French validation of the tonic immobility scale in patients with post-traumatic stress disorder

Abstract

Introduction: Tonic immobility (TI) in humans is characterized by muscle inhibition, hypertonia and analgesia that may occur during a traumatic event. TI is associated with an increased risk of severe and treatment-resistant post-traumatic stress disorder (PTSD). To date, there is no French validated scale for TI. Methods: We studied the face validity (qualitative study) and psychometric properties concerning a French version of the 10-item Tonic Immobility Scale (FR-TIS) in adult with PTSD. Results: Concerning face validity, six participants confirmed that the FR-TIS was simple, clear, and comprehensible, but has some limitations concerning the recall according to age of trauma, peritraumatic dissociation intensity, avoidance behaviors, the type and the context of the trauma. For psychometric properties, 120 patients completed a computerized version of the FR-TIS. FR-TIS showed good psychometric properties in a three-dimensional form with 8 items (Root Mean Square Error of Approximation (RMSEA) = 0.056) including 4 items for TI (Cronbach's α = 0.76), 2 items for fear (Cronbach's α = 0.63), 2 items for dissociation (Cronbach's α = 0.68). Conclusion: The FR-TIS is a potentially useful and easy-to-use tool in clinical practice, to help improving screening and assessment of TI