Patients with chronic pain are known to be at high risk of developing depression.
The association between pain and depression is well recognised, and pain clinics routinely assess depressive symptoms. Their management plans often address depression as well as pain.
However, the same cannot be said for pain in patients with depression.
Such symptoms are likely to be under-recognised and inadequately or inappropriately managed in primary care and specialist psychiatric settings.
The problem might reflect inconsistent terminology and definitions, in particular the complex relationships between mind and body that is involved in the experience of pain and mood.
Much research in the area takes a simplistic approach that ignores the possible effects of pain on mood, behaviour and sleep, or the influence of depression on the subjective experience of pain.
Trials of antidepressants usually recruit patients free of physical illness or significant pain, and similarly depression is excluded in trials of analgesics.
The concept of 'somatisation' is particularly problematic. Studies attempting to classify depressed patients according to the extent to which they somatise have, not surprisingly, yielded inconsistent results.
The studies do, however, illustrate the rich variety of presentations across the emotional and physical spectrums.
Outcome studies in depression tend to focus on changes in core depression symptoms.
However, there has recently been a welcome recognition of the adverse prognostic significance of residual symptoms in patients, such as otherwise unexplained pain.
I have recently addressed these problems through a combination of literature review and expert consensus. The results have implications for clinical practice.
Patients with depression have an increased likelihood of painful symptoms, especially in low back pain.
Pain also appears to worsen response to treatment; this is particularly evident in the case of antidepressant drugs.
One recent study found that two thirds of patients in a trial of SSRIs experienced significant pain when first assessed.
The more severe the pain experienced, the higher the odds were for poor antidepressant response.
Another study found that those depressed patients who experienced painful symptoms that improved during antidepressant treatment were much more likely to experience a remission of their depressive state.
Coexistent pain and depression also carry a greater burden on healthcare services and time off work. This might reflect problems in diagnosis.
Depression and pain might share common pathways involving both serotonin and noradrenaline.
Depression and unexplained pain might both be associated with adverse childhood experiences and with a characteristic resultant pattern of behaviour involving 'catastrophising'.
This can be explained as overestimating the severity of internal or external threats and the excessive avoidance of these threats.
There is also limited evidence suggesting that antidepressants that have effects on both noradrenaline and serotonin might be more effective in the treatment of painful symptoms than antidepressants that have effects on the serotonergic system alone.
Both GPs and psychiatrists should be alert to the importance of pain symptoms in patients with depression.
Teamwork and respect for patients' own models of illness and treatment are essential in improving outcomes.
- Professor Katona is Dean at the Kent Institute of Medicine and Health Sciences at the University of Kent, Canterbury, Kent
TREATING PAIN AND DEPRESSION
A combination of literature reviews and expert consensus leads to a number of recommendations:
1. Katona C, Peveler R, Dowrick C et al. Pain symptoms in depression: definition and clinical significance. Clinical Medicine 2005; 5 (4): 390-5.
2. Bair M J, Robinson R L et al Impact of pain on depression treatment response in primary care Psychoso Med 2004; 66: 17-22
3. Fava M, Mallinckrodt C H et al. The effect of duloxetine on painful physical symptoms in depressed patients. Clin Psychiatry 2004; 65: 521-30.