Does chronic pain cause the depression or does depression cause the
pain? Current evidence supports both relationships.[34-39]
Research shows that patients with persistent or chronic pain are at risk
for developing an anxiety or depressive disorder.[40-42] A
recent analysis[34] of data from the World Health
Organization, found that 22% of primary care patients complained of
persistent pain, which was defined as experiencing at least 6 months of
pain plus disability because of the pain and/or receipt of medical care
for the pain. Those with persistent pain were 4 times more likely to
have an anxiety or depressive disorder than were pain-free individuals.
A host of other psychological and social factors may also be involved
in the development of chronic pain.[34,37] Gureje and
colleagues[34] analyzed data from the World Health
Organization to examine persistent pain in more than 3000 primary care
patients around the world. Researchers found that 49% of patients who
experienced persistent pain at baseline continued to have persistent
pain 12 months later. The best independent predictor of persistent pain
was the number of pain sites. Psychiatric disorder, poor self-rated
overall health, and occupational related disability were also found to
be independently associated with chronic pain. Furthermore, persistent
pain at baseline predicted the onset of a psychological disorder with
the same strength that a baseline psychological disorder predicted the
onset of persistent pain.
In their review of the epidemiology of pain and depression in primary
care, Von Korff and Simon[43] made 4 broad generalizations.
They are as follows:
- Pain is as strongly associated with anxiety as with depressive
disorders;
- The number of pain sites (diffuseness of pain) and the extent to
which pain interferes in daily life are the characteristics that
most strongly predict depression;
- Certain psychological symptoms of depression, including low
energy, sleep disturbances, and worry, are common among pain
patients whereas guilt and loneliness are not; and
- Psychological distress and disability often surface and resolve
early during the course of a pain disorder that evolves into a
chronic condition.
Based upon their findings, these researchers hypothesized that pain
and psychological illness have reciprocal psychological and behavioral
effects. They proposed 2 theories about the mechanisms underlying the
pain-depression comorbidity: (1) some individuals are genetically
susceptible to both physical and psychological symptoms and a state in
which psychological distress amplifies unpleasant physical sensations;
(2) the physical and psychological stress of pain may induce or
aggravate psychological distress.
Other, more recent models of the relationship between pain and mood
blend the evidence from studies of neurobiological and biobehavioral
concepts such as sensitization, conditioning, and kindling to explain
the comorbidity of pain and depression.[44]
