Pain and depression: the egg and the chicken story revisited.

The prevalence of pain in depressed individuals and the prevalence of depression in patients with pain are higher than when these conditions are considered individually. When pain is severe, impairs function, and/or is refractory to treatment, it is associated with more depressive symptoms and worse depression outcomes. Similarly, depression in patients with pain is associated with more complaints and greater functional impairment. Whether alleviation of pain helps depressive symptoms or, likewise, whether relief of depression improves pain, are questions still incompletely clarified. However, there is growing evidence that depression and pain share genetic factors, biological pathways and neurotransmitters. Thus, the most promising area of future research is elucidating the neurobiological alterations in pain pathways that intersect with those involved in depression.