Injuries of Nerves and their Consequences
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- In contrast to ordinary pain, which tends to be worse in the evening, the person with nerve injury pain awakes with it and it "pursues him with increasing torture throughout the day" Weir was contrasting it with toothache pain, which doesn't get going until there has been time for circulation to occur during the day.
- The "remote" cause of nerve injury pain is in the wound, while the "immediate" cause is in the site of origin of the nerve; a very astute observation and ahead of Dr. Mitchell's time. Spontaneous and evoked pain would be consistent with this theoretical arrangement wherein immediate causation results in spontaneous continuous pain while stimulation of an area of the body elicits greater pain as the "remote" augmenting location.
- In most gunshot wounds when chronic nerve injury pain appears, it is usually a burning pain, while at the time of direct physical injury to a nerve, other forms of pain are to be found. Discussing this, Mitchell gave his famous quote, "Under such torments the temper changes, the most amiable grow irritable, the soldier becomes a coward, and the strongest man is scarcely less nervous than the most hysterical girl" (Injuries of Nerves, p 196)
- The burning almost always arises during the healing of the wound and is described as burning, mustard red hot, or like a red hot file rasping the skin". (typical, garden variety, description for what today is called "dysesthesia")
- The most pronounced site of the burning pain is "the hand and foot" (this is the distal gradient also described by Roussy), where the dysesthesia is most severe on the palm of the hand and the top of the foot. The compromise in sensation is greatest where the causalgia, or burning pain, is greatest (This pattern is consistent with that related by central pain patients today).
- Cold weather usually eased the pain while heat made it worse. (This again is typical of Central Pain to a point, since it is really changes in temperature which begin the sensitization-its completion can occur at either temperature extreme. In ciguatera poisoning, the change of cold to a hot burning has been called "cold reversal".
- The burning is not a referred sensation since division of nerves going to the area did not stop the pain. (Once again, Mitchell astutely realized that it was not the nerves themselves causing the pain but something else. Today we would point to the fact Central Pain comes from the brain due to chemical impact of altered genes in the spinal cord neurons, and that evocation occurs with input from kinins, prostonoids, and the similar sensitizing chemicals near the area of applied stimulus.)
- The pain from injury to peripheral nerves occurs immediately when the skin is touched while evoked nerve pain injury in the central nervous system (Central Pain) is delayed from the time of the touch. (We speak of "temporal summation" of dysesthesia today--Mitchell cites measurements by Cruvalhier with a watch indicating quarter seconds). This very important feature of Central Pain, the delay from stimulus until onset of evoked dysesthesia is the major distinguishing characteristic of Central neuropathic pain from Peripheral Neuropathic pain and a an extremely useful clinical test for differentiation of central versus peripheral neuropathy. This should quite possibly be called "Mitchell's Sign", since he was the first to describe it. (Injuries of Nerves p.225)
- A contusion (bruise) is more likely to give rise to more serious injury than direct mechanical injury to the nerve, with "bruised" nerves more likely to pass into chronic pain than a direct wounding of the nerve (i.e. Central pain is an intermediate injury and requires some level of functioning for it to be generated).
- Injured nerves sometimes displayed centrally progressive deterioration. (This brings to mind the modern phrase from Patrick Wall, "Peripheral injury induces central change.")
Injured nerves sometimes give rise to fibrillar spasms and cramps occur for no particular reason. Weir Mitchell found this reminiscent of the phenomenon in healthy nerves wherein nerves which have been cooled by icing, when tapped, send muscles into sudden spasm. (Recent FMRI studies have shown the cerebellum tends to keep muscles on alert, possibly an abnormal variety of "being on alert" for escape from pain).
It is not possible to explain why an identical injury will sometimes reach the cerebrum and sometimes not.
Dr. Pijusas from Visciakaimis