RSD - Sympathetic Dystrophies and Mysteries
Dr J C D Wells MB ChB LRCP MRCS LMCC FRCA
All of us are aware of a syndrome that is seen in clinical practice. A patient with a minor injury, for example, a sprain or a Colles fracture, or one who has had some simple and uneventful surgical procedure, goes on to have pain and sensitivity to light touch which is disproportionate to the event. The pain is often intense. It may develop immediately, or gradually escalate over a number of months. Function is reduced. Often, emotional distress ensues.
As time goes on, secondary changes can be seen; swelling or oedema. Changes in skin blood flow, often initially an increase and redness of the skin, give way to a decreased skin blood flow with pallor and coldness of the affected limb (because it is almost always the limb or the face. It does not occur in the trunk). There may be abnormal pseudo-motor activity (sweating).
This condition used to be called a reflex sympathetic dystrophy, and indeed it still is. It is also known as algodystrophy, Sudecks atrophy and a host of other names. None of these names are appropriate. It is now called, by the International Association for the Study of Pain, a complex regional pain syndrome. This is a syndrome of continuous, diffuse limb pain, often burning in nature and usually consequent upon injury or noxious stimulus and disuse. It presents with various sensory, motor, autonomic and trophic changes. Causalgia represents a specific presentation of this syndrome, associated with peripheral nerve injury (as described by Wier Mitchell).
A complex regional pain syndrome Type II then is exactly the same as the first one, except that there has been nerve injury leading to the syndrome. By nerve injury, we mean an obvious nerve injury, whereby there is loss of sensation over the distribution of a peripheral nerve.
When doctors are faced by a phenomenon which exists, but which they dont understand, they invent reasons for it. These reasons may be based on a recent article they read in the Times, or some pearl of wisdom they heard from a Professor whilst they were medical students 30 years ago. If this conventional wisdom is repeated enough times, it then becomes fact. It is to avoid this error that we are now being encouraged to look at evidence-based medicine. Although this is a dreadful burden, given our past performance it is hardly surprising that we are being encouraged to do this.
The experimental findings that damage to nerve tissue in rats resulted in a sympathetically-maintained state led doctors to extrapolate them to this being the cause of the condition. Careful investigation reveals that this is not always the case. The situation then is further complicated by the fact that some of these conditions are sympathetically-maintained and some of them are not. Thus now we have the concept of sympathetically-maintained pain and sympathetically-independent pain. This is quite simple, because we can test for this. If we block off the sympathetic nervous system and the pain goes away, but it doesnt go away with a placebo, then this is sympathetically-maintained pain. If it doesnt go away at all, or if it disappears both with sympathetic blockade and with placebo, then it is sympathetically-independent pain. Some CRPS Types I and II are SMP, some are SIP. Some have elements of both.
Clinically, at the moment the label of RSD is quite practitioner-dependent. It ranges from a hyperalgesic, sweaty, oedematous, cool appendage to simply any surgical outcome that fails to meet the expectation of the operating surgeon. Many Physiotherapists make the diagnosis in any patient complaining of a pain in a limb, where there is no specific explanation as to the reason for that pain. Some 85 per cent of the patients referred to me with an RSD do not have sympathetically-maintained pain. This can lead to treatment which is inappropriate for some, and other patients where specific useful treatments are overlooked and ignored. Consider the case of a patient who dropped a can of soup on her foot whilst walking around the kitchen in slippers, causing injury to a branch of the superficial peroneal nerve. She had pain in this region; there was no erythema and no oedema. She had hyperalgesia to light touch in that branchs territory and she had some numbness and abnormal somatosensory testing. She had been diagnosed as having RSD and had multiple Guanethidine blocks without any specific pain relief. This was a superficial peroneal neuralgia and not an RSD.
