The Different Kinds of Pain
It is not intuitively obvious, but pain is not the same experience every time it occurs. A person can experience many different kinds of pain, partly because different parts of the body tend to cause or create different types of pain. Although severe stomach cramps and a toothache are both causes of pain, there are differences between those pains that are more than just the difference in location and intensity. Doctors classify pain into several broad caregories to better understand what is causing pain and, more importantly from the patient's standpoint, how to treat it.
One way to separate the types of pain is by location, but from a treatment standpointŁ¬this is not very useful. There is far more difference between toe pain and stomach pain than there is between toe pain and finger pain. It is more helpful to separate pain according to the kind of organ or tissue that the pain originates from, and the nerves involved in carrying the pain message. This kind of classification usually divides pain into five broad categories: somatic, visceral, neuopathic, central, and sympatheric types of pain. Each type has very different characteristics and may respond to different treatments, so each will be discussed separately.
In s complex disease, such as cancer, a person may suffer from more than one type of pain. It is important to understand each separate cause of a person's pain, since pain relief can only be achieved when each type is treated successfully. For example, a morphinelike medication should effectively relieve somatic pain from a bone, but will not help with certain other type of pain. If nothing is done about those other pains, the person still hurts, still can't sleep, and still has all the suffering that comes from chronic pain.
Somatic pain originates from the skin, muscles, tendons, ligaments, and bones. One can easily pinpoint the exact location of somatic pain, which is often sharp, stabbing, throbbling, or aching in nature. When you cut your finger with a knife, you know exactly where it hurts, even without looking, and exactly what the pain feels like. To some degree, thesetissues can also cause referred pain (pain that is felt somewhere besides the actual point of damage), but when this does occur, the referred pain is typically located very close to the point of actual injury.
The parts of the body that cause somatic pain are particularly well monitored by the brain because they are so important to how we interact with our environment. You have to know where your feet are to walk without falling. In contrast, we don't realy need to sense exactly where our spleen is located to perform everyday activities. The ability to describe exactly where the pain is coming from is handy when you need to take a splinter out of your finger. It also makes it fairly easy for your doctor to diagnose the cause of somatic pain.
Although somatic pain can be severe, it tends to respond very well to a number of different medications and therapies. Most of the medicines created for pain relief work best to treat somatic pain. This includes medicines ranging from acetaminophen (Tylenol) and aspirin to codeine, Demerol, and morphine, among others. The effectiveness of any one of factors. These include the severity and actual cause of the pain, the person's individual response to the medication, and probably even the individual's genetic makeup.
Visceral pain is generated by the internal organs of the body such as the liver, intestines, or stomach. Visceral pain is often most severe when an organ is distended or swollen. In contrast to somatic pain, visceral pain tends to be poorly localized and more likely to generate referred sensations remote from the actual site of injury. The diffuse nature of this pain can make the diagnosis of its cause difficult and frustrating for both physicians and patients.
Luckly, some aspects of visceral pain can help identify its source. The hollow organs, like the intestines, typically generate an intermittent, cramping pain that may or may not have an underlying steady, dull pain. The solid organs, such as the spleen, usually cause a dull aching pain or pressure sensation. In addition, while the location of referred visceral pain cannot identify the structure causing the pain as exactly as somatic pain does, the pain does tend to follow certain general patterns. For example, an inflamed appendix usually first causes pain around the navel region. Later, when the wall of the abdomen overlying the appendix becomes irritated, the pain is felt in the right lower part of the abdomen where the appendix actually exists. Other common patterns of regerred visceral pain are also known. Pain from the pancreas tends to radiate from the stomach straight through to the back, whereas irritation of the diaphragm (the main breathing muscle) is felt more in the shoulder. Unfortunately, these patterns are only helpful in general terms. When a person suffers a visceral pain, there are usually several different organs that might be the cause of that pain.
Cancer may cause visceral pain when a tumor invades an internal organ or presses on nearby organs. The treatment of visceral pain may involve medications, but routine pain medications are not as effective for visceral pain as they are for somatic pain. Fortunately, visceral pain associated with cancer often responds well to the destruction of specific nerve structures.
It is relatively common for somatice pain and visceral pain to exist together. For example, a tumor from the colon or prostate that has metastasized (migrated) to a bone will cause both visceral pain from the original tumor and somatic pain from the metastasis.
