Chapter 51: Chronic Pain Management

GENERAL CONSIDERATIONS

Pain is defined by the International Association for the Study of Pain as “an unpleasant sensory or emotional experience associated with actual or potential tissue damage or described in terms of such damage.” This emphasizes that the pain experience is multidimensional and may include sensory, cognitive, and emotional components. Additionally, it allows for the possibility, as in chronic pain states, that overt tissue damage may no longer be present. Chronic pain is pain persisting for >3 months or beyond the time of normal tissue healing. Many of the secondary problems associated with chronic pain, such as deconditioning, depression, sleep disturbance, and disability, begin within the first few months of the onset of symptoms of pain. Early identification and treatment are essential to reduce chronicity and prevent further disability.

Chronic pain is one of the most common complaints in primary care. The subjective nature of pain makes quantifying the incidence and prevalence a challenging endeavor. A 2012 population study estimated that 11.2% of adults, or 25.3 million adults, experience chronic pain, whereas the Institute of Medicine noted that 100 million Americans experience chronic pain with estimated annual medical and indirect costs of approximately $600 billion. Low back pain is most common, followed closely by migraines, neck pain, and other arthritic joint pain complaints. Given the frequency of chronic pain in primary care and its multidimensional nature, family physicians are uniquely positioned to support patients in preventing, treating, and coping with chronic pain.

PATHOGENESIS

The development of chronic pain is a complex interplay of modifiable and nonmodifiable risk factors unique to an individual. Studies performed on persistent postsurgical pain, persistent posttrauma pain, and postherpetic neuralgia assist in the understanding of the pathogenesis of chronic pain because of a defined mechanism and onset to the pain syndrome. Modifiable risk factors include such things as the nature and severity of the pain, predisposing mental health diagnoses, tobacco or alcohol exposure, physical activity and exercise, employment status, and occupational factors. Nonmodifiable risk factors include age, gender, cultural background, socioeconomic factors, epigenetics, and history of trauma, injury, or interpersonal violence.

The transition from acute to chronic pain involves a nociceptive and behavioral cascade with onset soon after the initial tissue injury. The noxious stimuli cause inflammatory changes leading to peripheral sensitization, which is known as acute pain. This stimulus is then transmitted via the spinal cord to the brainstem and cortical regions of the brain via afferent pathways. As this stimulus is processed, the individual characteristics of the patient will cause unique perception ...