Pain is an important sign of illness, and it stands preeminent among all the sensory experiences by which humans judge the existence of disease within themselves. Indeed, pain is the most common medical symptom. Relatively few diseases do not have a painful phase and in many, pain is a characteristic without which diagnosis must be in doubt.
The painful experiences pose manifold problems in virtually every field of medicine; physicians must therefore be prepared to recognize disease in patients who have felt only the first rumblings of discomfort, before other symptoms and signs have appeared. Even more problematic are patients who seek treatment for pain that appears to have little or no structural basis; further inquiry may disclose that fear of serious disease, worry, or depression has aggravated some relatively minor ache or that the complaint of pain has become the means of seeking attention, drugs or monetary compensation. They must also cope with the "difficult" pain patients in whom no amount of investigation brings to light either medical or psychiatric illness. Finally, the physician must be prepared to manage patients who require relief from intractable pain caused by established and incurable disease. To deal intelligently with pain problems requires familiarity with the anatomy of sensory pathways and the sensory supply of body segments as well as insight into the psychological factors that influence the perception of and reaction to pain.
The ambiguity with which the term pain is used is responsible for some of our difficulty in understanding it. One aspect, the easier to comprehend, is the transmission of impulses along certain pathways in response to potentially tissue-damaging stimuli, i.e., nociception. Far more abstruse is its quality as a mental state intimately linked to emotion, i.e., the quality of anguish or suffering—"a passion of the soul," in the words of Aristotle—which defies definition and quantification. This duality (nociception and suffering) is of practical importance for certain drugs or surgical procedures, such as cingulotomy, may reduce the patient's reaction to painful stimuli, leaving awareness of the sensation largely intact. Alternatively, interruption of certain neural pathways may abolish all sensation in an affected part but the symptom of pain may persist (i.e., denervation dysesthesia or anesthesia dolorosa), even in an amputated limb ("phantom pain"). Finally, unlike most sensory modalities—which are aroused by a specific stimulus such as touch-pressure, heat, or cold—pain can be evoked by any one of these stimuli if it is intense enough.
It is apparent to us that in highly specialized medical centers, and often even in "pain centers," few physicians are capable of handling difficult and unusual pain problems in any comprehensive way. In fact, it is to the neurologist that other physicians regularly turn for help with these matters. Although much has been learned about the anatomy of pain pathways, their physiologic mechanisms, and which structures to ablate in order to produce analgesia, relatively little is known about which patients should be subjected to ...