Central pain syndrome

Definition

Central pain syndrome is a type of pain that occurs because of injuries to the brain or spinal cord.

Description

Central pain syndrome can occur in conjunction with a number of conditions involving the brain or spinal cord, including stroke ; traumatic injury to, or tumors involving, the brain or spinal cord; Parkinson's disease ; multiple sclerosis ; or epilepsy .

The pain of central pain syndrome is an extremely persistent, intractable type of pain that can be quite debilitating and depressing to the sufferer. The pain may be localized to a particular part of the body (such as the hands or feet), or may be more widely distributed. The quality of the pain may remain the same or may change. Some of the types of pain experienced in central pain syndrome include sensations of crampy muscle spasms; burning; an increased sensitivity to painful stimuli; pain brought on by normally unpainful stimuli (such as light touch or temperature changes); shooting, lightening, or electric shock–like pains; tingling, pins-and-needles, stinging, numbness, or burning pain; sense of painful abdominal or bladder bloating and burning sensations in the bladder.

Central pain syndrome can be divided into two categories: pain related to prior spinal cord injury and pain related to prior brain injury. Spinal cord–related pain occurs primarily after traumatic injury, usually due to motor vehicle accidents. Other reasons for spinal cord–related pain include complications of surgery, tumors, congenital disorders (conditions present at birth), blood vessel–related injury (such as after a spinal cord infarction or stroke), and inflammatory conditions involving the spinal cord. Brain-related central pain usually follows a stroke, although tumors and infection may also lead to brain-related central pain.

Demographics

Eight percent of all stroke patients will experience central pain syndrome; 5% will experience moderate to severe pain. The risk of developing central pain syndrome is higher in older stroke patients, striking about 11% of patients over the age of 80. Spinal cord–related pain occurs in a very high percentage; research suggests a range of 25-85% of all individuals with spinal cord injuries will experience central pain syndrome.

Causes and symptoms

In general, central pain syndrome is thought to occur either because the transmission of pain signals in the nerve tracts of the spinal cord is faulty, or because the brain isn't processing pain signals properly. Although details regarding the origin of central pain syndrome remain cloudy, some of the mechanisms that may contribute to its development include muscle spasm; spasticity of muscles (chronically increased muscle tone); instability of the vertebral column (due to vertebral fracture or damage to ligaments); compression of nerve roots; the development of a fluid-filled area of the spinal cord (called a syringomyelia ), which puts pressure on exiting nerves; and overuse syndrome (muscles that are used to compensate for those that no longer function normally are over-worked, resulting in muscle strain).

The pain of central pain syndrome can begin within days of the causative insult, or it can be delayed for years (particularly in stroke patients). While the specific symptoms of central pain syndrome may vary over time, the presence of some set of symptoms is essentially continuous once they begin. The pain is usually moderate to severe in nature and can be very debilitating. Symptoms may be made worse by a number of conditions, such as temperature change (especially exposure to cold), touching the painful area, movement, and emotions or stress. The pain is often difficult to describe.

Diagnosis

Diagnosis is usually based on the knowledge of a prior spinal cord or brain injury, coupled with the development of a chronic pain syndrome. Efforts to delineate the cause of the pain may lead to neuroimaging (CT and MRI scanning) of the brain, spinal cord, or the painful anatomical area (abdomen, limbs); electromyographic and nerve conduction studies may also be performed. In many cases of central pain syndrome, no clear-cut area of pathology will be uncovered, despite diagnostic testing. In fact, this is one of the frustrating and confounding characteristics of central pain syndrome; the inability to actually delineate an anatomical location responsible for generating the pain, which creates difficulty in addressing the pain.

Treatment team

Neurologists will usually be the mainstay for treating central pain syndrome. Physical and occupational therapists may help an individual facing central pain syndrome obtain maximal relief and regain optimal functioning. Psychiatrists or psychologists may be helpful for supportive psychotherapy, particularly in patients who develop depression related to their chronic pain.

Treatment

A variety of medications may be used to treat central pain syndrome. Injection of IV lidocaine can significantly improve some aspects of central pain syndrome, but the need for intravenous access makes its chronic use relatively impractical. Tricyclic antidepressants (such as nortriptyline or amitriptyline) and antiepileptic drugs (such as lamotrigine , carbamazepine , gabapentin , topiramate ) have often been used for neurogenic pain syndromes (pain due to abnormalities in the nervous system), and may be helpful to sufferers of central pain syndrome. When muscle spasms or spasticity are part of the central pain syndrome, a variety of medications may be helpful, including baclofen, tizanidine, benzodiazepines , and dantrolene sodium. In some cases, instilling medications (such as baclofen) directly into the cerebrospinal fluid around the spinal cord may improve spasms and spasticity. Newer therapy with injections of botulinum toxin may help relax painfully spastic muscles. Chronically spastic, painful muscles may also be treated surgically, by cutting through tendons (tendonotomy).

Severe, intractable pain may be treated by severing causative nerves or even severing certain nervous connections within the spinal cord. However, while this seems to provide pain relief in the short run, over time, about 60-80% of patients develop the pain again.

Counterstimulation uses electrodes implanted via needles in the spinal cord or specific nerves. These electrodes stimulate the area with electric pulses in an effort to cause a phenomenon referred to as "counter-irritation," which seems to interrupt the transmission of painful impulses. Deep brain stimulation requires the surgical implanatation of an electrode deep in the brain. A pulse generator that sends electricity to the electrode is implanted in the patient's chest, and a magnet passed over the pulse generator by the patient activates the brain electrode, stimulating the thalamic area.

Prognosis

Although central pain syndrome is never fatal, it can have serious consequences for an individual's level of functioning. Severe, chronic pain can be very disabling and have serious psychological consequences. Furthermore, central pain syndrome remains difficult to completely resolve; treatments may provide relief, but rarely provide complete cessation of pain.

Resources

BOOKS

Braunwald, Eugene, et al., eds. Harrison's Principles of Internal Medicine. NY: McGraw-Hill Professional, 2001.

Frontera, Walter R., ed. Essentials of Physical Medicine and Rehabilitation, 1st ed. Philadelphia: Hanley and Belfus, 2002.

Goldman, Lee, et al., eds. Cecil Textbook of Internal Medicine. Philadelphia: W. B. Saunders Company, 2000.

PERIODICALS

Nicholson, Bruce D. "Evaluation and treatment of central pain syndromes." Neurology 62, no. 5 (March 2004): 30–36.

WEBSITES

National Institute of Neurological Disorders and Stroke (NINDS). Central Pain Syndrome Fact Sheet. <http://disabilityexchange.org/upload/files/150_Central_Pain_Syndrome.doc>.

ORGANIZATIONS

American Chronic Pain Association (ACPA). P.O. Box 850, Rocklin, CA 95677-0850. 916-632-0922 or 800-533-3231; Fax: 916-632-3208. ACPA@pacbell.net. <http://www.theacpa.org>.

American Pain Foundation. 201 North Charles Street Suite 710, Baltimore, MD 21201-4111. 410-783-7292 or 888-615-PAIN (7246); Fax: 410-385-1832. info@pain foundation.org. <http://www.painfoundation.org>.

National Foundation for the Treatment of Pain. P.O. Box 70045, Houston, TX 77270. 713-862-9332 or 800-533-3231; Fax: 713-862-9346. markgordon@paincare.org. <http://www.paincare.org>.

Rosalyn Carson-Dewitt, MD