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Thalamic Pain Syndrome

The thalamic pain syndrome is a poorly understood phenomenon that occurs as a later complication of a small stroke in a very particular area of the brain known as the thalamus. The syndrome is characterized by chronic pain occurring on the same side of the body that is affected by the stroke, opposite the side of the brain that the stroke occurred in.

Deep beneath the surface of each of the two globe-like halves of the brain is a group of berry and nut-sized clusters of brain cells collectively known as the basal ganglia. One of the more central of these clusters is called the thalamus. The thalamus acts as a central processing center for sensory information streaming toward the brain from the rest of the body. Sensory information such as touch, pressure, heat, cold, and pain travels along nerves from all parts of the body into the spinal cord, where it travels upward along specialized pathways, or tracts, toward the brain. As all of the various sensory tracts enter the brain through the brainstem, they converge upon the thalamus, which processes and integrates the multitude of sensations, and then relays them to appropriate areas of the brain where the information is used or brought into the individual's conscious awareness.

It is important to note that, as the sensory tracts ascend toward the brain, most cross over at some point to the opposite side of the spinal cord or brainstem. For instance, pain sensation from the right hand travels via sensory nerves to enter the right half of the spinal cord, travels a short distance upward in a tract which then crosses over to the left half of the cord to finally deliver the sensory pain message to the left thalamus in the left side of the brain. Thus, a pinprick on the right hand is appreciated mostly in the left half of the brain.

The deep structures of the brain, including the basal ganglia, receive their blood supply from very small, almost hair-thin arteries, called arterioles. Occlusion or blockage of one or more of these arterioles can occur for a variety of reasons, resulting in a small deep stroke often referred to as a "lacunar stroke" or "lacunar infarction." Lacune means "lake" or "hole." Most strokes affecting the thalamus and producing the pain syndrome are of this type. Not all strokes involving the thalamus produce this syndrome, which typically develops weeks or even months after the event. The exact reasons why some thalamic strokes produce it are not well understood.

A small stroke confined mainly to the thalamus will initially produce some loss of sensation on the opposite side of the body. If the stroke damages adjacent brain structures involved in motor function, some degree of paralysis or weakness can occur on the opposite side as well. Typically, the lost functions will partially recover over time. In a few cases, even if the recovery is nearly complete, the pain syndrome begins to develop. It may start as a vague uncomfortable sensation such as stinging of the skin. It may be confined to one limb or to half of the face, or may involve the entire half of the body including face, torso, and limbs. This may progress to true pain, sometimes excruciating in intensity. The character of the pain varies among individuals, and may be described as a burning hot sensation, shooting or lancinating pain, or even feelings of the skin being scratched and torn. The pain is usually unrelenting, present to some degree during all waking hours. In many cases, the normal perception of innocuous sensations may become altered; an individual may perceive light touches, the rub of clothing, or even drafts of air as irritating or painful on the involved side, a condition referred to variously as hypersensitivity, hyperpathia, allodynia, or dysesthesia. The pain syndrome may improve over time, but is often permanent.

The presentation of the thalamic pain syndrome can be confounding to medical practitioners. The usual course is to search for a cause of pain in the limbs, such as arthritis, skin conditions, or pinched nerves. When no physical cause is turned up after exhaustive examinations, the practitioner may characterize the pain as psychological or psychosomatic in nature. The irony is that when a doctor labels the pain as being "all in the patient's head," he is not making an incorrect statement. The pain does indeed originate in the thalamus, inside the brain—it is merely perceived by the patient as being located in the involved body parts. Once a diagnosis is made, usually by a physician experienced in the long-term care of stroke survivors, appropriate therapy can be initiated.

Unfortunately, there is no single efficacious treatment for this disorder. Traditional oral pain medications such as acetaminophen (Tylenol), ibuprofen (Advil, Motrin), naproxen (Naprosyn, Anaprox, Aleve) have limited effect. Combinations of these medications with narcotic analgesics such as codeine or hydrocodone (Vicodyn and others) are somewhat more effective if side effects can be tolerated.

There has been moderate success in recent years with the use of non-traditional or atypical pain medications. These are medicines that were developed to treat other medical conditions such as epileptic seizures or depression, and are now being discovered to have efficacy in the treatment of neurological causes of pain. Amytryptiline (Elavil) and similar antidepressants are used, and early side effects such as dry mouth and sedation can usually be overcome with judicious management. Epileptic seizure drugs are showing even more promise, sometimes with fewer side effects. The most popular of these is gabapentin (Neurontin), and others are slowly coming into use.

The principle followed in application of the non-traditional medications is "Start low and go slow." The drugs are initiated at low doses and gradually increased over weeks to allow the patient to develop tolerance to the side effects. The effect of these medications is not immediate; a patient cannot simply take a tablet during a bout of severe pain and expect the pain to be alleviated. Typically, a patient must have been taking an appropriate dose for a week or weeks for the full beneficial effect to occur. Thus a trial of any one of the medications can take months. If one medication does not work or is not tolerated due to side effects after an appropriate trial, then another medication must be chosen and tried. The finding of a best treatment therefore requires patience and perseverance from the patient and the physician. The goal of oral medicinal therapy is not to eliminate the pain, but to make it manageable and tolerable.

Some specialized pain management centers are applying a variety of aggressive procedures for thalamic pain which are too involved to discuss at length here. All have had variable success. These techniques may include implanted pumps to deliver medication into the spinal canal, surgical destruction of areas of the thalamus or basal ganglia near the stroke, or implantation of a wire which delivers low level electrical current to the basal ganglia in an attempt to block pain signals from the thalamus to the rest of the brain.

Mayank Pathak, M.D.

SAFE (Stroke Awareness for Everyone, Inc.) has been given permission to reproduce this article by its author, Mayank Pathak, M.D. Dr. Pathak is Staff Physician, at The Parkinson's and Movement Disorders Institute, Fountain Valley, California.

Learn more about and find support for Thalamic and Central Pain at the following website: Central Pain Syndrome Alliance (CPSA).

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