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Therapies for Pain(2)

Blocks for Sympathetically Mediated Pain
--by Roger S. Cicala,M.D.

As discussed before, some cancer patients develop severe pain transmitted through the synpathetic nervous system (part of the nervous system controlling unconscious functions of the body, such as sweating or regulating blood flow through the tissue). The cause of sympathetic pain is not clearly understood, but it causes devastating pain if not treated effectively. Patients with bony metastases in in the extremities and those who have received radiation therapy are somewhat more likely to develop sympathetically mediated pain, but it has been caused by many other condition.
There is no test that clearly determines if a patient's pain is originating from the sympathetic nervous system. Some symptoms, such as a burning character to the pain, hypersensitivity of the skin in the affected area, and red or bluish discoloration, may hint that the pain is originating from the sympathetic nervous system. The condition may be the cause of pain that does not respond well to opiod medication.
When sympathetically mediated pain is suspected, a block of the sympathetic nerves can help to confirm the diagnosis and to treat the condition. Many different nerve blocks can be used for the treatment of sympathetically mediated pain. The most common are lumbar sympathetic blocks, stellate ganglion blocks, and Bier blocks.

Lumbar Sympathetic Blocks
A lumbar sympathetic block is used to disgnose and treat sympathetic pain originating from the foot or leg. From the patient's point of view, a lumbar sympathetic block is similar to an epidural block, with the needle placed in ghe lower back while the patient lies on her stomach, but the block is administered quite differently. When performing a lumbar sympathetic block, the doctor injects the anesthetic outside the vertebral column, which is the location of the sympathetic nerves.
When it is performed properly, a lumbar sympathetic block stops all activity in the sympathetic nerves to one leg, but does not interfere with the volunntary nerves. Since the voluntary nerves still function normally, there is no loss of sensation or weakness after the block. Because the sympathetic nerves do not function, the leg often becomes pink and warm as the blood vessels in the area dilate. If the block provides pain relief, that gives strong evidence that the sympathetic nervous system is involved in the pain. If the pain remains the same, then the sympathetic nervous system is probably not involved.
The pain relief following a lumbar sympathetic block is temporary, it may last for up to twelve to forty-eight hours. A series of three or four lumbar sympathetic blocks performed once every two or three days may give long-lasting relief. If the original block is not beneficial, however, there is no reason to repeat it.
When performed under fluoroscopic (X-ray) guidance, lumbar sympathetic blocks are considered very sage. Major complications are exceedingly rare, although some soreness in the muscles of the back should be expected for a day or two following the procedure.

Stellate Ganglion Block
For sympathetically mediated pain of the arm, head, or neck, a stellate ganglion block is performed. The stellate ganglion, also called the cervicothoracic ganglion, is a collection of nerve connections located outside in the spine near the base of the neck. The sympathetic nerves to the head, arm, and upper chest all originate from this area.
As with a lumbar sympathetic block, the injection of local anesthestic in this area stops activity in the sympathetic nerves without affecting motor or sensory nerves. Substantial pain improvement after a stellate ganglion block is evidence that the pain is mediated by the sympathetic nervous system. If the pain is relieved, a series of blocks is performed a described above.
Stellate ganglion injections require placing a needle into the base of the neck from the front. The patient is usually lying on his back during the injection, but a few doctors prefer to perform the procedure with the patient sitting up. Because the doctor can identify the stellate ganglion by touch, using X-ray is uncommon unless the patient is substantially overweight or has had extensive neck surgery in the past. The procedure can be performed quite quickly (often in only a minute or two) and typically gives very little discomfort.
Stellate ganglion injections are relatively sage in the hands of experienced physicians, but even in the best hands, some complications are possible. The Stellate ganglion is located very close to important structures in the neck, including the spinal nerve roots and the vertebral artery (an artery that passes up the neck to the base of the skull, eventually providing blood to the brainstem). It is possible for some of the local anesthetic injected during the procedure to reach either of these structures. Accidental injection into the vertebral artery could cause a seizures and loss of consciousness. Injection near a nerve root could cause a the anesthetic to block the higher parts of the spinal cord and brain, which also causes unconsciousness.

Bier Block
Bier blocks are a different method sometimes used to relieve sysmpathetically mediated pain. Bier blocks are simpler to perform and perhaps less uncomfortable than stellate and lumbar sympathetic block. They do have some limitations, however. For example, Bier blocks can only be used in the lower portion of the arm or leg (below the elbow or knee, respectively). Additionally, they cannot be used to diagnose sympathetically mediated pain, because the block also affects the voluntary nerves.
The procedure itself is quite simple. An intravenous catheter is placed into the hand or foot of the painfu limb. The arm or leg is then tightly wrapped in an elastic bandage, staring at the hand or foot and working toward the body, effectively squeezing most of the blood out of the limb. A blood pressure cuff or tourniquet is inflated to prevent the blood from returning to the extremity, including the branches of the sympathetic nerves.
Within a few minutes, the entire arm or leg becomes numb and remains so until the tourniquet is released (usually twenty to thirty minutes). Many studies using various combinations of local anesthetics and anti-imflammatory, antiseizure, and cardiac medications have been attempted with this technique. Although results are mixed, and no one medication is sympathetically mediated pain after treatment with Bier blocks.

