Background: Cytokines of the innate immune response may contribute to behavioral alterations that resemble major depression as manifested in medically healthy individuals.
Methods: To explore potential similarities and differences between cytokine-induced depression and idiopathic major depression in healthy subjects, dimensional analyses comparing specific symptom dimensions of depression were conducted in 20 patients with malignant melanoma administered the innate immune cytokine, interferon (IFN)-alpha, and 28 medically healthy subjects with major depression of similar age and gender distribution. The Hamilton Rating Scale for Depression was used to assess severity of individual depressive symptoms.
Results: Severity of symptoms of anxiety, depressed mood, and impaired work/activities were comparable between patients with IFN-alpha-induced depression and medically healthy depressed patients. Interestingly, however, compared to medically healthy patients with major depression, patients with IFN-alpha-induced depression reported significantly greater psychomotor retardation and weight loss and significantly less severe feelings of guilt.
Limitations: The relatively small sample size limited statistical power to detect small differences in symptom expression among groups.
Conclusions: The data suggest that there is considerable overlap in symptom expression between cytokine-induced depression and idiopathic depression in medically healthy subjects. Nevertheless, differences in isolated symptom domains suggest that cytokines may preferentially target neurocircuits relevant to psychomotor activity (e.g. basal ganglia), while having a limited effect on cognitive distortions regarding self-appraisal.