EMG measured reaction time as a predictor of invalid symptom report in psychosomatic patients

Background: Symptom validity tests (SVTs) and performance validity tests (PVTs) are important tools in sociomedical assessments, especially in the psychosomatic context where diagnoses mainly depend on clinical observation and self-report measures. This study examined the relationship between reaction times (RTs) and scores on the Structured Inventory of Malingered Symptomatology (SIMS). It was proposed that slower RTs and larger standard deviations of reaction times (RTSDs) would be observed in participants who scored above the SIMS cut-off (>16). Methods: Direct surface electromyography (EMG) was used to capture RTs during a computer-based RT test in 152 inpatients from a psychosomatic rehabilitation clinic in Germany. Correlation analyses and Mann-Whitney U were used to examine the relationship between RTs and SIMS scores and to assess the potential impact of covariates such as demographics, medical history, and vocational challenges on RTs. Therefore, dichotomized groups based on each potential covariate were compared. Results: Significantly longer RTs and larger RTSDs were found in participants who scored above the SIMS cut-off. Current treatment with psychopharmacological medication, diagnosis of depression, and age had no significant influence on the RT measures. However, work-related problems had a significant impact on RTSDs. Conclusion: There was a significant relationship between longer and more inconsistent RTs and indicators of exaggerated or feigned symptom report on the SIMS in psychosomatic rehabilitation inpatients. Findings from this study provide a basis for future research developing a new RT-based PVT.