It has been well established that there are high levels of comorbidity between chronic pain conditions and mental health disorders. Moreover, psychiatric conditions, such as depression, anxiety, substance abuse, personality disorders, and post-traumatic stress disorder (PTSD), occur more frequently in patients with chronic pain than in the general population.
Many clinical researchers have proposed explanations for the co-occurrence of pain conditions and mental health disorders. The strongest evidence has been found in support of biopsychosocial models, which simultaneously incorporate both biological and psychosocial components. This article will address the biological process involved in mental illness and pain
Many of the same neurotransmitters are implicated in both pain and psychosocial disorders, including serotonin, norepinephrine, and dopamine.
Low levels of serotonin have been associated with migraine, cluster, and analgesic abuse headaches, as well as fibromyalgia
Antidepressants that inhibit serotonin reuptake have been shown to improve symptoms in temporomandibular disorders (TMD), tension-type headaches, FM, and certain neuropathic pain conditions
The investigators hypothesized that dysfunction of the serotonin system may be responsible for the failure to modulate sensory inputs, leading to greater vulnerability to chronic pain conditions. Numerous other clinical trials have also been conducted that revealed a correlation between decreased serotonin functioning and lowered pain thresholds
The relationship of the neuroendocrine system, especially the hypothalamic–pituitary–adrenal (HPA) axis, to both psychosocial and pain disorders has been well established. The HPA axis is the body’s primary stress pathway, and it is activated by corticotropin-releasing factors from the hypothalamus, which stimulate the release of cortisol from the adrenal glands. Cortisol modulates the metabolism of serotonin, norepinephrine, and dopamine
The dysregulation of cortisol has been associated with a number of pain conditions, such as TMD, FM, and chronic daily headaches. Additionally, mental health disorders, such as anxiety, depression, PTSD, and substance abuse, are associated with abnormal HPA axis functioning. Several clinical studies have concluded that evidence of cortisol dysfunction is particularly strong in patients with comorbid pain conditions and major depressive disorders (MDD)
fMRI Brain Imaging
several brain areas have been identified as important in the processing of both pain and mood state.
Reduced cerebral blood flow to the thalamus, a region of the brain responsible for relaying signals to the cortex, has been found in both chronic pain and depression
Similarly, the dorsal anterior cingulate cortex, anterior insula, and amygdala are involved in both depression and the emotional appraisal of painful sensations.
Giesecke et al found that the presence of MDD and chronic pain was associated with activation of the amygdala and anterior insula (brain areas that process the emotional and motivational aspects of pain) in response to experimental pain
Numerous researchers have proposed that both chronic pain and MDD involve abnormal anticipatory processing and hypervigilance.
Peripheral Pain-Processing Mechanisms
Differences in peripheral pain processing have been documented in patients with comorbid pain and mental health disorders.
Klauenberg et al found that patients with both chronic pain and MDD failed to inhibit pain under conditions of repetitive stimulation, with repetitive noxious stimuli leading to a decompensation of the patients’ pain suppression mechanisms.23
Giesecke et al proposed that the association of sadness with pain was common to both chronic pain and depression, as was learned helplessness, a condition in which a person who has been unable to control a noxious stimulus eventually stops trying and responds with depressive symptomatology.
When there’s no relief from chronic pain, a person has no recourse but to submit to it.
Cognitive mechanisms also have shown an association with both pain and psychosocial conditions
Catastrophizing, which refers to responding to negative events with overwhelming helplessness and by seriously overestimating the likely negative consequences, is associated with pain, depression, and anxiety. Several researchers have found support for the hypothesis that catastrophizing and other negative appraisals of pain alter the effects of depression on the affective and evaluative experience of pain
Yet permanent chronic pain is a catastrophe almost by definition.
Personality traits also have been linked to both pain and mental health disorders.
