CENTRAL PAIN

Central pain is due to permanent neuronal changes in the spinal cord or brain.

Longstanding pain can cause permanent changes in cortical neurons. In patients with chronic pain, electrical stimulation of large areas of the cortex that normally have nothing to do with pain, can reproduce the same pain.

Longstanding pain may set up a memorized pattern for pain, possibly in the thalamus. (One patient continued to experience the pain of an ingrowing toenail after a traumatic cord transection.)

Damage to the spinal cord may remove spinal inhibition of a pain pattern. (A cordotomy for cancer pain resulted in one patient re-experiencing the severe pain of a patella fractured six years earlier.)

Treatment of central pain can be with psychotropic or membrane-stabilizing drugs, but a combination of a tricyclic and a phenothiazine is probably the most helpful. (see Nerve Pain)

Mr. B. C., a 37 year old with a thoracic glioma, became paraplegic. He then started to complain of severe sacral pain. After several months of pain he underwent a therapeutic spinal cord transection which failed to control the pain. The pain fluctuated in severity but was constant, worse on sitting up, and disturbed his sleep. It was overwhelming at times, so that he was unable to think of anything other than his pain. 5mg, 10mg and 20mg of morphine every 4 hours caused increasing drowsiness, but did not affect the pain. NSAIDs had no effect. X-rays of the sacral area were normal. The pain was eventually well controlled for the last two months of his life by a combination of chlorpromazine 75mg 4 times a day, and imipramine 100mg at bedtime, which caused virtually no drowsiness. This severe pain can only be explained on the basis of a central mechanism. (see Pain Pathways)

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