Definition and Epidemiology

Chronic pain is a complex, subjective, persistent, unpleasant sensory and emotional experience that affects more than 100 million people in the United States and has associated health care costs of up to $635 billion. Pain is a normal physiologic response to an actual or potential injury that prompts a useful protective response, but chronic pain may occur in the absence of injury, has no known physical benefit, and carries significant morbidity and mortality.¹ Chronic pain is defined by the International Association for the Study of Pain as “pain that persists beyond the expected time frame for healing.” Any pain can be considered chronic if it continues 90 days past a reasonable healing time.² Chronic pain is self-perpetuating and influenced by factors that are both pathogenetically and physically remote from the originating cause.³ Because complete pain relief is unlikely, control strategies for chronic pain extend from encouragement of local reparative processes to a more global management strategy of rehabilitation. Therapy focuses on promoting optimum functioning, coping, and quality of life with use of a full-dimensional approach of interdisciplinary care and community supports in decision-making and goals.⁴

Multiple conditions may result in the development of chronic pain, including headaches, low back pain, abdominal or pelvic pain, noncardiac chest pain, regional pain syndromes, and neuropathies and conditions that are vascular, cutaneous, musculoskeletal, cancerous, or psychological in nature.⁴ The pain may be part of a broader clinical situation, such as a work-related injury, accident, trauma, or comorbid disease states. Patients with chronic pain typically seek a health care provider initially for headache, abdominal pain, musculoskeletal discomfort, or neurologic pain relief. Pain can also be related to other organic disorders, including diabetes, end-stage renal disease, alcoholism, and postherpetic syndromes.⁵ There is also chronic pain syndrome. Both chronic pain and chronic pain syndrome can exist in the same patient, but the syndrome is complicated by physical, psychological, emotional, and social aspects.² Concomitant and well-known psychological sequelae to chronic pain include significant depression, anxiety, and anger. In 2010 the concept of mental defeat was introduced into the chronic pain literature. A psychological construct derived from work regarding torture and depression, it is described as an aspect of catastrophizing strongly associated with functional and psychosocial disability, emotional distress, self-reported pain interference, and sleep disturbance in patients with chronic pain. Treatment strategies aimed at prevention or reversal of mental defeat offer ways to reduce pain-related disability and to increase functionality.⁶ Further studies on mental defeat in the Hong Kong chronic pain population found significant distress and disability among those seeking treatment for their pain, and it is thought that early identification of mental defeat can help with early intervention for depression and anxiety.⁷

This chronic pain state with its concomitant mood disorders results in negative alterations in daily activities, function, and personality.⁵ Both chronic pain and its management can adversely influence respiration, mobility, and functional and mental status, with resulting disturbed sleep patterns, pneumonia, constipation, and venous thromboembolism. The adverse effects of chronic pain can be particularly deleterious in the elderly.⁷

Pathophysiology

Pain is an unpleasant sensation unique to each patient. According to McCaffrey, “pain is whatever the experiencing person says it is, existing whenever the experiencing person says it does.”⁸ Chronic pain is caused by a “chronic pathologic process in somatic structures or viscera, or by prolonged and sometimes permanent dysfunction of the peripheral and central nervous system or both.”³ The physiologic, affective, and behavioral responses to chronic pain are quite different from the responses to acute pain. Pain is categorized pathophysiologically as either organic or idiopathic, and organic pain is further delineated as nociceptive (somatic or visceral) or neuropathic.

Somatic pain is caused by the activation of nociceptors in the peripheral tissues, including skin, bones, muscles, and soft tissue. It is usually described as being well localized and characterized as stabbing, aching, or throbbing. In contrast, visceral pain is usually poorly localized and often is not attributable to the involved organ (i.e., referred pain). It may be described as dull, crampy, or deep. Visceral nociceptive pain can be referred in a dermatomal distribution, because often the autonomic fibers innervate the organs or hollow viscera found in the dermatome.⁹

Organic neuropathic pain occurs as a result of injury or disease of the nervous system. Because it follows the distribution of peripheral nerves in a dermatomal pattern, neuropathic pain is most often described as burning, shooting, or tingling. Central neuropathic pain is caused by damage of the nerves in the central nervous system (CNS).⁹ Idiopathic pain may not demonstrate any clinical evidence of an associated organic cause but might include additional psychological elements at the time of presentation. Nonetheless, as previously stated, the experience of pain is purely subjective. Subsequently, the reality of a patient’s idiopathic pain is comparable to that of organic pain, and therefore it must be treated.

Clinical Presentation

The clinical picture of chronic pain may be nonspecific and noted only in terms of a retrospective review, in which certain patterns may emerge. Both physical and psychological elements must be considered in a patient with chronic pain. As established, chronic pain is pain that continues for a prolonged period and beyond a reasonable healing time for a specific injury. The majority of patients with chronic pain in a recent study were being managed by their primary care physician, and few have ever seen a pain specialist.¹⁰ Almost half of this study population had undergone radiographic tests in the prior 6 months, over three quarters were taking prescription medication for their pain, and half were using nonpharmacologic modalities in an attempt to manage pain.¹⁰

Patients who visit clinics with chronic pain often have additional issues such as depression, anxiety, sleep issues, overuse of medications, relationship issues, isolation, and low level of physical activity.^11,12 Adequate treatment may be complicated by a history of difficult patient-provider interactions in the past, financial barriers, and general lack of support. Despite the high prevalence of chronic pain, the varying results of studies in interdisciplinary approaches make it difficult to establish how to best treat these patients.

Physical Examination

Pain is frequently undermanaged because of poor clinical assessment. It is critical that pain assessment be integrated into a detailed history and physical assessment, with reassessment at each visit. An initial comprehensive clinical pain history should include past relevant health issues, psychiatric history, psychosocial factors, addiction risk, social and occupational functional assessment, goals of treatment, and pain beliefs. Previous treatments and outcomes, both traditional and alternative therapies, should be explored. A thorough review of current medications, including over-the-counter and complementary medications, should be included.¹³ A referral to a behavioral specialist may be helpful.¹⁴

Pain assessment can be aided by the mnemonic PQRST.¹⁵ P stands for provocative-palliative factors, such as specific positions or movement, temperature, or activities. Q stands for quality and includes the description of the pain, such as dull, boring, aching, or electrical. R stands for the region or site of pain, such as the torso, abdomen, back, or spine. S stands for severity and refers to how severe the pain is, measured by rating the pain over time. Most commonly, to quantify their pain, patients are asked to use a scale of 1 to 10, a scale of calm to distressed faces, or a scale of description of no pain to worst pain. No one scale applies to all patients; rather, the important issue is to choose one scale that is appropriate for a patient and use it consistently. T is for temporal or the timing of the pain during day or night, in which the pain is more constant or the duration longer. Box 222-1 offers sample questions for assessment.

The physical examination of a chronic pain patient should be thorough and multifactorial. It should include a general examination of appearance, gait, neurologic and mental status, cranial nerve testing results, motor and musculoskeletal strength, and reflexes and a full joint and myofascial examination.¹⁶