Nerve Destruction Procedures

A nerve destructive procedure is essentially any technique that damages a nerve so that it can no longer function. There are several different methods used to damage a nerve, including thermal(heat or cold), electrical, chemical, and surgical. To treat cancer pain, the goal is to damage a nerve so that it can no longer transmit pain message to the spinal cord. Theoretically, this would relieve all the apin coming from the area served by the nerve.
On the surface, it would appear that nerve destruction procedures would be an ideal way to relieve cancer pain coming from a single area. Unfortuately, like so many issues in modern medicine, it is not that simple It is natural to assume that nerve destruction is the equivalent of a permanent nerve block, but this is not so. The actual during of a nerve destruction procedure may only last a few weeks and usually lasts less than six months. This impermanence occurs for two simple reasons: nerve repair and cancer progression.
Visualize a single nerve cell as a yo-yo dangling from a finger. The actual yo-yo is the nerve cell body and the string is the nerve fiber. In a human the cell body is located in or near the spinal cord, and the nerve fiber extends out into the arm, leg, chest, or face. When a doctor destroys a nerve in your arm or leg, he is actually damaging a large number of nerve fibers. The cell body remain undamaged in the spinal cord.
After the nerve fiber is damaged, the cell bodies attempt to repair the injury by growing a new nerve fiber along the path of the nerve. The growth process is both very slow and very chaotic. Because a single peripheral nerve contains thousands of fibers, the individual nerve fiber usually does not reconnect to its original location exactly. In some cases, a nerve fiber may reconnect to a slightly different area. In other cases, the new nerve fibers are unable to travel down the nerve and instead from a tangled ball-like formation within scar tissue, called a neuroma. As abnormal connections or neuromas are formed, the patient may begin to experience pain again. This may or may not be similar to the original pain, and over time, it may even become more severe than the original pain.
In addition to nerve regrowth, there is the issue of cancer progression. If it is not cured, camcer eventually speads, invading new structures. It the tumor grows into area not covered by the original nerve destruction procedure, the pain obviously will return.
Despite these limitation, nerve destruction procedures can be very useful in certain situations. Deciding when such procedures should be used involves considering the life expectancy of the patient and the possibility of cancer cure, understanding the nerve pathways carrying the pain signal, and the patient's ability to tolerate the predicted side effects. Nerve destruction should only be considered when the pain cannot be well controlled by using oral medications or other pain-relieving therapies. If there is significant chance that the paiful tumor can be cured, or at least reduced with radiation or chemotherapy, these methods should be tried before considering nerve destruction.
Nerve destruction is often very appropriate for patient who are in the terminal stages of cancer. Patients with advanced cancer often suffer severe pain that may require such high does of pain medication that they are always sedated. A nerve destruction procedure may allow the medication dose to be dramatically reduced, letting the affected person remain comfortable, yet alert enough to enjoy time with his loved ones. Since nerve destruction procedures often last for the life expectancy of a person with advanced cancer. Of course, predicting the duration of pain relief and life expectancy is as best educated guesswork, so repeat nerve destruction procedures may be necessary.
Since nerve destruction procedures only provide relief to a certain area of the body, they are not useful for patients suffering widespread pain involving large portions of their bodies. However, even such persons may have one or two areas that are much worse than pain in other area. Targetting these areas with nerve destruction techniques may reduce the pain level sufficiently to allow oral medications to provide of fective relief for the remaining pain.
In any case in which a nerve destruction procedure is being considered, a prognostic nerve block with local anesthetic should be performed first, so the patient can decide if a nerve destruction procedure is worthwhile. Some people fnd the numbness or weakness to be worse than the pain itself. Weakness, in particular, is often unacceptable to individuals who are already struggling to maintain some degree of personal freedom and self-care.

