Cognitive Behaviour Therapy for Depersonalisation Derealisation Disorder (CBT-f-DDD): Study protocol for a randomised controlled feasibility trial.

Background: Depersonalisation-Derealisation Disorder (DDD) is a distressing mental health condition which causes individuals to have a sense of 'unreality' or detachment about themselves and/or the world around them. DDD is chronically under-researched, and as a result, under-diagnosed, with a population prevalence of about 1%. In systematic reviews, Cognitive Behavioural Therapy (CBT) has been found to be the only intervention with significant clinical impact on alleviating the symptoms of DDD. However, previous studies have suffered from small sample sizes, reliance on expert clinicians to provide therapy and narrow population demographics. This feasibility randomised controlled trial aims to provide more robust evidence for the treatment efficacy of CBT in DDD.

Methods: The study aims to recruit 40 participants from two NHS trusts, 20 per arm from two community Mental Health NHS services in London. The intervention group will receive 12-24 individual CBT sessions over a 6-month period from CBT therapists following specialist training for DDD. The control group will receive Treatment as Usual. We will assess the feasibility of a future RCT through measuring the acceptability of the intervention, and assessing our ability to recruit, retain and randomise participants. We will calculate the correlation of scores on the Cambridge Depersonalisation Scale, its baseline standard deviation, assess the magnitude/direction of change and characterise the uncertainty in the outcome scores and the probability that the results have been obtained by chance.

Discussion: The outputs of this trial will guide whether a definite RCT is feasible and acceptable, for both the clinician and participant.

Trial Registration: The ISRCTN registration number is ISRCTN97686121(https://doi.org/10.1186/ISRCTN97686121).