The role of stress and depression in pain
The association among physical and psychosocial stressors, depression, and chronic pain syndromes has been the subject of numerous studies.
Posttraumatic stress disorder (PTSD) has been closely correlated with chronic pain. An example of one such stressor may be deployment to a military conflict. Soldiers and military personnel throughout history have reported a cluster of symptoms such as pain, fatigue, and cognitive impairment that are very similar to FM. From US military conflicts, these syndromes include Gulf War illness, the condition known as “shell shock” in World War I, and “soldier’s heart” during the Civil War.
A review of the literature addressing the association between chronic pain and PTSD by the Department of Veterans Affairs found such a high degree of correlation that the authors suggested clinicians who conduct diagnostic assessments for one disorder should also assess for the other.22 In a study that evaluated patients for FM, chronic fatigue, and psychiatric symptoms, patients with FM who had both tender points and diffuse pain were significantly more likely to have an increased prevalence of lifetime PTSD.23
The relationship between depression and chronic pain has been well documented. Kaiser Permanente surveyed patients seen in primary care and found that a significantly higher proportion of patients with major depressive disorder (MDD) reported chronic pain than did patients without MDD (66% vs 43%, respectively).24 These conditions share common physiologic features and a high degree of comorbidity.
A study of patients with FM and depressive symptoms or MDD looked at neural responses to painful pressure and found no association between the extent of depressive symptoms or MDD and neural activation in the primary and secondary cortices, areas associated with the sensation of pain. However, activation was seen in the amygdala and contralateral anterior insula, areas associated with affective pain processing.25
These findings were supported in a more recent study in which patients who met the criteria for FM were given a series of questionnaires to assess depressive symptoms, anxiety, and catastrophizing, and were tested for painful pressure responses using fMRI. The results established a correlation between this cluster of affective symptoms, but there was no correlation with clinical pain symptoms or responses to painful pressure.26 Rather than suggesting that there is no alignment between the mental and physical aspects of pain, results from both of these studies suggest that 2 independent pain networks exist to process the sensory and affective dimensions of pain, and that these pathways may operate simultaneously.
Pain in the clinical setting
The evidence is strong that many patients experience chronic pain that is not site-specific and arises not merely from the periphery but from intricate neural systems. With a new appreciation for the complexity of pain processing, the clinician is compelled to probe beyond, “Where does it hurt?” [Table].
TABLE: Clinical diagnosis of central pain
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When patients complain of widespread or chronic pain, the clinician is well advised to take the time to examine further by inquiring about depression, anxiety, fatigue, sleep disturbances, and cognitive difficulties in order to understand what is driving the patient’s symptoms.13 The results may be revealing. In a study of primary care patients, participants who complained of muscle pain, headache, and stomach pain were found to be 2.5 to 10 times more likely to screen positively for panic disorder, generalized anxiety, or MDD.27
An article in a following issue will discuss practical tools that can be used to assess comorbidities such as anxiety and depression, and interventions that might be helpful for central pain and neurorehabilitation. An approach that acknowledges the patient’s account of pain, recognizes the cluster of symptoms and conditions that can accompany pain, and utilizes a multidisciplinary approach for diagnosis and treatment will have the best chance of yielding positive outcomes.
Acknowledgement—The author wishes to thank Kristen Georgi for her assistance in the research and writing of this article.
REFERENCES
1. International Association for the Study of Pain. IASP taxonomy: pain terms. Pain. Available at: http://www.iasp-pain.org/AM/Template.cfm?Section=Pain_Defi...isplay.cfm&ContentID=1728#Pain.
2. Melzack R, Wall PD. Pain mechanisms. A new theory. Science. 1965;150:971-979.
3. Carr DB. How prevalent is chronic pain? Pain Clinical Updates. 2003;11:1-4. Available at: http://www.iasp-pain.org/AM/AMTemplate.cfm?Section=Home&CONTENTID=7594&TEMPLATE=/CM/ContentDisplay.cfm&SECTION=Home.
4. Washington, DC: US Department of Health and Human Services, Centers for Disease Control and Prevention; 2006. Bernstein AB, Makuc DM, Bilheimer LT. Health, United States, 2006. Available at: http: //www.cdc.gov/nchs/data/hus/hus06.pdf.