Chronic pain is defined as pain that persists longer than the temporal course of natural healing, associated with a particular type of injury or disease process
The International Association for the Study of Pain defines pain as “an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.” Pain is subjective in nature and is defined by the person experiencing it, and the medical community’s understanding of chronic pain now includes the impact that the mind has in processing and interpreting pain signals.
Functional Anatomy
The anatomy of the nociceptive system can be grossly divided into the peripheral and central nervous system. The peripheral nervous system consists of small myelinated and unmyelinated nerve fibers. These nerve fibers converge into a region of the spinal cord referred to as the dorsal horn. The dorsal horn is the first relay station in pain signal transmission. The next element of pain transmission includes nerve fibers that then travel to the thalamus. From the thalamus the next order of neurons ascend to the limbic system and sensory cortex. This accounts for the affective elements and discriminative of pain respectively.
Nociception
Nociceptors convey information regarding damage or trauma from the body to the central nervous system, a process called nociception, where it is interpreted by the brain as pain. Nociception occurs in any tissue or organ in which pain signals arise secondary to a disease process or trauma. If the pain occurs due to dysfunction or damage to nerves themselves, it is called neuropathic pain.
Pathophysiology
Under persistent activation nociceptive transmission to the dorsal horn may induce a wind up phenomenon. This induces pathological changes that lower the threshold for pain signals to be transmitted. In addition it may generate nonnociceptive nerve fibers to respond to pain signals. Nonnociceptive nerve fibers may also be able to generate and transmit pain signals. In chronic pain this process is difficult to reverse or eradicate once established.
Classification
Nociception (pain) may arise from injury or disease to visceral, somatic and neural structures in the body. More broadly pain is described as malignant or non-malignant in origin.
Diagnosis
Pain may be a response to injury or any number of disease states that provoke nociception. Advances in imaging studies and electrophysiological studies allow us to gain a deeper insight into the characteristics and properties associated with the phenomenon of chronic pain.
Some chronic pain may be psychosomatic. Indicators include diffuse, difficult to describe symptoms, especially if they moved around the body and have no obvious verifiable physical cause. Having unexplained pain in three or more body parts is especially indicative.
Rehabilitation
As alluded to earlier there are other modalities used in the treatment of chronic pain. These include: physical modalities such as thermal agents and electrotherapy. Complementary and alternative medicine, therapeutic exercise and behavioral therapy are also utilized autonomously or in tandem with interventional techniques and conventional pharmacotherapy. This is most often structured in a multidisciplinary or interdisciplinary program.