Pain: Treatments for Chronic

Underlying Causes of Chronic Pain

Although chronic pain may be the result of misdi-agnosed, mismanaged, or persistent acute pain, many believe that the development and maintenance of chronic pain is a complex process that involves the interplay between psychosocial and physical factors. According to this biopsychosocial model of pain, pain is conceptualized as a multidimensional phenomenon that is influenced by many factors, including mood, previous experience, and cultural and other beliefs about pain, in addition to sensory input. It is also recognized that people with pain demonstrate widely different emotional and behavioral responses to similar levels of pain intensity. Thus, how a person copes with or responds to acute pain is an important determinant of the development of chronic pain.

In the transition from acute to chronic pain, the source of nociceptive input may change from the periphery to the central nervous system. This phenomenon, referred to as central sensitization, is thought to occur in response to repeated stimulation from peripheral pain fibers. Constant signaling over time is believed to sensitize pain neurons in the spinal-thalamic tract, leading to enhanced responses to peripheral nociceptive input and spontaneous [Page 730]firing. Thus, pain signals to the brain may be amplified or produced in the spinal cord, even when peripheral pain input is diminished or absent. In addition, premorbid physical factors may also influence the development of chronic pain. There is emerging evidence that genetics play a role in human pain perception. For example, genes that influence catechol-O-methyl transferase (COMT), an enzyme that breaks down catecholamines, GTP cyclohydro-lase, a building block in other amino acids, and Nav1.9, a sodium channel that is preferentially expressed in nociceptive neurons in the dorsal root ganglia, have all been found to be associated with human pain sensitivity. In addition, prospective studies have found that genes associated with COMT predict the development of chronic pain conditions such as temporomandibular joint disorder and knee osteoarthritis. These genetic factors may augment the intensity of any acute pain problem, increasing the likelihood of developing chronic pain.

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