Relationship Chronic Pain and Chronic Stress

  • A review of the commonalities and differences between chronic pain and stress with emphasis on the neurobiological processes with the limbic system as the central mediator, and whether chronic pain can be considered under the larger umbrella of chronic stress
  • First of two mutually non-exclusive models linking pain and stress considers pain as one type of stress that leads to allostatic overload to the body and brain with dysregulation (over-activity or inactivity) of multiple physiological systems that are involved in adaptation to environmental challenge. The result is compromised well-being and social dysfunction
  • The second model examines unpredictable and multiple life stressors precipitating chronic pain, leading to a vicious cycle of maladaptive physiological responses leading to increased vulnerability and persistence of pain.
  • Acute stress activates the HPA axis (hypothalamus-pituitary-adrenal) leading to the release of glucocorticoids. These hormones have receptors in the hippocampus, amygdala, and prefrontal cortex (PFC).
  • Acute stress also activates the autonomic nervous system, updating emotional states with the ultimate effect on behavior, ie fight or flight.
  • Although acute pain can be conceptualized as a form of acute stress, the details of the neural and endocrine responses can be different. For example, evidence that acute pain activates the HPA axis is unclear. However, at the brain level, fMRI studies of the brain in response to stress demonstrate noticeable overlap in the amygdala, hippocampus, and anterior cingulate cortex.
  • Stress and pain both engage learning centers of the hippocampus, amygdala, and PFC. Fear conditioning and extinction (Pavlovian) are involved and both PTSD and chronic pain can be considered conditions in which brain fails to extinguish the negative memory.
  • The neurochemical properties of the learning circuitry and its adaptive response to chronic stress or pain are believed to be crucial in determining remission or persistence of pain and stress response beyond what is considered evolutionarily advantageous.