Subtyping depression in the medically ill by cluster analysis.

Background: There is increasing awareness of the need of subtyping major depressive disorder, particularly in the setting of medical disease. The aim of this investigation was to use both DSM-IV comorbidity and the Diagnostic Criteria for Psychosomatic Research (DCPR) for characterizing depression in the medically ill.

Methods: 1700 patients were recruited from 8 medical centers in the Italian Health System and 1560 agreed to participate. They all underwent a cross-sectional assessment with DSM-IV and DCPR structured interviews. 198 patients (12.7%) received a diagnosis of major depressive disorder. Data were submitted to cluster analysis.

Results: Two clusters were identified: depressed somatizers and irritable/anxious depression. The somatizer cluster included 58.6% of the cases and was characterized by DCPR somatization syndromes (persistent somatization, functional somatic symptoms secondary to a psychiatric disorder, conversion symptoms, and anniversary reactions) and DCPR alexithymia. The anxious/irritable cluster had 41.4% of the total sample and included DCPR irritable mood and type A behavior and DSM-IV anxiety disorders.

Limitations: The study has limitations due to its cross-sectional nature. Further, these findings require additional validation in another sample.

Conclusions: The findings indicate the need of expanding clinical assessment in the medically ill to include the various manifestations of somatization, irritable mood, type A behavior and alexithymia, as encompassed by the DCPR. Subtyping major depressive disorder may yield improved targets for psychosomatic research and treatment trials.