In the latest version of the DSM, the DSM-5, ¹ a dissociative subtype of post-traumatic stress disorder (PTSD) is included. Patients with this dissociative subtype meet the full criteria for PTSD and, in addition, show persistent or recurrent symptoms of dissociation. These symptoms may take the form of depersonalisation, i.e. experiences of feeling detached from one's body (e.g. like watching yourself from the outside); and/or derealisation, i.e. experiences of unreality of surroundings (e.g. the world around you is experienced as unreal or dreamlike). The addition of this dissociative subtype was partly based on the neurobiological finding that patients with the dissociative subtype of PTSD show midline prefrontal inhibition of limbic regions that are involved in emotion regulation, leading to emotional overmodulation. ^{Reference Lanius, Vermetten, Loewenstein, Brand, Schmahl and Bremner2}

With respect to the clinical implications of the addition of the dissociative subtype to the DSM, it was assumed that patients with the dissociative subtype of PTSD, on the basis of these impaired emotion regulation capacities, are not indicated for trauma-focused treatments (TFTs) such as prolonged exposure (PE) or eye movement desensitisation and reprocessing (EMDR) therapy. ^{Reference Lanius, Brand, Vermetten, Frewen and Spiegel3} These TFTs typically activate the fear network and are aimed at emotional processing of trauma-related information within that network. For patients with the dissociative subtype of PTSD, it was assumed that the ability to adequately activate the fear network would be limited owing to emotional overmodulation, and that, as a result, TFT could not be effective. ^{Reference Lanius, Vermetten, Loewenstein, Brand, Schmahl and Bremner2} Instead, clinicians were advised to provide these patients with a phase-based treatment approach, in which they learn to better regulate their emotions before they enter TFT. ^{Reference Lanius, Vermetten, Loewenstein, Brand, Schmahl and Bremner2} Correspondingly, many clinicians hesitate to provide TFT to individuals with PTSD who have dissociative symptoms. ^{Reference Becker, Zayfert and Anderson4} Presumably, this contraindication would apply even more to patients with severe mental illness, for instance, PTSD patients with psychotic disorder such as schizophrenia and schizoaffective disorder. These disorders are characterised by delusions, hallucinations, disorganised speech, disorganised behaviour and negative symptoms. Although dissociation and psychosis are related and are interactive symptom domains, ^{Reference O'Driscoll, Laing and Mason5} the typical characteristic of severe impairment in reality testing in psychosis is not a feature of dissociation. Having clinically relevant dissociative symptoms in addition to psychotic symptoms may lead to even more reservations among clinicians regarding the use of TFT in these patients. Thus far, however, there is a lack of clinical studies into the effects of TFT on patients with the dissociative subtype of PTSD in patient populations with severe mental illness.

Results

We found that 24.1% of our population fulfilled the criteria of the dissociative subtype, a proportion comparable with other studies. ^{Reference Lanius, Brand, Vermetten, Frewen and Spiegel3} All patients fulfilled diagnostic criteria for a psychotic disorder (60.2% had schizophrenia and 29.6% schizoaffective disorder) and full diagnostic criteria for PTSD. Most patients had experienced severe childhood trauma. In the PTSD, dissociative subtype group, 7 patients dropped out (26.9%) v. 17 patients (20.7%) in the PTSD no-dissociative subtype group (χ²(1, n = 108) = 5.08, P = 0.59). The following analyses were performed in the subgroup of completers (n = 82; post-treatment data were missing for 2 treatment completers). Patients with the dissociative subtype of PTSD showed a similar decrease in PTSD symptoms on the CAPS (within-group Cohen's d = 1.63) to that of the patients without the dissociative subtype of PTSD (within-group Cohen's d = 1.68), with large reductions observed in both groups (see Fig. 1). Patients with the dissociative subtype of PTSD showed significantly more severe PTSD symptoms at pre-treatment (t(80) = −0.29, P = 0.005), whereas at post-treatment, CAPS scores did not significantly differ (t(80) = −1.34, P = 1.85).

Fig. 1 CAPS (clinician-administered post-traumatic stress disorder scale) scores for patients with (n = 18, 22%) and without (n = 64, 78.0%) dissociative subtype in completers.