Why Does Complex Regional Pain Syndrome Occur?
The origin of CRPS is theorized but still not fully understood. To know what changes could happen to induce CRPS, knowledge of the nervous system is necessary.
There are two different types of nervous systems in the body. The more primitive one is the autonomic nervous system. The somatic nervous system (soma means body) is the other type.
These two systems have different responsibilities. The autonomic nervous system is the “housekeeping” system. The somatic nervous system is the conscious system. This somatic system is the one that delivers signals to and from the brain that we can “feel” and control. Motion of our body occurs through this somatic system.
The autonomic system plays a major role in complex regional pain syndrome.
The Autonomic System
The autonomic system consists of two parts, the sympathetic nervous system and the parasympathetic system. You might remember the sympathetic system from high school as the “fight or flight” system. When a human is in danger, the heart pumps harder, the muscles engorge, adrenaline pumps into the bloodstream and vision becomes sharper. This is a direct result of stimulation of the sympathetic system.
The parasympathetic system is the system of maintenance of body functions. Digestion, relaxation and even sex are controlled by the parasympathetic system.
These two systems are generally in balance and both are needed to keep the body functioning. We have always thought these systems direct signals only one way (efferent). That is, they only send signals one way from the brain to the body but not the other way around (the body to the brain). We have found no sympathetic “sensory nerves”.
The sympathetic system is intimately connected to the arteries. Arteries obviously carry blood from the heart to the extremities. Veins of course carry blood back to the heart. Arteries have thick, muscular walls whereas veins have paper-thin walls. The arteries can contract since they are muscular lined. This contraction, which narrows these vessels, is controlled by the sympathetic nervous system.
This vessel wall contraction is important for survival. If we are out in a very cold environment, the blood vessels of the skin will contract to reduce blood flow and preserve heat. If we are engaged in strenuous physical exercise, the blood vessels open to allow more oxygen into the muscles to keep them functioning at a high level. If we lose too much blood, the vessel walls will contract to prevent shock from developing.
Sweating is also under control of the sympathetic nervous system. Sweat glands are directly wired to produce sweat under the influence of the sympathetic nervous system and adrenaline. Sweat occurs to allow cooling from evaporation to prevent the core from overheating.
Contraction of the blood vessels as stated before will restrict the blood flow. Since blood flow brings heated blood from the core to the extremities, contraction of these vessels will allow the extremity to become cooler. What is counterintuitive is that the loss of sympathetic nerve supply (called loss of sympathetic tone) will warm this extremity, as there is no restriction of the warm blood flow.
Complex regional pain syndrome has an initial warm stage and then only later does the extremity become cold. This warming is thought to be due to the initial loss of the sympathetic nerve supply to the injured part. This loss means the arteries will initially dilate and bring more warmth to the extremity.
Later in CRPS, the artery muscle cells “miss” the sympathetic nerve supply and up-regulate to become more sensitive to circulating catecholamines (adrenalin) in the blood. This adrenalin will cause these more sensitive cells to contract. This contraction slows blood flow, which causes the “coldness” of the involved extremity..
The CRPS “Mis-Direction” of Nerve Signals
CRPS is thought be related to a miscommunication between the sympathetic nerve fibers and local pain nerve fibers. Pain fibers, like sympathetic fibers follow blood vessels. It turns out that sympathetic nervous system fibers and pain fibers are both unmyelinated (not wrapped by myelin) small diameter fibers. This makes them somewhat compatible to cross-connect.
What might happen in
is that there is an accidental connection between the pain fibers and the sympathetic fibers. In turn, there is a disconnection between the sympathetics and the blood vessels.
If this abnormal connection occurs, it fits with the symptoms. The sympathetic fibers will send a signal and the message never gets to the muscular wall of the artery. Instead, the abnormal connection to the pain nerves inadvertently reroutes a pain signal to the brain. Since the sympathetic signal never gets to the extremity, the blood vessels cannot contract and the extremity initially becomes warm and swollen.
Complex Regional Pain Syndrome Symptoms
The overlying factor in CRPS is pain avoidance behavior patterns. The extremity is so unreasonably painful that the patient will avoid any contact with this area. This leads to disuse atrophy and the old saying “if you don’t use it, you lose it” is never truer than with this disorder. Disuse is suspected to cause a significant portion of the symptoms. The stages in complex regional pain syndrome generally have to do with the length of presence of this disorder.
Stage one occurs initially after the injury. This stage is noted by severe burning pain, swelling of the skin, stiffness of the involved joint and reduced range of motion. The skin turns reddened and swelling occurs. Some patients may note increased sweating of the involved part (hyperhidrosis).
Allodynia is typical in this stage. This is pain occurrence upon normal stimuli. A light touch will burn. If the patient is caught early in this stage, a physical therapist with experience in treating CRPS can be very helpful.
Stage two can be noted by more intense pain. The joint becomes more swollen and hair growth diminishes. The nails become atrophic (thickened and brittle). Disuse of the extremity occurs due to pain and osteoporosis (loss of bone mass) occurs. This is due to Wolfe’s law, which states that bone that is unloaded will lose bone stock. The arm notes disuse atrophy, as muscles are not used.
Stage three is the end stage for RSD. The muscles have not been used so the arm is atrophic. The joint involved will become contracted and useless. The pain causes the individual to ignore the extremity. Disuse osteoporosis is severe. Skin is shiny and smooth.
The goal is to avoid this stage by aggressive PT prior to onset of stage 3.
There is no single diagnostic test for CRPS. Diagnosis is a compilation of different findings based upon a thorough history, physical examination and possible imaging findings. The diagnostician needs to rule out other potential pain generators before the diagnosis of CRPS is considered. That is, a diagnosis of
is a diagnosis of exclusion.
Complex Regional Pain Syndrome Treatment
The mainstay for treatment is early occupational and physical therapy. Desensitizing the involved area is paramount. There are modalities that can be used including direct stimulation of the area, electrical stimulation, contrast baths, medications and even implantable stimulators and pumps.
For additional resources on complex regional pain syndrome (CRPS), or to determine if you are experiencing symptoms of