Chronic pain can be defined as
unrelenting, intractable pain commonly caused by injury or disease, and
often occurs after healing is complete; chronic pain can also exist in
the absence of disease. According to pain researchers John Loeser and
Ronald Melzack, chronic pain is distinguished from acute pain in that
therapies for the former only provide transient relief and do not
resolve the underlying pathologic and healing processes: "Chronic
pain will continue when treatment stops."[1] The
American Pain Society has adopted the definition of chronic pain offered
in the Textbook of Pain (4th edition, 1999):[2]
"Generally considered to be
pain that lasts more than 6 months, is ongoing, is due to
non-life-threatening causes, has not responded to current available
treatment methods, and may continue for the remainder of the person's
life."
The intensity and persistence of
chronic pain may be influenced by physical, emotional, and social and
other environmental stresses. Of note, the intensity of chronic pain may
not be related to the extent of tissue injury or other quantifiable
pathology, and the persistence of pain may be due to factors other than
the initial tissue damage or insult that triggered the onset of pain.[1]
Chronic pain of moderate to severe
intensity is typically associated with advanced stages of cancer and may
be due to tumor invasiveness or metastasis, or to current or prior
chemotherapy or radiotherapy.[3] Moderate to severe chronic
pain is also encountered outside of the cancer setting, and may be
associated with noncancer disorders such as arthritis, sickle cell
anemia, low back pain, headaches, neuralgia, and fibromyalgia.[1,4,5]
Frequently, patients with chronic cancer or noncancer pain experience
relatively short episodes of worsening pain, which are referred to as
breakthrough or episodic pain.[6,7] Thus, chronic pain can be
thought of as consisting of two components: a relatively constant
component (baseline pain) and an intermittent component superimposed on
the baseline pain (breakthrough pain).
Regardless of its cause, chronic pain
negatively impacts quality of life, often profoundly affecting mobility,
mood, personality, and social relationships. Patients typically
experience concomitant decreased overall physical and mental
functioning, depression, sleep disturbance, and fatigue.[4,8,9]
Because of the multidimensional impact of chronic pain (ie, severely
reduced physical, psychological, and social well-being), pain is only
one of many issues that must be addressed in the management of patients
with chronic pain. Optimal pain management of patients with chronic pain
frequently requires both pharmacologic and nonpharmacologic
interventions. Nevertheless, pharmacologic therapy remains the
foundation of cancer pain management. Effective pain management is best
achieved by a team approach involving patients, their families, and
healthcare providers.[10] It is important to note that this
activity is not a comprehensive review of all chronic pain management
strategies; rather, this article considers only the pharmacologic
management of moderate to severe chronic pain, including breakthrough
pain, in cancer and other patient populations.
The use of opioid analgesics for the
treatment of chronic pain represents a key component of a comprehensive
care program. Indeed, long-acting opioids have been shown to improve the
quality of life in patients with chronic pain of both cancer and
noncancer etiology.[11] Opioid analgesics are considered the
cornerstone of cancer pain management, especially for the relief of
moderate to severe chronic pain.[12,13] Opioids act by
blocking the repeated transmission of pain signals and the resulting
neural remodeling underlying the pathophysiology of chronic pain
(discussed in detail below). Although the appropriate use of opioids can
lead to effective control of chronic pain, including breakthrough pain,
these drugs do not wholly eliminate the pain. The goal of therapy is the
control of pain and rehabilitation so that the patient can regain some
degree of their former functional status. Opioids are administered with
the aim of easing or reducing pain and suffering while improving
physical and mental functioning.[4]
For a variety of reasons, chronic pain
is often undertreated, particularly in the noncancer patient population.
Opioids are the strongest pain relievers available, but because of their
potential for abuse, they are classified as scheduled drugs by the US
Drug Enforcement Agency (DEA), under the Controlled Substances Act of
1970. The continued stigmatization of opioids and their prescription,
coupled with often unfounded and self-imposed physician fear of dealing
with the highly regulated distribution system for opioid analgesics,
remains a barrier to effective pain management and must be addressed.
Clinicians intimately involved with the treatment of patients with
chronic pain recognize that the majority of suffering patients lack
interest in substance abuse. In fact, patient fears of developing
substance abuse behaviors such as addiction often lead to undertreatment
of pain. The concern about patients with chronic pain becoming addicted
to opioids during long-term opioid therapy may stem from confusion
between physical dependence (tolerance) and psychological dependence
(addiction) that manifests as drug abuse. This misunderstanding can lead
to ineffective prescribing, administering, or dispensing of opioids for
chronic pain, resulting in undertreatment.
Nevertheless, the barriers to
effective pain management are slowly breaking down, especially in the
noncancer patient setting. Jointly, the DEA and 21 health organizations,
including the American Medical Association, have written a consensus
statement that supports the use of opioid analgesics for the treatment
of pain while recognizing their potential for abuse.[14] In
addition, many professional organizations, including the World Health
Organization (WHO), the American Pain Society, and the American Medical
Directors Association, have independently issued consensus statements
supporting the use of opioids in select patients with chronic noncancer
pain based on accumulated evidence indicating that patients treated with
opioids for chronic noncancer pain show improvement in analgesia and/or
level of function.
Thus, although state and local laws
restrict the medical use of opioids to relieve pain, awareness of and
adherence to these guidelines enables the physician to use these
effective agents in the management of chronic pain. Indeed, the Joint
Committee on Accreditation of Healthcare Organizations (JCAHO), which
accredits nearly 80% of the hospitals in the United States, has
developed standards for assessment and management of pain for patients
and has begun monitoring compliance with these standards.[15]
