Brief individual psychological intervention for people with probable personality disorder: a multicentre, researcher-masked, randomised, controlled superiority trial in England.

BACKGROUND: Long-term psychological treatments are recommended for people with personality disorder. Brief interventions are increasingly delivered but are of uncertain benefit. We aimed to investigate the effectiveness of a brief individual psychological intervention for people with probable personality disorder over a 12-month period. METHODS: The Structured Psychological Support (SPS) study was a multicentre, researcher-masked, randomised controlled superiority trial, conducted in seven mental health Trusts in England: Avon and Wiltshire Mental Health Partnership National Health Service (NHS) Trust, Central and North West London NHS Foundation Trust, Coventry and Warwickshire Partnership NHS Trust, Derbyshire Healthcare NHS Foundation Trust, Lincolnshire Partnership NHS Foundation Trust, Mersey Care NHS Foundation Trust, and Oxford Health NHS Foundation Trust. Participants were aged 18 years or older and had probable personality disorder identified by meeting a threshold of 4 or more on the Standardised Assessment of Personality Abbreviated Scale. We excluded those who: did not consent; had a co-existing psychotic disorder; or were already receiving psychological treatment. We assessed whether participants met criteria for borderline personality disorder using the Structured Clinical Interview for Axis II Personality Disorders and whether they had co-existing complex post-traumatic stress disorder using the International Trauma Questionnaire. We randomly assigned participants to up to ten sessions of SPS plus treatment-as-usual or enhanced treatment-as-usual (allocation ratio 1·15:1), using an independent remote system. Researchers assessing outcomes were masked to group allocation. SPS comprises up to ten individual sessions of personalised psychological support, which includes psychoeducation and psychological skills derived from evidence-based treatments (dialectical behaviour therapy and mentalisation-based treatment). Sessions were usually delivered on a fortnightly basis by staff with previous experience of working with people with personality disorder. The primary outcome was social functioning at 12 months measured using the Work and Social Adjustment Scale (WSAS). Data were analysed using multilevel mixed effects general linear regression on an intention-to-treat basis. We used multiple imputation to address missing outcomes. We undertook a parallel health economic evaluation, which included cost-effectiveness and cost-utility analyses. People with lived experience were involved in the design of the research and in the writing process. The trial was prospectively registered (ISRCTN13918289) and is now complete. FINDINGS: Between Feb 7, 2023, and Jan 31, 2024, 569 potential participants were referred for study inclusion, 34 were deemed ineligible, 56 declined to participate, and 127 were not approached. 352 potential participants provided consent, of whom 16 were deemed ineligible or withdrew. 336 participants were randomly assigned to either SPS (n=180) or treatment-as-usual (n=156). 251 (75%) participants were female, 75 (22%) were male, and ten (3%) were non-binary or other. The mean age was 34·8 years (SD 13·2; range 18-68) and 281 (84%) participants were White. 152 (84%) participants in the SPS group and 132 (85%) in the control group completed the 12-month follow-up. There was no difference between groups for the primary outcome of WSAS score (standardised coefficient 0·12 [95% CI -2·14 to 2·38]; p=0·92). The probability that SPS is cost-effective was 0·34-0·39. There were 36 serious adverse events affecting 17 participants in the SPS group and 16 in the treatment-as-usual group. None were judged to be related to study procedures. Two study participants died during the 12-month follow period, both in the SPS group. INTERPRETATION: We found no difference in social functioning over the course of 1 year among people offered a brief psychological intervention, and no evidence of cost-effectiveness. These data highlight the importance of improving access to longer-term evidence-based psychological treatment programmes for people with personality disorder. FUNDING: National Institute for Health and Care Research.