1. An Overview of the Emerging Evidence on PTSD in ICD-11
Chris Brewin
Clinical Educational & Health Psychology
University College London
and Camden & Islington NHS Foundation Trust

2. Objectives for ICD-11 PTSD
Identify core features from knowledge of what symptoms are unique to and predictive of PTSD Make these core features of the disorder more explicit, so as to (a) simplify diagnosis (b) reduce qualifying combinations of symptoms (c) reduce comorbidity (d) provide a meaningful contrast with DSM-5 (e) facilitate clinical utility and scientific research Add impairment criterion to address possible over-leniency of ICD-10

3. Proposed definition of PTSD in ICD-11
This disorder follows exposure to an extremely threatening or horrific event or series of events. It consists of 3 core elements: (a) Reexperiencing: vivid intrusive memories, flashbacks, or nightmares that involve reexperiencing in the present, accompanied by fear or horror; (b) Avoidance: marked internal avoidance of thoughts and memories or external avoidance of activities or situations reminiscent of the traumatic event(s); (c) Hyperarousal: a state of perceived current threat in the form of hypervigilance or an enhanced startle reaction. The symptoms must also last for several weeks and interfere with normal functioning

4. Diagnosing PTSD in ICD-11
No formal stressor criterion – clinician can use own judgement on what is extremely threatening or horrific. May include events that are subthreshold for DSM-5 (e.g. delusional threats to life experienced in psychotic or drug-induced states) provided there is an appropriate subjective reaction Requires one symptom indicating reexperiencing in the present either during the day or at night (or an emotional reaction to a trauma reminder if there is no explicit memory); one symptom indicating either internal or external deliberate avoidance; one symptom indicating either hypervigilance or enhanced startle reaction Symptoms are fewer in number but more specific

5. Evaluating PTSD in ICD-11
How well does the proposed three-factor structure fit the data? What is the prevalence of PTSD under ICD-11 compared to other systems? Are the same people diagnosed under ICD-11 compared to other systems? What are the rates of comorbidity under ICD-11 compared to other systems? Does ICD-11 diagnose cases of similar severity to other systems?

6. Factor structure
West Papuan refugees (Tay et al., 2015): 3-factor ICD-11 model had better fit than a variety of DSM models Injury patients six years post-trauma (Forbes et al., 2015): 3-factor ICD-11 model had excellent fit but 2 factor model was nonsignificantly better. One other study (Haravuori et al., 2016) supports a 2-factor structure, the product of a very high correlation between re-experiencing and avoidance in these samples Over 60s several decades post-trauma (Glück et al., 2016): 1, 2, and 3-factor models fit the data very well. One index of model fit favoured the 1-factor model but three alternative indices favoured the 3-factor model.

7. Factor structure
Seven independent trauma samples (Hansen et al., 2015): ICD-11 3-factor structure had excellent fit (except in incest victims) - fit was better than the DSM-5 4-factor structure and alternative 5-factor and 6-factor DSM-5 models, all of which fit the data poorly. The ICD-11 structure was invariant over men and women In a sample of former German political prisoners, using the Impact of Event Scale - Revised to model ICD-11 PTSD, the three-factor model provided an excellent representation of the data, but a one-factor model and the two-factor model of Forbes et al. (2015) were rejected as poor representations of the data (Hyland et al., 2017)

8. Prevalence
In 9/14 samples of adults there was a statistically higher prevalence for DSM-IV or DSM-5 PTSD than ICD-11 PTSD (between 2% and 12%) In 1/5 samples of children and adolescents (the only treatment-seeking sample) there was a statistically higher prevalence for DSM than ICD-11 PTSD (15%) The criteria for re-experiencing and hyperarousal are more stringent (specific) in ICD-11 whereas the criteria for avoidance are more stringent in DSM-IV In 11 samples of adults there was 74%-97% agreement between ICD-11 and DSM on presence or absence of a PTSD diagnosis. In 5 samples of children/adolescents the agreement was 65%-97% Overlap in PTSD cases was 53% (55% for DSM-IV vs DSM-5: Hoge et al. 2014)

9. Comorbidity and validity
Compare those meeting criteria for ICD-11 PTSD but not DSM PTSD with those meeting criteria for DSM PTSD but not ICD-11 PTSD: In 4/4 studies less MDD comorbidity under ICD-11; 1 study showed less comorbidity with fear and distress disorders under ICD-11 Some suggestion that pure ICD-11 cases associated with higher levels of impairment (Stein et al., 2014), or higher levels of trauma exposure in children (Haravuori et al., 2016) Taxometric analyses both using DSM-IV and ICD-11 formulations of PTSD replicated the dimensional solution previously found for DSM-IV, but suggested a categorical solution for ICD-11 (Kliem et al., 2016)

10. Conclusions from 34 empirical reports from four continents
Factor structure of ICD-11 generally fits the data well and outperforms the DSM in several comparisons. This is partly because its structure is simpler and was informed by previous factor analyses. There may be some specific samples (accident victims, incest survivors) where the fit is not so good In adults PTSD prevalence rates according to the DSM-IV, DSM-5, and ICD-11 formulations are generally comparable although there is consistent evidence for slightly lower rates of PTSD in adults under ICD-11. ICD-11 is markedly more stringent than ICD-10 In children and adolescents there is little evidence for any difference in prevalence rates (at least in community samples). ICD-11 identifies quite a lot of cases missed by DSM-5. The simpler formulation may be particularly appropriate here.

11. Conclusions from 34 empirical reports from four continents
When stringent comparisons are made there is consistent evidence of less comorbidity between PTSD and depression under ICD-11 than DSM criteria. This was a primary aim of ICD-11 A taxometric analysis has suggested that cases and non-cases are more distinct in ICD-11 rather than existing on a continuum. This is potentially very helpful for studies of biological markers Overall ICD-11 PTSD is associated with a comparable clinical profile and comparable severity but identifies a slightly different group of individuals. Although DSM-IV and DSM-5 identify more cases than ICD-11, there are some cases uniquely identified by ICD-11 and not DSM-5. This raises important questions for both diagnostic systems about who are in the non-overlapping groups, whether they would attract other (different) diagnoses, and whether they have different clinical needs

12. General references
Brewin, C.R. (2013). “I wouldn’t start from here”: An alternative perspective on PTSD from ICD-11. Journal of Traumatic Stress, 26, 557–559.
First, M. B., Reed, G. M., Hyman, S. E., & Saxena, S. (2015). The development of the ICD-11 clinical descriptions and diagnostic guidelines for mental and behavioural disorders. World Psychiatry, 14,
Friedman, M.J. (2013). Finalizing PTSD in DSM-5: Getting here from there and where to go next. Journal of Traumatic Stress, 26, 548–556.
Maercker, A. et al. (2013). Proposals for mental disorders specifically associated with stress in the ICD-11. Lancet, 381,
Maercker, A. et al. (2013). Diagnosis and classification of disorders specifically associated with stress: New proposals for ICD-11. World Psychiatry, 12, 198–206.
Reed, G. M. (2010). Toward ICD-11: Improving the clinical utility of WHO's International Classification of Mental Disorders. Professional Psychology-Research and Practice, 41,