Intelligence and Treatment Outcome of Mentalization-Based Treatment in Borderline Personality Disorder

Mentalization-based treatment (MBT) is an evidence based treatment for patients diagnosed with borderline personality disorder (BPD). Although MBT is effective, on average, for individuals with BPD, there are large individual differences in treatment outcomes. Research on predictors of the treatment effect of MBT, such as intelligence, is needed to determine which treatment is most effective for which 'category' of BPD patients, providing more knowledge about optimal indications.

The study aimed to investigate whether intelligence is associated with MBT outcomes in patients with BPD and exploratively studying the difference between two variants of MBT.

A pre-post intervention design was used to examine the effects of MBT on BPD severity. Personal and social recovery were measured as secondary outcome measures. The association between intelligence and the degree of recovery was examined.

No significant correlation was found between intelligence level and treatment efficacy. In addition, a negative correlation between IQ and personal and social recovery was found, indicating that, as IQ increased, the level of recovery decreased. Secondary subanalyses showed the treatment effect of MBT was large and significant in reducing BPD symptoms (Cohen's d = 1.5) and that there was no significant difference between the 2-day MBT and 3-day MBT programmes in terms of a decrease in BPD severity. However, a significant medium positive correlational relationship was found between intelligence and a decrease in BPD severity level for the 3-day MBT, which was not found for the 2-day MBT programme. This indicates that in the 3-day MBT programme, the higher the IQ, the higher the decrease in BPD severity level.

This study is the first to examine the association between intelligence and the outcome of MBT in BPD patients. It shows that patients with a wide range of intelligence (72-124) can equally benefit from MBT and that effectiveness of MBT was not influenced negatively by lower intelligence. Secondary subanalyses showed that this was particularly evident when the intervention was delivered within the context of a 2-day MBT programme. Nevertheless, further randomized studies are required to ascertain the relationship between IQ and treatment effectiveness, as well as other predictors of MBT outcomes.