Tonic immobility during sexual assault – a common reaction predicting post‐traumatic stress disorder and severe depression

Introduction Active resistance is considered to be the ‘normal’ reaction during rape. However, studies have indicated that similar to animals, humans exposed to extreme threat may react with a state of involuntary, temporary motor inhibition known as tonic immobility. The aim of the present study was to assess the occurrence of tonic immobility during rape and subsequent post-traumatic stress disorder and severe depression. Material and methods Tonic immobility at the time of the assault was assessed using the Tonic Immobility Scale in 298 women who had visited the Emergency clinic for raped women within 1 month of a sexual assault. Information about the assault and the victim characteristics were taken from the structured clinical data files. After 6 months, 189 women were assessed regarding the development of post-traumatic stress disorder and depression. Results Of the 298 women, 70% reported significant tonic immobility and 48% reported extreme tonic immobility during the assault. Tonic immobility was associated with the development of post-traumatic stress disorder (OR 2.75; 95% CI 1.50–5.03, p = 0.001) and severe depression (OR 3.42; 95% CI 1.51–7.72, p = 0.003) at 6 months. Further, previous trauma history (OR 2.36; 95% CI 1.48–3.77, p < 0.001) and psychiatric treatment history (OR 2.00; 95% CI 1.26–3.19, p = 0.003) were associated with the tonic immobility response. Conclusions Tonic immobility during rape is a common reaction associated with subsequent post-traumatic stress disorder and severe depression. Knowledge of this reaction in sexual assault victims is important in legal matters and for healthcare follow up.