BASICS

• Chronic pain is pain persisting beyond the time of normal tissue healing, usually >3 months.
• Over time, neuroplastic changes in the CNS transform pain into a chronic disease itself. Pain levels can exceed observed pathology on exam or imaging.
• Pain experience is inherently related to emotional, psychological, and cognitive factors.
• An epidemic of undertreated pain coexists with an epidemic of prescription drug abuse in the United States.
• Use a system-based practice to safely and effectively prescribe opioids when indicated for chronic nonmalignant pain.

EPIDEMIOLOGY

Incidence
Incidence is rising, but exact rate is unclear. The annual economic cost of chronic pain in the United States is estimated at $560 to $635 billion (1)[B].

Prevalence
In the United States, an estimated 100 million adults live with chronic pain—more than the total affected by heart disease, cancer, and diabetes combined (1)[B].
Chronic pain accounts for 20% of outpatient visits and 12% of all prescriptions (2)[B].

ETIOLOGY AND PATHOPHYSIOLOGY

• With intense, repeated, or prolonged stimulation of damaged or inflamed tissues, the threshold for activating primary afferent pain fibers is lowered, the frequency of firing is higher, and there is increased response to noxious and/or normal stimuli (peripheral and central sensitization). The amygdala, prefrontal cortex, and cortex are thought to relay emotions and thoughts that create the pain experience, and these areas may undergo structural and functional changes with chronic pain.
• Many patients have an identifiable etiology (most commonly musculoskeletal problems or headache), but pain levels can be worse than observable tissue injury. A significant percentage of patients have no obvious cause of chronic pain.

Genetics
Current research suggests genetic polymorphism in opioid receptors, which may affect patient’s response and/or side effects to individual opioids.

RISK FACTORS

• Traumatic: motor vehicle accidents, repetitive motion injuries, sports injuries, work-related injuries, and falls
• Postsurgical: any surgery but especially back surgeries, amputations, and thoracotomies
• Medical conditions: See “Commonly Associated Conditions” later.
• Psychiatric comorbidities: substance abuse, depression, posttraumatic stress disorder (PTSD), personality disorders
• Aging: increased incidence with age but should not be considered a “normal” part of aging

GENERAL PREVENTION

• Avoidance of work-related injuries through the use of ergonomically correct workplace design
• Exercise and physical therapy to help prevent work-related low back pain
• Varicella vaccine and rapid treatment of shingles to lower risk of postherpetic neuralgia
• Tight glycemic control for diabetic patients, alcohol cessation for alcoholics, smoking cessation

COMMONLY ASSOCIATED CONDITIONS
Any chronic disease and/or its treatment can cause chronic pain, including diabetes, cardiovascular disease, HIV, progressive neurologic conditions, lung disease, cirrhosis, autoimmune disease, cancer, renal failure, depression, and mental illness.