Among the 10 categories of personality disorders (PDs), interventions for antisocial and borderline personality disorder are best studied. However, the remaining PDs also pose major problems in everyday health care settings. People affected often additionally present with Axis-I disorders such as substance-related, mood or anxiety disorders, and are among those most difficult to treat. Cluster A PDs (paranoid, schizoid, schizotypal) are of particular significance as some authors argue that they may be part of a continuum of mental disorders and be considered as sub-syndrome of schizophrenia

In the context of Cochrane Collaboration reviews for Cluster A, B and C PDs, exhaustive literature searches were completed to identify the current RCT evidence for PD treatments. Retrievals were assessed and evaluated by two reviewers independently and trials for Cluster A PD were identified.

Only very few (under five) RCTs specifically for Cluster A PDs were identified. Some studies reported on mixed PD samples but it was not always possible to extract data specifically for Cluster A disorders. Participants mostly also suffered from Axis-I disorders. Reported outcomes also focus on Axis-I disorder outcomes or general measures such as overall functioning rather than specific PD symptoms.

The current evidence for psychpathological treatment of Cluster A PD is sparse and does not allow for distinct treatment recommendations. Symptom-driven treatment regimes as suggested by several guidelines are not supported by current evidence.