Pain: Psychological Correlates 2

By Dr.Thilini Rajapakse, Dr. Dilani Wijeratne

and Dr. Ranjith Pallegama

 

Chronic pain and depression

     There is an increased association between chronic pain disorders and psychiatric conditions. Depression is the most commonly studied psychiatric disorder in the context of chronic pain. Other than depression, anxiety disorders, somatoform disorders, substance use disorders and personality disorders have all been found to be more common among patients with chronic pain compared with those without chronic pain.

 

Nature of the link

     Interaction between chronic pain and depression has been labeled by some authors as the depression-pain syndrome or depression-pain dyad, implying that the condition often coexist, respond to similar treatments, exacerbate one another, and share biological pathways and neurotransmitters. Although it is generally understood that depression and painful symptoms are common comorbidities and that their combination is costlier and more disabling than either condition alone, their interaction is not fully understood.  The debate about whether depression, for example, is antecedent, consequent, or concomitant to chronic pain is largely unresolved. Several population based longitudinal studies have emerged supporting the hypothesis that mood disorders can increase the risk of developing chronic pain. However, it should be noted that chronic pain in turn can lead to long lasting emotional disturbances often referred to as ‘secondary pain effect’.

     In patients with physical conditions and pain, depression rates range from 13% to 85% and are higher than those seen in patients without pain. Conversely, similarly high rates of pain are observed in depressed patients in community-based medical settings. Generally, the estimated rates of comorbidity have been between 30% and 70%. The studies have shown that prevalence of major depression increased with greater pain severity.

     A telephone survey conducted of a random sample of 18 980 subjects in 5 countries found the prevalence of one chronic pain condition to be 17.1% and the prevalence of at least one depressive symptom was 16.5%. Chronic pain prevalence increased with number of depressive symptoms, and was 4 times more prevalent among those with major depression.

     Patients whose chronic pain conditions are comorbid with psychiatric disorders have poorer treatment outcomes and greater levels of disability than those without. Comorbidity of chronic pain with depression is associated with considerable medical and social morbidity, loss of productivity, and considerable direct and indirect financial costs. A German study of 4000subjects in the community found that pain and depression were associated with poorer general functioning. In a clinical sample of primary care patients in the Kaiser Managed care system in the United states, comorbid pain and major depression were associated with a significantly greater clinical burden.

             The presence of a chronic pain together with depression often leads to a vicious cycle, where the depression worsens the pain symptoms, and the pain symptoms further worsen the depression. 

 

Figure: Chronic pain syndrome and depression- a vicious cycle:

 

 

 

 

 

 

 

Mechanism of the link between pain and depression

     Several brain regions including insular cortex, prefrontal cortex, anterior cingulated cortex, amygdale and hippocampus have been implicated in both major depression and pain. Insular cortex is frequently activated in response to chronic pain. This area of brain is responsible for processing information from sensory experiences to create an emotionally relevant context. Imaging studies revealed focal changes of the serotonin 5HT2 receptor status in the insular cortex of depressed patients.

     Prefrontal cortex- the most prominent feature of the prefrontal cortex is its role in executive functions like working memory, planning, and judgment; impairments of all these functions are observed in patients with depression. Studies revealed changes in blood flow and activity in various areas of prefrontal cortex in patient with depression. Activation of the prefrontal cortex has been observed in clinical pain conditions and is associated with a role in attending to or ignoring painful stimulation.

     Anterior cingulated cortex- The anterior cingulated cortex plays an important role in conflict detection and emotional evaluation of error. In addition, it is connected to brain structures that influence the emotional valence of thought, autonomic and visceral responses, and mood regulation. All of these functions are disturbed during depression. Changes in activity of anterior cingulated cortex are also noted in patients experiencing pain.

     Amygdala- The amygdale performs a primary role in the formation and storage of memories associated with emotional events, processes which are disturbed in patients with depression. The amygdala plays a key role in attaching emotional significance to pain.

     Shared neurocircuitries and neurochemicals play an important role connecting the pathophysiology of depression and pain disorders. Hypothalamic-pituitary-adrenal axis, ascending and descending pain tracks, Limbic and paralimbic structures, monoamines, neurotrophic factors and cytokines all been implicated in pathophysiology of chronic pain and depression. These shared pathways enable cross talk between both disorders on several levels – within and between brain regions, intercellular and through neurochemical signaling. Therefore, alterations in the activity of neurocircuitries and the levels of neurochemicals due to either disorder can affect the other disorder.

 

Diagnosis

     Depressive symptoms in patients suffering from chronic pain can easily be missed as there is an overlap of some symptoms in these patients. As chronic pain can be a source of significant distress to patients, clinicians may not fully address depressed mood as part of a comorbid illness.

     Characteristic features of depression includes a depressed mood for most days for at least 2 weeks, loss of interest or pleasure, change in appetite, sleep, fatigue or loss of energy, impaired concentration, psychomotor agitation or retardation, feelings of worthlessness and excessive guilt and suicidal ideation.

     Chronic pain is associated with a threefold increase in risk for experiencing suicidal ideation and a two to eight fold increase in risk for committing suicide. One obvious factor in this increased risk for suicide is co-morbid depression. For example, in a U.S. community sample of young adults, Breslau noted an eightfold increase in risk for suicidal ideation in subjects with migraine with aura and co-existing major depression compared with subjects with migraine with aura alone and a 2.6 fold increase compared with subjects with major depression alone.

 

Treatment of depression in patients with chronic pain

     Convincing evidence exists showing that treating comorbid mental disorders improves self-reported pain as well as the functional outcomes of patients with chronic pain. It is important to address both comorbidities when treating depression in chronic pain patients.

 

Psychotherapy

     Cognitive behavioral therapy is the commonly practiced type of psychotherapy for depression and chronic pain. There is a lot of evidence for efficacy of cognitive behavioral therapy for pain and depression. It is more effective when used as part of a comprehensive treatment plan for patients with comorbid disorders.

 

Pharmacotherapy

     As described above, monoamines (serotonin and norepinephrine) are involved in the pathophysiologies of both depression and pain. Tricyclic antidepressants (TCA) and the newer serotonin and norepinephrine reuptake inhibitors (SNRIs) duloxetine, venlafaxine have shown efficacy in the treatment of both conditions, an effect that might be due partially to their facilitating influence on both serotonin and norepinephrine. Selective serotonin reuptake inhibitors (SSRIs) seem to be less efficient in the combined treatment of pain (particularly neuropathic pain) and depression.