The impact of tonic immobility reaction on the prognosis of posttraumatic stress disorder.

Tonic immobility is the last defense reaction to entrapment by a predator. In humans, peritraumatic tonic immobility was correlated with PTSD severity and poor response to treatment. This study compared the role of peritraumatic dissociation, panic physical symptoms and tonic immobility as predictors of response to standard pharmacotherapy for PTSD. Thirty-six PTSD patients underwent a naturalistic pharmacological treatment. The Posttraumatic Stress Disorder Checklist - Civilian Version (PCL-C) and the Clinical Global Impressions Severity of Illness item scores (CGI-S) were employed at baseline and endpoint to examine treatment outcome. Peritraumatic reactions were assessed using the Physical Reactions Subscale, the Peritraumatic Dissociative Experiences Questionnaire and four motor questions of the Tonic Immobility Scale. After controlling for confounders, tonic immobility was the best predictor of a poor response to treatment, either considering the PCL-C or the CGI-S scores. Tonic immobility seems to have a greater negative impact on PTSD prognosis than peritraumatic panic or dissociation. Additional translational and clinical research may inform about particular mechanisms underlying tonic immobility and open new avenues for prevention and treatment of PTSD.