I wrote earlier that the feeling of pain is produced in the brain after it processes nerve signals from the rest of the body. Interestingly, the brain itself has no pain receptors. Cutting the brain during surgery in awake patients does not hurt them although cutting the scalp does.

However, if certain parts of the brain are damaged by a stroke (in stroke, brain cells die) intractable pain that resists treatment can sometimes occur. Phantom limb pain is now known to be the result of changes in the brain triggered by the loss of nerve signals from the amputated limb. In fibromyalgia, a condition characterized by generalized musculoskeletal pain, research has discovered objective abnormalities in the brains of affected individuals.

In these examples what seems to happen is that the brain mechanisms responsible for the feeling of pain have been disrupted in some way. This breakdown in function is responsible for the pain that is felt. One idea percolating through the literature is that trauma to any part of the body can set off a chain reaction in the nervous system that leads to changes in the brain and/or nerves. These changes result in pain, sometimes in a different location from the site of the original trauma. Gunshot wounds to the shoulder often lead to intense burning in the hand, a form of nerve pain.

One name for this chain reaction is central nervous system sensitization. In all of the above painful conditions, those affected have abnormal sensations and often extreme sensitivity to being touched in the area that hurts. Even the lightest pressure may produce pain.

Given the above, just as rheumatoid arthritis is a disease caused by inflammation of the joints, at least some pain can be a disease caused by abnormal nervous system function. This may apply to conditions other than those mentioned here – an idea I will explore further.