ using the forward-backward method and collected data online. Based on self-reported anxiety/depression, the sample comprised 66 FM+A/D patients, 64 FM-A/D, 34 RA, and 32 PFCs. Assessments included the IEQ, state and trait anger, pain intensity, anxiety, depression, and pain catastrophizing. The structure and reliability of the Hebrew IEQ were examined using factor analysis and Cronbach alpha. Bootstrapped-based modeling was used to test the roles of state and trait anger in mediating and moderating the relationship between PI and pain intensity. Results: We confirmed a one-factor structure of the IEQ, with excellent reliability. FM+A/D patients demonstrated the highest scores in all measures. Within this group, trait anger moderated the mediating effect of state anger in the relationship between PI and pain intensity. Discussion: Our findings validate a Hebrew IEQ and highlight the importance of PI and state and trait anger in the differential manifestation of mental health comorbidity in FM.