Neuroticism, a tendency to experience negative emotional states, has been associated with psychosocial disorders, including PTSD, anxiety, and depression, as well as pain conditions such as TMD, low back pain (LBP), and migraine headache
Another personality trait linked to chronic pain and psychosocial disorders is anxiety sensitivity, which increases risk for panic and anxiety disorders and is associated with chronic musculoskeletal pain and recurrent headache
Other psychosocial factors that influence chronic pain and psychopathology include self-regulation and coping strategies. Self-regulation often is lacking in personality disorders.
in some patients with borderline personality disorders, chronic pain is related to a failure to regulate the experience of pain and the emotional reactions associated with pain
Coping strategies that are passive (such as hoping) or avoidant (such as reducing activity or isolation) also are associated with comorbid chronic pain and depression.
This model emphasizes the interactions among biological, mental health, and social factors in the development and maintenance of chronic pain and mental health disorders
Transition From Acute to Chronic Pain
Gatchel described the role of biopsychosocial processes in the transition from acute to chronic pain (Figure).
In stage 1 (acute pain), the physical painful stimulus evokes emotional reactions of fear, anxiety, and worry. These reactions are adaptive in prompting the organism to avoid physical harm and seek treatment for injuries; however, if pain symptoms persist beyond the normal healing period of 2 to 4 months, the patients progress into stage 2 (subacute pain).
In this stage, greater variations in emotional reactions are seen. The stress of unrelieved pain will tend to exacerbate preexisting personality characteristics and psychosocial characteristics. The emotional reactions of stage 2 also are affected by social and economic conditions. Patients who receive secondary gains from pain conditions, such as financial compensation or sympathy, may be more likely to experience symptom magnification and somatization. If pain symptoms are not resolved by the fourth month, the patient progresses into stage 3 (deconditioning).
In this stage, the person becomes habituated to the sick role and accustomed to exemption from normal social and occupational responsibilities and obligations, which may trigger depressive symptoms and maladaptive coping strategies that can progress into diagnosable conditions such as MDD or personality disorders.
The entire process of transition from acute to chronic pain also is affected by physical factors. If the person responds to pain sensations with activity avoidance or abnormal movement patterns, physical deconditioning may develop
However, it should be noted that this model does not claim that psychosocial factors cause chronic pain. Instead, the form of mental health disorders that co-occur with chronic pain depends on preexisting personality traits and psychosocial characteristics
The Diathesis–Stress Model
psychopathology develops from an interaction of genetic predisposition and environmental triggers. This model has been adapted to explain the comorbidity of pain and psychosocial disorders
In contrast, researchers also have claimed that chronic pain is the stressor that activates preexisting depressive tendencies. The stress may result from the physical sensation of pain, as well as the secondary losses (financial, physical ability, self-esteem, etc.) associated with pain
The Biopsychosocial Model
The biopsychosocial model of chronic pain is a comprehensive perspective that encompasses all the aspects of the pain experience. It has four primary components: biological, physical functioning, mental health, and social function.
Pain is most complex when it persists over time, with mental health, social, and economic factors interacting with physical pathology to modulate the experience of pain and the development of subsequent disability. The effectiveness of biopsychosocial treatment programs has been well established for the treatment of chronic pain and for psychiatric disorders
Temporal Relationships Between Chronic Pain and Psychosocial Disorders
Studies on the temporal relationship between the onset of pain and the onset of diagnosable psychopathology have revealed that certain psychiatric disorders precede chronic pain (substance abuse, anxiety disorder), whereas others (MDD) develop either before or after the onset of pain
The prevalence of most Axis I disorders were also found to be elevated only after onset of injuries.
Although mental health disorders are frequently comorbid with chronic pain conditions, the combination of pain and psychopathology does not necessarily translate to poor response to treatment, particularly if a biopsychosocial treatment model is used
The past decade has produced an abundance of scientific literature supporting a major paradigm shift from the outdated biomedical model to the much more integrative biopsychosocial one to address this problem.
First published on: September 30, 2011