Clinical characteristics and mechanism of pain in depression

Although there is a large amount of data indicating that depression and pain symptoms are closely interrelated, they are not included in depression symptoms in the classification systems. Even so, new developments in neuroscience have carried the data on this interrelation and co-occurrence beyond the epidemiological dimension to the awareness of a common underlying mechanism (1,2).

Although such a co-occurrence and the mechanisms that inşuence it are being discussed more and more, pain symptoms still cannot be well assessed or monitored and they are usually described by terms such as 'medically unexplainable', 'functional' or 'psychosomatic'.

The following statements may be made about the clinical characteristics of the symptoms (1):

• They do not conform to the anatomic localizations which would help explain their causes.
• They may vary in severity and location.
• Pain symptoms occur in 1/5 – 1/3 of patients with depression. These ratios are approximately 4 times higher than the ratios of those with no depression. The ratios in the literature about pain symptoms in patients with depression are approximately 65% on average (3).
• Chronic pain is a significant individual risk factor for suicide and self-injury.
• Chronic pain results in increases in treatment costs and a poorer outcome.
• The presence of pain as a residual symptom is the strongest predictor of recurrence.

It should be kept in mind that chronic pain, which is considered as being 'functional' in terms of the mechanisms involved in having pain during depression, is medically unexpected, self-generated and associated with vulnerability to pain. Therefore, central factors should play a leading role in experiencing it (4). Living with pain causes negative emotions, but beyond that, continuous pain is a physical symptom of depression. A neurobiological explanation of experiencing these two situations concurrently is not all that difficult when the broadness and diversity of the mechanisms involved in experiencing depression are taken into consideration (5).

The mechanisms involved in this co-occurrence may be summarized as follows:
• The connection between the emotional and somatic (e.g. pain) symptoms of depression is probably set up through the HPA axis. This system plays an important function in vulnerability to stress.
• The changes that emerge in the transfer of NA and 5HT in the CNS are of critical significance in terms of both depression and chronic pain pathophysiology (6). Monoamines regulate both mood symptoms and sensations of pain.
• Pain stimuli are carried from the periphery to the CNS by primary afferent fibers and are regulated by stimulating glutamate and suppressor GABA.
• The sub-cortical areas involved are the hypothalamus, periaqueductal gray matter, raphe dorsalis and locus coeruleus. These areas are also regulated by 5HT and NA.
• Cortical processing of a pain sensation is carried out in the relevant areas of the cortex.
In conclusion, it is obvious that common pathophysiological processes underlie the co-occurrence of depression and somatic pain symptoms seen in this picture and it is important to take such pain symptoms into consideration in a comprehensive treatment approach.

References:

1. Peveler R, Katona C, Wessley S, Dowrick C: Painfull symptoms in depression: under-recognized and under treatment. British J Psychiatry 2006;188:202-203.
2. Von Knorring L, Ekselius L: Idiopatic pain and depression. Quality of Life Research 1994;3:557-568.
3. Bair MJ, Robinson RL, Katon W, Kroenke K: Depression and pain comorbidity. A literatüre rewiev. Arch Gen Psychiatry 2003;163:2433-2445.
4. Mohr P, Bitter I, Svestka J, Seifritz E, Karamustafalıoğlu O, Koponen H, Sartorius N: Management of depression in the presence of pain symptoms. Psychiatria Danubina 2010;22:4-13.
5. Nemeroff CB, Vale WW: The neurobiology of depression: inroads to treatment and new drug discovery. J Clin Psychiatry 2005;66 (suppl. 7):5-13.
6. Wise TN, Fishbain DA, Holder-Perkins V: Painfull physical symptoms in depression: a clinical challenge. Pain Med 2007;8 (suppl. 2):75-82.