Pain: Moving from Symptom Control toward Mechanism-Specific Pharmacologic Management

Pain: Moving from Symptom Control toward Mechanism-Specific Pharmacologic Management

Clifford J. Woolf, MD

From Neural Plasticity Research Group, Massachusetts General Hospital and Harvard Medical School, Charlestown, Massachusetts.

PHYSIOLOGY IN MEDICINE: A SERIES OF ARTICLES LINKING MEDICINE WITH SCIENCE

Co-sponsored by the American College of Physicians and the American Physiological Society

Physiology in Medicine: Dennis A. Ausiello, MD, Editor; Dale J. Benos, PhD, Deputy Editor; Francois Abboud, MD, Associate Editor; William J. Koopman, MD, Associate Editor

Annals of Internal Medicine: Paul Epstein, MD, Series Editor

Clinical Principles

Nociceptive pain: transient pain in response to a noxious stimulus.

Inflammatory pain: spontaneous pain and hypersensitivity to pain in response to tissue damage and inflammation.

Neuropathis pain: spontaneous pain and hypersensitivity to pain in association with damage to or a lesion of the nervous system.

Functional pain: hypersensitivity to pain resulting from abnormal central processing of normal input.

Physiologic Principles

Nociception

Peripheral sensitization

Phenotype switch

Central sensitization

Neuron glial interaction

Increased facilitation

Structural reorganization

Decreased inhibition

Pain is a multidimensional sensory experience that is intrinsically unpleasant and associated with hurting and soreness. It may vary in intensity (mild, moderate, or severe), quality (sharp, burning, or dull), duration (transient, intermittent, or persistent), and referral (superficial or deep, localized or diffuse). Although it is essentially a sensation, pain has strong cognitive and emotional components; it is linked to, or described in terms of, suffering. It is also associated with avoidance motor reflexes and alterations in autonomic output. All of these traits are inextricably linked in the experience of pain.

Although we tend to think of pain as a homogeneous sensory entity, several distinct types exist: nociceptive, inflammatory, neuropathic, and functional (Figure 1). The neurobiological mechanisms responsible for these different pains are beginning to be defined (1-3), providing insight into how distinct types of pain are generated by diverse etiologic factors, and in which patients (4). Moreover, we can now realistically expect to move from an empirical therapeutic approach to one that it is targeted specifically …

[Full Text of this Article]