The Muscle Problem in Central Pain

Although perhaps the least spoken of, the muscle problem is certainly not a minor factor in the Central Pains. You will find yourself in the paragraphs of this article depending on the degree to which you possess garden variety spasticity, as well as “CP spasticity”, the latter including some false sensations, as described below.

This topic is difficult to address simply because any discussion is rooted on anatomical understanding which most do not possess. Also a problem is that for the paralyzed, to complain about pain with movement seems self indulgent. In some degree it is, but if the completely paralyzed understood the pain associated with the movement they would clearly recognize the mixed blessing, with pain so severe that movement may not seem like a blessing at all. “Muscle and Nerve” had an article reporting on CP patients for whom the pain of movement was so great that they were functionally paralyzed even though they had an intact motor unit.

Oddly, some patients have ONLY muscle pains as their Central Pain and are not aware that most others have burning dysesthesia of the skin. Pain is carried both in the anterior cord (spinothalamic tract or ST pain) and in the posterior cord (lemniscal pain). Those with pain carried in the posterior cord are the most likely to have muscle pains and are also likely to have prolonged latency on the SSEP, or somatosensory evoked potential testing. Posterior cord CP should be aggressively pursued, since it is often treatable by medications, including with conventional pain medicines. ST pain is usually not treatable to any major degree.

At the center of the problem of discussing CP motor pain is the difference between problems of spasticity and the difference between kinesthetic dysesthesia and isometric dysesthesia.

Spasticity can be truly terrible for the spinal cord injured. Patients often discover things which tend to set off episodes of violent spasticity. These may include anything from transfers from wheelchair to bed, sex, or prolonged laying in one position. Other inciters include attention garnering activity from the environment, such as being moved, spoken to, or approached. It is important to realize that spasticity, as such, is NOT central pain. It is due to injury in the inhibitory tracts coming down to the anterior horn of the cord, where muscle activity is centered neurologically. Without inhibition, impulses may set off wild movement, some of which even result in fractures. The same thing is seen in epileptic grand mal seizures, although the mechanism is different. The tracts are intact to the cord in epilepsy, they merely lose control from the brain cortex when waves of concentrated firing take over the brain momentarily.

Many or most with SCI central pain have some spasticity, but they may not recognize it as such. Even in those who are mobile, if they have the lancinating pains, they also generally have some form of micro-fasciculations. These are tiny discharges in the muscles so that there is slight movement. It combines with the injuries leading to true spasticity so it is difficult to separate them. Manifestations include inability to hold the muscles in one place, such as attemping to hold perfectly still for an MRI, or holding the jaws clenched to hold the little carrier which contains dental xray film in the mouth.

Such patients nearly always have a positive Hoffman sign. This is a physical sign of uppper motor neuron injury, and its frequent presence in all SCI makes it even harder to say that this is part of central pain rather than minor spasticity of the garden variety. When it is associated with lancinating or shooting electric pains, we feel that it is in fact neuropathic. Most clinicians perform the Hoffman test incorrectly and consequently miss it most of the time in SCI which is sensory rather than motor. The common way to perform a Hoffman test is to compress the nail of the middle finger and let go suddenly. In the really severe motor spastic, the index finger will drop downward toward the thumb in an unconventional fashion.

This is a very insensitive way to test and picks up only those who are so obviously spastic that the Hoffman’s test need not really be done. Hyperreflexia at the kneecap or the elbow is usually more than sufficient. Much more sensitive is to support the patient’s left wrist with the fingers hanging downward. Using the middle finger of the doctor’s right hand, the examiner flicks the patient’s left middle finger upward quite briskly (the procedure is reversed to test the opposite side of the body). This flicking will also cause the patient’s index finger to move downward toward the thumb, perhaps three quarters of an inch, and then back upward, over about a half second’s time, in a sort of motorized or reflex manner. In a normal person, the index finger will NOT move downward. Inhibition in the upper motor neurons has been diminished.

Although it is actually a test of minor conventional spasticity, it is interesting how many who have a positive Hoffman’s sign also have the lancinating pains of CP. We have spoken elsewhere about the mysterious links between the motor and sensory systems and do not apologize for being unable to explain the precise anatomical links which make Hoffman’s sign tend to be associated with lancinating CP pain.

Also significant, is that while the patient with lancinating CP frequently can sense unceasing, completely random
“muscle fasciculations” in the distal extremities, these are NOT visible. Such a patient may indeed have visible contractions, which would be fasciculations by anyone’s terminology, but these are infrequent, with perhaps months between episodes. The micro-fasciculation are constant and the patient can perceive them ALL the time if he/she concentrates. Not infrequently, if the patient is already paying attention, a microfasciculation in a certain spot, about the size of a nickel perhaps, will occur at the same time as the generation of a lancinating jolt which shoots TOWARD the brain. It is not clear whether these are actual fasciculations or mini-contractions. As far as we are aware, no one has yet managed to catch one of these on an EMG test.