Neuropatbic pain occurs when the nerves themselves are damaged. This may happen when a tumor invades a nerve, when an episode of shingles destroys some f the nerve fibers, or when some structure presses on the nerve. Radiation and chemotherapy can sometimes cause neuropathic pain, although that condition is usually temporary.
Compared to other types of pain, neuropathic pain is typically more burning in nature, although it may also be perceived as aching. The area involved in neuropathic pain often has allodynia (hypersensitivity) even to a light touch. Some patients have lightning, or electrical shocklike spams of pain that last for only a second or two, but which are dramatically more intense than the background pain. This has been termed lancinating pain and may require different treatments than the background pain.
Although it is sometimes convenient to compare nerves to the coper wiring in a house, the nervous system is made up of living tissue. As discussed earlier, there are several different types of nerve fibers. Damage to a nerve may completely destroy some fibers, but only injure others. The injured fibers may send abnormal signals that the brain perceives as a pain message, even though there is no "real" cause of pain in the tissues. Since some other fibers in the same nerve may be completely destroyed, it is not unusualy for a patient to experience both numbness and pain in the same location.
There are two broad categories of neurioathic pain involving he peripheral nerves. Injury to a single nerve is often termed neuralgic pain. It can be caused by anything that damages the nerve, such as surgery, radiation, or invasion by a tumor. The other type of neuropathic pain can be caused by anything that mildly damages all the nerves in the body.s usually most affected. Since the longest nerve fibes usually receive the most damage, the nerves to the feet and hands are usually most affected. This type of neuropathic pain, called peripheral neuropathy, causes a severe burning pain in both feet and sometimes both hands. Some forms of chemotherapy can cause peripheral neuropathy.
Neuropathic pain is not common in cancer patients, which is fortuate, because it is much different to treat than either somatic or visceral pain. For example, morphine, which works well for many kinds of cancer pain, is sometimes completely ineffective for treating neuropathic pain. Fortuately, there are medicines that have been "borrowed" from other uses to treat neuropathic pain. These include drugs normally used to treat depression or serzures. Additionally. nerve blocks and the injection of steroids (cortisone) near the affected nerves can dramatically improve some types of neuropathic pain. In more difficult cases, therapics such as nerve stimulation and certain nerve-destroying procedures may be attempted.
Central pain is similar to neuropathic pain in that it involves damage to nerve cells. In this condition, however, the damaged nerve cells creating the pain are located either in the brain or in the spinal cord. Central pain syndrome is rare. It usually occurs only after certain types of stroke or when brain tumors (including metastasis) involve certain areas of the brain. It often causes a widespread pain similar in nature to neuropathic pain, but very difficult for the patient to describe. It may also cause large areas of the body to become hypersensitive to pain.
Central pain can be extremely difficult to treat, although it sometimes responds to antiseizure medications and antidepressants. Certain neurosurgical procedures may also be effective.
Sympathetically Mediated Pain
This type of pain does not have anythin to do with feeling sympathy for anyone; it simply refers to the sympathetic nervous system, part of the nervous system that controls involuntary or unconscious functions of the body. The involuntary nervous system is divided into two subclasses, thw sympathetic and parasympathetic systems. These systems act in oppositions. The sympathetic nervous system controls such functions as sweating, the actions of the intestines and internal organs, dilation and ontractions of the pupils in the eye, and blood flow through various tissues.
regional pain syndrome, and sympathetically mediated pain. Although there are slightly differnt definitions for these terms, in general they all refer to abnormal pain originatingg from the sympathetic nervous system.
The mechanism by which sympathetically mediated pain occurs is complex and not fully understood. The symptoms, which usually begin in a foot or hand, are often dramatic. Sympathetic pain has a severe burning characteristic, usually without any aching or shocking sensations. The affected are is hypersensitive to even the lightest touch. Pink or bluish discoloration of the involved area may occur because of abnormal circulation, and abnormal sweating may be noticed in the affected area.
Like many pain syndromes, sympathetic pain is not direcwtly caused by cancer but can result as a consequence of the cancer or cancer treatment. While uncommon, it is most likely to occur in persons who have either primary or metastatic cancer involving the extremities. It may begin after tumors invading the bones cause fractures of the arms or legs after amputation of an extremity in an attempt to contain the speed of cancer, or without any apecific inciting event.
Sympahetic pain responds to pain medications to some degree, but is usually treated more effectively with nerve blocks or destruction of the sympathetic nerves going to the affected area. Since these nerves do not carry normal sensations, there is usually no long term effect fro destroying them. Unfortuately, the procedures are not always successful in relieving the pain.