The association between physical morbidity and subtypes of severe depression

Physical illness and depression are related, but the association between specific physical diseases and diagnostic subtypes of depression remains poorly understood. This study aimed to clarify the relationship between a number of physical diseases and the nonpsychotic and psychotic subtype of severe depression.

This is a historical prospective cohort study. The study population consisted of all patients diagnosed with ICD-10 severe depression, either nonpsychotic or psychotic subtype, in Danish psychiatric hospitals between 1994 and 2008. The patients' history of physical disease was assessed using the Danish National Patient Register. Using logistic regression it was investigated whether specific physical diseases were associated with relative increased risk for subsequent development of either the nonpsychotic or psychotic depressive subtype.

A total of 24,173 patients with severe depression were included in the study. Of those, 8,260 (34%) were of the psychotic subtype. A history of the following physical diseases, as opposed to their absence, increased the relative risk for subsequent development of the nonpsychotic compared to the psychotic depressive subtype [adjusted incidence odds ratio (AIOR) nonpsychotic vs. psychotic]: ischemic heart disease (AIOR = 1.3, p < 0.001), hypertension (AIOR = 1.2, p = 0.008), stroke (AIOR = 1.2, p = 0.042) and chronic lower pulmonary disease (AIOR = 1.2, p = 0.005). The total load of physical disease also increased the relative risk of nonpsychotic depression [AIOR = 1.05 (per disease), p = 0.001].

This study revealed that, in severe depression, a history of physical disease increased the relative risk of the nonpsychotic rather than the psychotic subtype.