One of the hallmarks of Central Pain is pseudocramp, or the perception of a severe cramp where none exists. This perception may be only a sense of tightening, such as in Multiple Sclerosis, where the tightening has a nickname, “MS Hug”. Some earlier authors described this as pseudo-claudication, after the acheing patients with severe venous insufficiency feel in the lower legs. However, in Central Pain, the pseudocramp need not be in the lower leg. The MS Hug is noticed as different, but not necessary frightening, whereas the lancinating jolt is often jolting when it occurs, often bearing a similarity to a stab or severe sting. Generally, however, the tightening, drawing, tearing or whatever muscle action is signalled by CP is much more noticeable than a hug, and usually described as cramplike or “drawing rightening”. Similar to the way pins and needles in central pain can nearly drive a patient crazy with their nonstop incessant tingling, the persistent cramp can cause strong emotional distress. Any noxious stimulus, or for that matter, any non-obnoxious sensation whose annoyance is neverending can cause anger or other strong emotion. The brain needs its peace and quiet to “think”.

There is a mysterious “withdrawal reflex” in some with cord injury and CP. Dr. Hammer, author of DeJong’s The Neurologic Examination is of the opinion that this is due to unmasking of primitive spinal protective reflexes, which are best observed and differentiated by studying stages of fetal spinal cord development in lab animals or in newborns. This withdrawal results from unexpectedly being touched or inadvertently touching something and occurs ONLY when the patient is NOT aware they are going to be touched. The extremity or hand withdraws from where it is touched in a brief rhythmic, characteristically reflex, spastic manner. This can result in injury, such as when the skln of the forehead unconsciously touches the rim of the car door molding and on rebound the back of the head hits the actual open door behind the head with force. This is when the CP subject feels like a “gimp” and is demoralized. They cannot keep from hurting themselves.

The delayed form of kinesthetic dysesthesia is simply a profound soreness that occurs hours after activity, an exaggeration of overdone muscle activity such as any person might feel, but to an extreme degree. “Lactic acid buildup hypersensitivity” it has been called. It is not surprising in a nervous system which is so HYPERSENSITIZED (hypersensitized sounds like such a weak word compared to the agony, but it refers to processes like sunburn which can hypesensitize the skin). It has been compared to someone who has not exercised all year who impulsively decides to enter a full marathon. Their soreness the next day includes not only reluctance to move, but outcries if anyone pushes into their muscles.

The muscle pains of Central Pain may be divided into three categories. The first is kinesthetic dysesthesia, which has both a short term and a long term component. “Kinesthetic” means “related to movement”.

The SHORT TERM kinesthesia refers to the pain engendered by movement, or when the muscle is put under a load, such as assuming a squatting position. This pain generally has a component of burning which is not identical to skin dysesthesia, but close enough to be recognized as central pain, ie dysesthetic.

The LONG TERM kinesthetic dysesthesia is a profound soreness, not so clearly dysesthetic, which occurs AFTER some activity. The CP person who can walk may pay the price after a few hours. The soreness may extend into the next day. The progressive disincentive to move leads to atrophy, weakness, and further disability. Unfortunately, this aspect of CP is virtually unknown even in the medical profession and prevents insurance coverage for needed physical therapy, which may have to be lifelong and more or less daily.

“Isometric” refers to stationary voluntary contraction or taking on a muscle load without movement, or deliberate tightening of a muscle. In Central Pain, this sensation is most likely to follow periods of inactivity, such as on awakening, or after sitting in a chair for a time. They have been called “confinement cramps”. They are similar to someone who has been placed in the back seat of a car which has insufficient room and must remain in that position all day. The soreness is not particularly dysesthetic, but can be severe and destroy the incentive to move, where it is neurologically possible to do so, even to a slight degree, as in partial or incomplete cord injury. ANY person feels crampy after being in one position too long, but in the HYPERSENSITIZED state of Central Pain the sensastion is much more dramatic and demoralizing.

BOTH kinesthetic and isometric muscle pains respond to stretching of the muscle belly or tendons. This usually needs to be very heavy stretching to quiet the muscle spindles. Because the pain fibers in the tendons are part of the gamma motor system, or muscle spindles embedded in muscle fibers, this pain has been called “gamma pain”. The pressure must often be heavy to the point of having someone stand stationary on the patient’s legs. It is important to remember that veins in the legs have little hammocks, or backward flow impeding valves, attached at three points, inside the vessel wall to keep blood from flowing back downward into the limb. Standing on the legs can rupture these valves, blowing up varicose veins in the legs.

Consequently, attempts at therapy should include the heavy pressure but should be done in progressive application of the pressure so as to move blood toward the heart and not to create incompetent, ruptured, veinous valves, which produces varicose veins. Since CP patients must often go mostly unclothed to avoid the pain of light touch, the presence of large varicosities makes the exposure more embarassing.

