Cortisol response to experimental pain in patients with chronic low back pain and patients with major depression

OBJECTIVE: Chronic pain and major depression have been associated with alterations of the hypothalamus-pituitary-adrenal axis (HPA) activity. Previous studies suggested that HPA activity is diminished in chronic pain but increased in depression. However, little is known about the effects of experimentally induced acute pain on cortisol secretion in patients with chronic pain and depression.

METHODS: On three different occasions (day 1, day 8, day 90), we repeatedly examined 20 patients with chronic low back pain without depression, 22 patients with major depression without pain, and 33 healthy subjects using heat stimuli. Pain intensity was rated by participants using a visual analog scale. Salivary cortisol was assessed prior to 10 blocks of repeated painful heat stimuli, and 45 and 60 minutes afterwards.

RESULTS: In repeated measures analyses of covariance adjusting for age, sex, and time of examination, we found a significant effect of group (P < 0.01) and post-hoc tests confirmed that patients with chronic pain had lower cortisol area-under-the-curve values compared with healthy controls and depressed patients at all time points (all P values <0.01). However, cortisol secretion in depressed patients did not differ from controls.

CONCLUSIONS: Across groups, experimental heat pain stimuli did not elicit a significant cortisol response. Chronic pain appears to be associated with low cortisol secretion. The mechanisms linking chronic pain with low cortisol deserve further study.