Cancer-associated pain continues to be a significant predicament in the treatment of malignant syndromes and adversely affects quality of life. The prevalence of cancer-associated pain is highly variable and is contingent on type of malignancy and stage of disease. Reports of the prevalence of cancer-associated pain range anywhere from 33% to 50% and can reach greater than 70% among patients with advanced disease. Poor pain control has been shown to increase hospitalizations, emergency room visits, physician utilization, and overall cost of healthcare. The importance of effective pain control among cancer patients contributes to the coping process related to the stressors of the disease and its treatment.
The diverse character of cancer-associated pain can be categorized by descriptors such as those related to temporal characteristics, predominating pain mechanisms, and underlying etiology. Temporal characteristics include distinction between acute and chronic. Acute pain is associated with a particular event that lasts from seconds to a few weeks. Pain persisting longer than 3 months is labeled as a chronic process. Most patients with chronic cancer pain have superimposed episodes of acute pain termed “break through pain.”
Cancer pain is also classified by mechanism as nociceptive, neuropathic, or a combination of both. Nociceptive pain results when nociceptors detect noxious mechanical, chemical, and thermal stimuli and generate neuronal electrical activity. Nociceptive pain can further be subcategorized as somatic or visceral. Somatic structures include skin, muscle, bone, and fascia. Innervation of somatic structures is extremely specific and localization is defined. Somatic pain is mediated by the somatic nervous system. Internal organs generate visceral pain and are mediated by the autonomic nervous system. Visceral pain lacks specificity as compared to somatic pain and is difficult to localize and may encompass an area much larger than the affected organ. Nociceptors are also activated with visceral pain but the vague sensation is due to the low number of nociceptors and the extensive divergence of visceral input within the central nervous system. In addition visceral pain can also refer to various parts of the anatomy secondary to the convergence of visceral afferent fibers entering the spinal cord at the same level as somatic structures.
Neuropathic pain occurs when the principal injury occurs in the nervous system. The injury can be either peripheral or central. The nervous system is subject to injury via a number of mechanisms such as damage from compression, infiltration, ischemia, metabolic injury, or transection. Neuropathic pain can undergo central facilitation known as wind-up which can lead to exaggerated perceptions resulting in hyperalgesia and allodynia.
MANAGEMENT OF CANCER-ASSOCIATED PAIN
In 1988, the World Health Organization first devised the three-step ladder for the management of cancer-related pain (Figure 123-1). The ladder is an excellent tool for initiating analgesic selection based on pain severity. Many studies have shown the achievement of adequate analgesia in up to 90% ...