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Thigh / Knee / Leg / Ankle / Foot - Complex regional pain syndrome
RSD … few diagnoses strike greater fear into the hearts of physicians or deeper despair into the minds of patients than this does.

RSD (Reflex Sympathetic Dystrophy) is the former name for a “mysterious” chronic pain syndrome which is universally considered to be incurable by most doctors. Patients who develop RSD are told that “they must learn to live with pain,” and are then consigned to the realm of pain management for the rest of their lives.

In 1993, the International Association for the study of Pain (IASP) changed the terminology regarding RSD. Initially, they introduced the term Complex Regional Pain Syndrome (CRPS) and the two terms were used interchangeably for a while. Then, in 1994, the terminology was refined, adopting two new terms: CRPS type I (CRPS-I) and CRPS type II (CRPS-II).

CRPS-I became the new term for a condition which was formerly known by several names, but most commonly referred to as RSD. CRPS-II became the new term for a condition formerly known as “causalgia.” Despite attempting to clarify the language by adopting these new terms, many doctors, patients, and support groups still use the old nomenclature of RSD and causalgia to refer to CRPS-1 and CRPS-II, or mix up the terminology which can be a source of confusion.

The main difference between CRPS-I and CRPS-II is the confirmed presence of a peripheral nerve injury. In CRPS-I (RSD) there is no known or identifiable peripheral nerve injury. In CRPS-II (causalgia) doctors are able to identify injury to a specific peripheral nerve. Despite the fact that the IASP decided to change up the specific terms used to describe the problem, the medical community at large still has very little idea about what causes CRPS. It’s a little bit like rearranging the deck chairs on the Titanic.

Ironically, despite the symptoms and signs being virtually identical between CRPS-I and CRPS-II, few people have stopped to ask themselves if there is really any difference between the two entities. If a patient with an identified peripheral nerve injury (CRPS-II) and a patient with no identifiable peripheral nerve injury (CRPS-I) present with the same symptoms and signs, it raises the question as to whether or not these two conditions are a distinction without a difference. Theories as to the cause of CRPS range from autoimmune causes to an inappropriate inflammatory reaction to dysfunctional interaction between the central and peripheral nervous system. In summary, the question regarding the cause of CRPS is long on theories but short on consensus.

So what causes CRPS? When a peripheral nerve is injured, a pain signal is sent to the brain. At the level of the spinal cord, a reflex arc occurs where a sympathetic motor response is sent back to the area of the injured nerve. The chemical neurotransmitter involved in this process is called norepinephrine (noradrenaline) which is also responsible for the body’s “fight or flight” response. It is norepinephrine which produces the sympathetic responses seen in CRPS such as constriction of blood vessels, skin sweating, and erect hair follicles. With prolonged exposure, norepinephrine also acts as a nociceptive stimulus affecting pain fibers in adjacent normal nerves. This can result in the appearance of “spreading” of what was initially a localized phenomenon to a more regional problem affecting an entire arm or leg.

While doctors who regularly treat patients with CRPS understand that it is important to treat the condition early, they tend to focus on controlling the visible manifestations of the disease, the sympathetic motor responses – sweating, color changes, skin changes, etc. This is done with steroid injections targeting the sympathetic nerves at the level of the spinal cord. What they uniformly fail to appreciate is the importance of addressing the underlying peripheral nerve injury. This approach is like trying to put out a fire by sucking up all the smoke rather than dousing the flame.

It is a well documented fact that more than 90% of CRPS is triggered by a clear history of trauma or injury to the affected limb. It is also accepted wisdom among doctors who treat CRPS that 90% of CRPS patients fall into the CRPS-I category. Now remember that there is virtually no difference between a patient with CRPS-I and a patient with CRPS-II, other than the fact that doctors have been unable to identify a specific peripheral nerve injury in the CRPS-I group. This sets up a bit of a math problem. If 90% of all CRPS is triggered after a trauma to an arm or a leg, such as a crush injury, fracture, amputation, etc., but only a small percentage (~ 10%) of CRPS patients end up with an identified peripheral nerve injury (CRPS-II), it’s fair to ask the question: “How good are doctors at identifying peripheral nerve injuries to begin with?”

From a peripheral nerve standpoint, crush injuries, breaking bones, or amputating an arm or leg are about as good a mechanism as exists for causing injuries to peripheral nerves.
It turns out that doctors are really horrible at identifying underlying peripheral nerve injuries in the setting of CRPS. This is primarily due to the fact that the vast majority of doctors, especially the ones treating CRPS patients, tend to be very ignorant with respect to peripheral nerve anatomy. Additionally, they really have no idea how to properly examine the peripheral nervous system which is another critical factor in being able to pinpoint peripheral nerve injuries. When you understand this, it starts to make a lot more sense that even though more than 90% of CRPS patients sustain classic trauma mechanisms for injuring peripheral nerves to the affected arm or leg, only about 10% of CRPS patients are given the diagnosis of CRPS-II.

In reality, both studies and common sense tell us that most patients who are given the diagnosis of CRPS-I are really just incorrectly diagnosed CRPS-II patients. In other words, most CRPS-I patients are really CRPS-II patients. Unfortunately, many doctors making the diagnoses lack the training necessary to discern the location of the underlying peripheral nerve injury. This is the great secret as to why CRPS-I and CRPS-II patients both present with the same symptoms and signs – in most cases, they are suffering from the exact same underlying problem!!!
So why is this important? The reason this is important goes back to the original problem in CRPS with the smoke/fire analogy. It’s the underlying peripheral nerve injury (the fire) that produces the visible sympathetic motor reflex manifestations (the smoke) that everyone treating CRPS fixates on. The current system spends its efforts focusing on the smoke rather than the fire when it should be the other way around. Although treating the symptoms related to the sympathetic response is helpful, it rarely ever results in a cure for the patient. In order to really eradicate the problem, it is imperative to put out the fire! In other words, until you locate and deal with the underlying peripheral nerve injury, thereby shutting off the constant pain signal to the brain, it is very difficult to break the cycle and allow the patient be freed from the prison of pain!

In short, most cases of CRPS-I are really CRPS-II with a readily identifiable peripheral nerve injury (or injuries). These underlying nerve injuries usually take the form of nerve compression or sometimes neuromas, typically of smaller, relatively unimportant cutaneous (skin) nerves. The good news is that once the underlying peripheral nerve injuries are identified, appropriate surgical measures can be used to decompress pinched nerves or disconnect or reconstruct damaged nerves. This approach is very successful for resolving the horrible pain of CRPS and restoring the patient to a more normal quality of life.

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