Associations of interleukin-6 with vegetative but not affective depressive symptoms in terminally ill cancer patients

Purpose: Previous studies have reported associations of depressive symptoms with pro-inflammatory cytokines, especially with interleukin-6 (IL-6) in noncancer subjects and cancer patients. Meanwhile, symptoms such as tiredness and appetite loss may be vegetative symptoms of depression when associated with other diagnostic criteria of depression. Such vegetative-type symptoms worsen during the last 6 months of life in cancer patients and may not be associated with affective depressive symptoms such as sadness and nervousness. This study explored associations between depressive symptoms and plasma IL-6 in terminally ill cancer patients whose survival period was confirmed to be less than 6 months by follow-up, with attention to differences in vegetative and affective depressive symptoms. Methods: Data from 112 consecutively recruited terminally ill cancer patients who registered at a palliative care unit without any active anticancer treatment were used. Plasma IL-6 levels were measured using an electrochemiluminescence assay. Depressive symptoms included in the DSM-IV and Cavanaugh criteria were assessed by structured interviews and were categorized into affective symptoms and vegetative symptoms. Affective symptoms were also measured with the depression subscale of the Hospital Anxiety and Depression Scale, which does not include vegetative symptoms. Results: Vegetative symptoms, such as appetite loss, insomnia, and fatigue, were significantly associated with IL-6 levels. However, neither of the affective symptoms nor their severity was associated with IL-6 levels. Conclusions: IL-6 was associated with vegetative depressive symptoms in terminally ill cancer patients but not with affective depressive symptoms, suggesting possible differences in the pathophysiological mechanisms between these sets of symptoms.