Nerve Destruction for Abdominal and Pelvic Cancer
Despite its drawbacks, nerve destruction can be a very valuable tool for controlling pain in properly selected patients. Most patients will undergo a trial injection wit local anesthetics prior to the actual nerve destruction procedure. If they do not receive pain relief with the local anesthetic block, there is no reason to believe that the neurolytic injection will give lont-term benefit.
Certain cancers located within the abdomen or pelvis, such as pancreatic cancer, cancer of the cerix, or bladder, respond very well to nerve destruction, because the nerves carrying pain signals from these locations are fairly easy to destroy. For example, most of the pain caused by pancreatic cancer is routed through a single nerve structure called the celiac plexus that is located between the spine and the abdomen.
The celiac plexus is a network of sensory nerves from the internal organs; it carries little or no motor information. When the plexus is blocked, patients with pancreatic cancer usually experience excellent pain relief without any numbness or weakness. Nerve destruction is performed almost identically to the standard celiac plexus block described earlier. Instead of injecting local anesthetic, however, a neurolytic chemical is used. Pure alcohol or phenol is the most commonly used chemical.
After destruction of the celiac plexus, most patients usually have at least 50 percent of their pain relieved. There may be some transient side effects, such as reduced blood pressure or diarrhea, but these usually subside after twenty to seventy-two hours. The beneficial effects of the procedure usually last about three months, but may last as long as six months. If the pain returns or intensifies, the procedure may be repeated, but repeated neurolytic injections are often less effective than the first block. This is because scar tissue forms around the plexus after the first injection. The scar tissue prevents the neurolytic chemical from spreading into the tissue with repeat injections.
Certain lower abdominal and pelvic cancers, such as bladder or uterine cancer, may also be treated with neurolytic injection. The procedure used, although very similar to a celiac plexus injection, targets a different group of nerves called the hypogastric plexus. This plexus is located in front of the lowest bones of the spine. The success rate of hypogastric plexus block is somewhat less than celia block, but the complication rate of the procedure is low.

Peripheral Nerve Destruction
Unfortuately, most peripheral nerves carry both motor and sensory information. A permanent block with alcohol or phenol will destroy at least some of the motor nerve fibersm causing weakness or even complete paralysis. For patients with advanced cancer, this loss of motor function may be unimportant when compared to achieving better pain control. However, some individuals may find the persistent numbness or weakness unacceptable. For this reason, it is crucial that patients receive a trial of local anesthetic injections prior to undergoing a more permanent procedure.
The most common locations for peripheral neurolytic injections are the face, neck, and rib cage. Facial injections may provide the most dramnatic pain relief, but can also have the most significant side effects because of motor weakness. Depending on the exact nerves involved, side effects could include difficulty speaking, chewing, and swallowing. In a few rate cases, severe skin damage or complete loss of jaw muscle control has occurred.
Injection of the chest wall is also very helpful and is associated with far fewer side effects. There is a small (less than 1 percent) chance that a chest wall injection could cause a collapsed lung. If a collapsed lung occurs, it might be necessary to insert a small tube through the chest wall to reexpand the lung, and a hospital stay of serval days could be required. This certainly not a minor complication, but almost all patients who suffer lung collapse recover without any significant permanent injury. As with most nerve destruction procedures, the risk is slight when compared to the potential pain relief that could be obtained.
Some peripheral nerves, particularly the ones in the chest wall, can be blocked with a special technique called Cryoanalgesia, which means freezing the nerve. Cryoanalgesia is performed just like other nerve blocks, but instead of injecting medication, a special needle-shaped probe that can rapidly freeze tissues is used. Cryoanalgesia destroys the nerve, although not as completely as a neurolytic injection. It can provide weeks or even months of pain relief and can be repeated more easily than chemical injection, since it causes less scarring. Cryoanalgesia equipment is bulky and costly, however, so it is not always available. Because the probes are somewhat larger than regular needles, it is not appropriate for some of the other nerve destruction procedures.

Neurodural Destruction of Spinal Cord Nerve Tracts
Historically, ablative(destructive) neurosurgical procedures were often performed on the spinal cord to relieve the most severe types of cancer pain. These interventions are used much less frequently today, having been replaced by better medications, nerve blocks, and intraspinal medications. Neverthelss, a few patients are still appropriate candidates for these ablative operations.
Many different ablative procedures can be used to treat cancer pain. Perhaps the most frequently used hitorically, and still the most useful today, is the cordotomy. In this operation, a small part of the spinal cord is cut surgically or burned with a radio frequency(similar to microwave)needle. The part of the spinal cord that is destroyed is called the lateral spinothalamic tract. The lateral spinothalamic tract is the bundle of nerve fibers that carries painful sensations up the spinal cord to the part of the brain called the thalamus. The procedure can be performed through a very small incision, so general anesthesia is not usually required.
Cordotomy is most effective for pain originating in the leg and hip on one side of the body. It is less effective at relieving pain originating in the arm or the trunk. Cordotomy is also much more effective for controlling somatic pain and usally not effective against neuropathetic pain. After the procedure has been done, the patient will have some numbness on the side of the body on which the procedure was performed.
The location of the spinothalamic tract within the spinal cord must be estimated when a cordotomy is performed. Although this estimation can be done quite accurately(to a small fraction of an inch), the spinal cord is densely packed with other fiber tracts involved in other functions. It is possible that some of these other tracts could be injured during cordotomy, resulting in difficulty controlling bladder or bowel, function, or weakness of the leg on the involved side. These complications are more common when cordotomy is performed on both sides of the spinal cord, as must be done if the pain involves both sides of the body.
Because of the potential complications, cordotomy is usually performed only for patients who either have leg pain on only one side, or who already have lost control of their bowels and bladder. Finally, a significant number of patients will experience return of their pain after six or eight months. For this reason, the procedure is usually reserved for terminal patients.