Where did the whispers come from that made us think that this was a sympathetically-maintained pain state in all cases? Animal models establish an important role for the sympathetic nervous system in many forms of neuropathic and inflammatory pain. Damage to rats sciatic nerves by tying them, and other damage, gives rise to a syndrome that we could recognise as a complex regional pain syndrome in humans. Sympathectomy is often effective. However, there are qualifications here. In some groups it is only effective during the first 10 days after surgery. In other groups, it affects only thermal hyperalgesia. Pre-emptive sympathectomy has been used and is helpful in some rat groups but not in others. These data then support the involvement of the sympathetic nervous system in neuropathic pain, but they emphasise the different level of contribution and the time course. Obviously in these cases nerve damage has occurred.
Work by Wall showed that even when no obvious nerve damage occurred, any trauma could lead to disruption of nerve axons. This disrupted axon will then produce axon sprouts. These sprouts try to link up with each other and heal the nerve. If they do not link up with another sprout, some die and some lie there; if a collection lie there together they are known as a neuroma. However, it is clear that sometimes there are not enough axons to form any anatomical structure and this is a microscopic finding. However, this axon is exquisitely sensitive to noradrenalin, and any noradrenalin released in the area produces intense stimulation of the nerve, producing severe pain. This is made worse by light touch, stress and movement.
In humans, it is also clear that there is good experimental evidence that in some cases the sympathetic nervous system is involved in the maintenance of this pain state. In these patients, injection of noradrenalin into the affected area causes intense pain, whereas in you or I a small dose of noradrenalin injected subcutaneously causes no discomfort whatsoever. Injection of local anaesthetic into this area stops the hyperalgesia. Injection of sympathetic blocking agents, such as Clonidine or Phentolamine, in this area produces alleviation of pain also. Injection of placebo has no effect.
The problem is that, because these syndromes are over-diagnosed, and then treatments are carried out on people who do not have sympathetically-maintained pain, most placebo-controlled trials of therapy do not show that sympathetic blockading treatment is effective. This includes sympathectomies, Guanethidine blocks and some medication trials.
To re-iterate. What most of us think of as an RSD is in fact a complex regional pain syndrome. There has to have been an injury. There has to be pain out of proportion to that injury, perhaps accompanied by hyperalgesia. There has to be oedema or skin blood flow changes, compared with the other side, or abnormal sweating. Investigations can show whether or not this is sympathetically-maintained. If a nerve has been damaged, and there is clinical evidence of this, this is a CRPS Type II.
Sympathetically-maintained pain. This may be a mechanism for production of pain in a number of disorders. These include herpes zoster and post-herpetic neuralgia, other neuralgias, phantom pain, metabolic neuropathies such as diabetes and complex regional pain syndromes. It may exist independently, that is, there is no damage to nerve tissue, there is no history of injury but it has just developed in a limb. It is diagnosable only by means of placebo-controlled sympathetic blockade. Thus a person cannot be said to have it unless this has been done. They can be suspected of having it, in which case the test should be carried out, as it is relatively simple. The best test is a Phentolamine test.
Management of Complex Regional Pain Syndromes, with or without sympathetically-maintained pain. The only difference here is that, if there is sympathetically-maintained pain then sympathetic blockade is clearly indicated. However, the basic management is aimed at restoration of function, that is, a reduction in disability, and pain relief techniques which are safe and which allow this are legitimate and should be encouraged. These include the following:-
i. Analgesic drugs.
iv. Alpha adrenergic blocking drugs, such as phenoxybenzamine (cf Phentolamine), also prazocin.
v. Beta adrenergic blocking drugs, eg, propanolol.
vi. Calcium channel blocking drugs.
b) Stimulation techniques
iii.Dorsal column stimulation.
c) Nerve blocks and surgery
ii.Sympathetic ganglion blockade, eg, stellate, lumbar, Guanethidine blockade.
iii. Surgical and neurosurgical techniques seem to make things worse, which is hardly surprising if the condition in the first place arises from some type of nerve damage.
d) Physiotherapy, physiotherapy and more physiotherapy
The aim is to promote movement by the patient of the affected part.
e) Behavioural and cognitive aspects
The patient needs to take an active role in their own rehabilitation. Psychological support and encouragement can be given. This should be provided at 6 months.
f) Multi-disciplinary management
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