Traditionally, it is held that touch is carried in the posterior spinal tracts, also known as the Dorsal Columns. In this designation are the fasciculus cuneatus (arms upper body) and the fasciculus gracilis (legs lower body)
However, it must be remembered that much of the anatomical work has been done in monkeys or apes. Assumptions have been made, but we are not certain about humans.
Touch and painful touch do not always go together. For example, touch on the face goes directly to the medulla, while pain from the face drops down to the cord with the descending tract of the trigeminal nerve, to join a tract, the substantia gelatinosa which is carrying pain from the body. This is why some with Central Pain from cervical lesions may burn severely on the face, mouth, and nose (occasionally the eyes as well)..
Is your examiner really able to assess your superficial sensory neurologic status? It is difficult and unless he is using von Frey hairs (light filaments which detect subtle sensory loss) you are not really being tested. The safety pin is WAY too much stimulus for testing superfical sensitivity loss and the patient may come off the table with a pin prick, due to the hyperalgesia which characterizes Central Pain with incomplete lesions.
Temperature sensation is tested in Europe but almost never in the United States. Managed care administrators are not likely to approve such time consuming efforts, since the room, the patients skin and the testing electrode (or test tube) must be brought to a standard temperature before evaluating for decreased sensitivity to temperature. Furthermore the patient, who suffers the agony of the damned in cold water or cold temperature blasts will wrongly assure the doctor that they have excellent temperature discrimination..
Touch itself has been subdivided and LIGHT touch is thought to be carried in the front of the cord, to the side, in the anterior spinothalmic tract (goes from the spine to the thalamus, at the center of the brain back from the eyes. No one is certain what touch is carried in the lateral spinothalamic tract, but monkeys have this so humans are assumed also to carry some particular sensation in the LST tract. Pain is also subdivided. For example, burning pain is thought to be carried in the spinoreticular tract, while ordinary pain is carried in the spinothalamic tract. These tracts go to both the thalamus and the subthalamic nucleus. Pain from the muscle spindles (contraction pain) is carried in the before described dorsal columns, it is thought.
So the question arises, “What is the pathway of pain coming up to the brain in those with transection of the spinal cord?” Theory from people such as Schott is that pain nerves travel with blood vessels and may reach the brain this way in those with interruption of the spinal cord. The point is that some selection and filtering of pain is going on even before it gets to the brain. Consequently, one wonders precisely which tract or tracts carry the burning dysesthesia which so torments the Central Pain patient. It is possibly the anterior spinothalamic tract, which also carries light touch. The lancinating or lightning pains are carried in the posterior columns, it is thought.
In 1949 experiments by Hardy showed that if a tourniquet is placed on the arm, pain disappears in increments. So called quantum pain means that one type of pain disappears, and then another, until the very last pain to go is a burning, which has little or no discriminative information, which is called protopathic pain. it is assumed that Central Pain is in fact protopathic pain, as the descriptions are very siimilar. If this is correct, the brain is operating on very little information and may be tgurning the recpetion end of things up, up, up producing the agony of Central Pain. When fully elaborated, the subject cannot tolerate the touch of clothing. Blasts of cold air are intolerable.
In the normal person, pain is felt as an aggregate of inputs. The patient knows if the pain is sharp or dull, hot or cold, diffuse or localized, and the location of the pain is typicaly known. These features are not so apparent in Central Pain, or perhaps not apparent at all. Nonlocalizing pain is not a familiar concept to most doctors, let alone the public, causing many communication problems.
The agony which is felt may be poorly localized, and temperature reversal may cause cold air ot result in a burn. In other words, those features medical students learn to ask about pain are missing in Central Pain. This causes not a few to doubt that the patient has pain, since even poor historians tend to be laser accurate about pain.
Central Pain patients should attempt to think about their pain sensations so they can educate their doctors Since most spine injured people have had surgeries, the CP subject will usually have ordinary pain from alteration of the motion segments of the spine This pain may respond to opiates, while the burning dysesthesi usually does not. Wall reported “Brain” that those with bright lesions on MRI tend to have NO pain, while those with no unusual signal on MRI are the ones which most typically develop central pain. This is consistent with the size of the tracts in the spine, since the ST tract is not a discrete tract, bur rather like telephone wire, a bundle which in total is less than 0.5 mm, which is below the resolution of existing MRI. The other tracts mentioned above are even smaller.
All of this may combine to make the examiner skeptical, the inabilty to describe abnormal pain, the normal MRI, the bizarre things which evoke the pains. If patients will concentrate, and then communicate with the doctor, it may be possible to gain understanding by the medical profession of what is going on. This will save a great deal of wasted time, expense, and accusation of malingering or drug seeking. We hope doctors will realize that much of what they learned in medical school did not cover what is necessary to understand Central Pain.