Research is lacking on possible subtypes of psychosis in difficult-to-treat patients that require long-term institutionalisation due to a combination of psychosis, substance abuse and problem behaviours after multiple failed treatments.

The aim of this study is to increase our knowledge of this group of patients in order to apply more targeted interventions.

To identify subtypes of psychosis among this group by cluster analysis and compare these subtypes on different clinical variables.

PANSS data was acquired for 117 patients. Separate clusters were identified by using Ward's method of hierarchical cluster analysis, replicating Dolffus et al., 1996 [1], who used this method in a cohort of schizophrenia patients. Subtypes of psychosis were identified using PANSS items. Clusters were compared on several clinical variables, f.e. course of admission.

Four distinct clusters were identified (Fig. 1): (1) a ‘positive cluster’, (2) a ‘mild cluster’, (3) a ‘negative cluster’, and (4) a ‘mixed group’. These clusters are similar to those found by Dolffus et al.

There was a significant association between cluster and co-morbid personality disorder, P < 0.05. No significant association was found between clusters and other clinical variables.

Among difficult-to-treat institutionalised patients four distinct subtypes of psychosis could be identified, comparable to those found in a cohort of schizophrenia patients.

The authors have not supplied their declaration of competing interest.