A fair number of those answering the survey have a constant, really severe sensation of cramp somewhere in the body, and this is not particularly likely to be located in the area of skin dysesthesia. For example, the patient may have a nearly unbearable cramp behind the right thigh all the time, but the burning may be down on the ankles and feet bilaterally. Inexplicably, while such medicines as clonazepam, a muscle relaxant, may reduce skin burning, they do not have an impressive or perhaps ANY affect on this perception of heavy cramp. The reason is unknown. Only physical therapy seems to help it and the relief is very brief, often lasting for less than a day.

This reviews some of the muscle problems in Central Pain. We do not yet know the neuro-anatomic substrate of these sensations, but the relief of Central Pain from open motor cortex stimulation suggests there is still much to be learned about ties between the muscle and sensory cortex in the brain.

It is our opinion that many of these matters could be addressed by targeted physical therapy, but such matters do not constitute the training of most therapists and so the condition is likely to continue to be ignored until third party payers recognize that no one needs PT more than those with SENSORY CP. The conventional wisdom is that the role of PT is to get the muscles working and build strength, not to relieve pseudocramp, or kinesthetic and isometric dysesthesia.

Claire Hulsebosch at UTMB has documented the reluctance to movement of CP rats and has also shown that gabapentin diminishes this problem. Kinesthetic and isometric dysesthesia have significant implications as to the disability of those with incomplete motor injury from SCI, who also have Central Pain. Even the totally paralyzed may have pain in the muscles. We suspect stretching the muscle tendons is also important for them but lack sufficient data to make the claim. The area has been much neglected in CP studies and a more careful history should be obtained from every CP patient. Many with minor fasciculations do not mention them because they may not be nearly so severe as the skin dysesthesia. MOST or

nearly all of the fasciculations do NOT generate a lancinating pain, and some may only be aware of a fasciculation generating a lancinating event if they pay very close attention, or are coached to do so. Even so, the fasciculation may be so minor and the shooting pain so severe that there may be no perception of a fasciculation. Better attempts at histories will provide more information and more rational therapies,tailored to the individual. Physical therapy is not going to help the burning skin dysesthesia which may make conventional PT massage unbearable, but PT may be just the thing for posterior column pain so long as the skin is merely compressed and NOT rubbed.

If any of you have any muscle pains related to your CP which have not been covered here, PLEASE report them in the comment box below this article. Include what makes the muscle pain worse and what makes it better.

Neuroscientists are a bit mystified when to refer to something as central sensitization and when to call it Central Pain. For example, those with irritable bowel syndrome display some of the same chemical changes at nerve synapses as do those with Central Pain. This does not detract in any way from the reality of Central Pain. Instead, the occurrence of minor versions of nerve dysfunction should give solid verification of the existence of a fully developed, mother of all pain states where EVERY sensation may be hypersensitized, ie. Central Pain. For naming, the clinician should think of Central Pain as secondary to INJURY to the CENTRAL nervous system. CP shares MANY characteristics with peripheral hypersensitization, particularly in how the synapses can get worked up into a pain frenzy, which has the polite name of “hypersensitization”. We have not met anyone with CP who is likely to say, “I say, today I feel a bit hyper in the pain system”. However, if this is the best word the scientists can come up with, we will have to live with it, although the word makes us laugh. It would be like inmates at Auschwitz saying, “You know, today I think I have been the victim of discrimination.”

At any rate, hypersensitization of any kind bears witness to the possibility that hypersensitization just might be capable of being a tsunami of pain chemicals. However, they will be likely to be many of the same chemicals. How could it be any other way. The body would not be likely to have two entirely separate ways for synapses to gear up chemically. If a car takes gas to go thirty miles per hour, it just takes MORE gas to go 120 mph. If a moderate amount of NMDA, glutamate, pERK, etc will cause central sensitization, what will a flood of it do? It would appear that CP patients are so genetically messed up they also produce ion channels to receive these devil pain chemicals, but even that may eventually be shown in some cases of central sensitization.

There are many steps in the chemical cascade of pain. Volumes could be written about only the changes in how calcium is handled. Just as there are 13 steps in the cascade of blood clotting chemicals, any one of which can affect clotting, there are many steps in the pain cascade. We suspect CP patients have more than their share of abnormalities. So far, lab rats with severe CP seem to have ALL of them. Severe Central Pain subjects are Pain Kings and Queens, in the “dumb and dumber” kind of rating. We are not in the least surprised that there are many lesser versions of nerve injury pain and we of all people do not denigrate or diminish the severity of such states. Who knows better the suffering they endure than ourselves, who are the MOST likely to be compassionate to their condition. We also consider that society should aid them in their plight and that they will be able to to survive their pain. About ourselves, we are not so sure.

Pain does not just have its talons in us, it has more or less confiscated us. Having take big chunks out when we were first facing it, CP then defaults into an attrition mode. Day by day, severe pain pilfers our lives and identity until we are left wondering who and what we have become.