Endometriosis: Interactive Support & Information

Acute Versus Chronic Pain

By Julie Zimmerman, PT

"Illness is the most heeded of doctors: to goodness and wisdom we only make promises; pain we obey." --Marcel Proust

Acute pain is a normal, protective response to alert the body to possible tissue damage. It is an unpleasant sensation, from discomfort to agony, caused by the stimulation of specialized nerve endings. Pain is primarily associated with physical injury, but since pain is a perception it may not be proportional or even directly related to an injury. The experience of hurting is a composite of physical, intellectual, emotional, motivational and situational reactions. Factors other than tissue damage may directly affect
the severity, tolerance and persistence of symptoms. In addition, pain does not necessarily correspond to the damaged area; it may move or change, and may or may not follow expected patterns of radiation. These are among the many reasons that pain may not be an accurate measure of the location and severity of an injury. They all need to be taken into consideration in the diagnosis and treatment of back pain.

Pain: An Unreliable Indicator of Pathology
"Pain is perception. Therefore all pain is in the brain." -- American Osteopathic Association
1) Pain is highly subjective and influenced by emotional, intellectual and situational factors. A child may perceive the pain of a skinned knee differently in the presence of friends than in the company of his doting grandparents. 2) Accuracy of pain localization depends on nearness of the injury to the body surface. The pain from a rapped shin bone is well defined compared to the diffuse ache of an intestinal upset. 3) Pain perception does not necessarily correspond to the site of stimulation; pain can be referred to other structures. During a heart attack, severe pain may be felt down the left arm. 4) Different structures have different sensitivities to pain. 5) Severe pain in one structure can block pain from another structure. When someone stubs a toe, the pain from a headache is temporarily forgotten. 6) Pain is blocked by sensory stimulation. When an individual bangs her head, her tendency is to rub it. 7) Pain can radiate, following nerve, muscle or embryological patterns of distribution. "Sciatica" is felt as pain down the back of the leg, but it usually indicates a problem in the lumbo-sacral spine. 8) Painful structures can increase pain perception or can block pain in other structures from the same embryological segment. 9) Pain perception can depend on the temporal or spatial summation of stimuli. An individual can comfortably perform may repetitions of a specific exercise and then suddenly feel pain the next time the motion is repeated. 10) Pain is inconsistent and may change in location and severity. The ache of an arthritic hip may wax and wane throughout the day for no apparent reason. 11) Pain is strongly influenced by the "placebo effect," the relief of symptoms caused only by the belief that one is receiving a pain-relieving treatment. The placebo effect may work through the production of "endorphins," the body's natural pain killers. 12) Pain can persist after its organic cause has been treated and thought to be corrected. A whiplash injury may result in chronic pain despite the fact that no evidence of tissue damage remains.

Pain Sensitivity in Spinal Tissues

Some spinal structures are essentially without pain receptors; these include intervertebral disks, cartilage, vertebral bodies (unless invaded by cancer) and nerve roots. Pain responsive tissue (in the approximate order of sensitivity) includes the periosteum (outer covering of bone), joint capsules, synovial lining, ligaments, subchondral bone (bone which lies beneath cartilage), tendons, nerves and nerve sheaths, fascia (connective tissue), cortical bone ("one which composes the outer layer of the shaft) and muscles.

In back dysfunction, the structures that usually give rise to pain are the anterior and posterior longitudinal ligaments, the outer covering of the nerve roots (the dura), the spinal muscles, the fascia of the muscles, the facet joints and the sacroiliac joints.

Gate Control Theory

Pain travels in small nerve fibers; it is usually blocked at the spinal cord by a steady volume of large fiber (sensory) impulses. When a strong enough painful stimulus occurs, the message of pain from the small pain fibers blocks the large fiber transmission to reach the brain and consciousness. Pain which would normally reach someone's awareness can in turn be blocked by increased levels of sensory stimulation. This view of pain perception is called gate control theory and this may be why both acupuncture and TENS can provide relief.

Embryological Pain Patterns

Pain patterns associated with deep injury may be related to the embryological development of the musculoskeletal system. When one structure is injured, other structures which originated in the fetus from the same mass of tissue are affected. The results may include an embryological pattern of increased muscle tone, hyperactive reflexes and increased skin sensitivity.

The Classification of Pain
"The Greeks viewed pain as an experience resulting from some failure in the right process of living." Steven Brena, MD There are three kinds of pain. Back pain can fit into any one of these categories; it is one type of pain that does not necessarily correspond to the site of tissue damage or extent of an injury. 1) Transient pain is of short duration and serves as a warning signal, such as with a stubbed toe or from touching a hot stove. 2) Acute pain is secondary to specific tissue damage such as with a sprained ankle or stomach ulcer. 3) Chronic pain is caused by persistent disease such as rheumatoid arthritis, or it is a condition which lasts beyond the expected recovery time.
The type of pain which causes the most puzzlement and frustration to both patient and practitioner is chronic pain, where the pain persists after the physical cause has been treated and considered corrected. A back condition becomes "chronic" after a maximum of six months; some call it chronic after three months or even six weeks. The pain is constant, waxing and waning but seldom disappearing, and doesn't respond to treatment. To all appearances the patient's clinical picture improves with no remaining evidence of injury, but the symptoms do not As much as 35 percent of the adult population may experience chronic pain for a significant period of their lives; 10-15 percent of Americans may suffer from pain at any one time. Back pain is the most common kind of chronic pain.

The Causes of Chronic Pain

"We have no business calling a patient a malingerer just because we cannot find a physical basis for his pain or because he's had it for a very long period." Stanley Pans, PT.

It is not known why some people's pain lasts far beyond the expected recovery period. Five possible explanations follow: 1) Chronic pain may be explained as continuing pathology of spinal structures which has not yet been identified. Given the difficulty in diagnosing back pain, this is not an unreasonable option. 2) Chronic pain may result from a change in the nervous system's transmission of pain messages; cells that normally fire once start to respond excessively to minor, innocuous stimuli. The continuing barrage of pain impulses eventually may break down the brain or spinal cord mechanisms which would normally block perception of minor pain impulses. The pain becomes less and less associated with a physical basis as time goes by. 3) The body's physical response to acute injury can perpetuate chronic pain. Back muscles go into spasm to splint and protect a spinal injury, causing a build-up of toxins, decreased blood flow and eventually stiffness and reduced activity; all of these conditions can themselves produce pain. Emotional responses to being in pain also increase muscular tension. The persistence of symptoms is exhausting, but sleep is disturbed by the pain and anxiety, increasing fatigue. All these factors create a cycle of anxiety, muscle tension and pain, each perpetuating the others.' 4) Chronic pain may be due to the postural adjustments which are made in response to an acute injury; these myofascial compensations are made in an attempt to relieve pain and may then become habit. Postural muscles no longer relax or contract efficiently and are not recruited in their normal patterns of movement. The original injury may be resolved, but the pain is perpetuated by the postural dysfunction. 5) Many practitioners specializing in the treatment of chronic pain believe that its explanation lies in a patient's emotional make-up. The theory that chronic pain is psychogenic versus somatogenic, (originating in the mind versus the body), or that it is perpetuated by emotional factors is well-established in the chronic pain field.

A generalized explanation of chronic pain applied to back dysfunction might be as follows. Chronic back pain usually begins with injury or strain of spinal structures, but it becomes a disorder in and of itself with both physical and psychological characteristics. Normal responses to physical pain, (muscle spasm, restricted activity, postural compensations, anxiety, depression and fatigue), can initiate a cycle which helps to perpetuate the pain. Eventually, pain perception may be maintained by the nervous system with little input form the original site of injury. Whatever is happening on a physical level, the pain has stopped serving a useful purpose in protecting the body. Key Points - Acute Versus Chronic Pain

Pain is a normal protective mechanism of the body which signals potential tissue damage. However, pain is not a reliable guide to the location and extent of an injury. Chronic pain occurs when symptoms persist long after an injury, with no remaining physical evidence of tissue damage. Different theories are put forth explaining the development of chronic pain.

Reprinted with permission