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Every millimetre of our body (except the brain) has its own nerve supply. If one foolishly sticks a pin anywhere on our living tissue, we would be able to feel it as pain. I emphasise living tissue, as clearly our nails and hair would not be included. Where they arise, there is however exquisite tenderness as anyone with a nailbed infection, or an infected scalp would know.
Pain is transmitted by unmyelinated type C nerve fibres. They carry the pain sensory impulses from the periphery into the spinal cord. These nerves that gather together into the larger sensory nerves. These then enter the spinal cord by the dorsal root having formed what is known as the dorsal root ganglia. The pain fibres go into the spinal cord and form the spinothalamic tract. This will run up the spinal cord into the deep structures of the brain including the thalamus. The thalamus also then sends projections into different parts of the brain including the frontal lobe. It is lay experience that if a cut or injury occurs to the skin it generates pain. Perhaps the best example of this would be a paper cut or falling on the ground and scraping a knee which is probably in the experience of most of us when we were younger (or much older). When such an injury occurs, tiny nerve fibres are cut, and this then generates pain. The sensory pain receptors object strongly to the damage inflicted. A message is sent immediately into the central nervous system advising that injury has occurred. This may lead to acute withdrawal as a reflex phenomenon. This embedded responsiveness is in fact essential to our total survival. There are a very small group of people who through genetic and developmental reasons do not have either of these pain fibres or the ability to appreciate pain. This condition known as a congenital indifference to pain syndrome is a subject for another time.
Simplistically, it is everything to do with surgical incisions through the skin. However skilled a surgeon there is still a need by whatever means to make an opening in the skin in order to do whatever is necessary. Whether this is removing a piece of skin itself as a biopsy or cutting through the skin to get to all the layers of tissues beneath the same principle applies. As every millimetre of skin carries pain receptors, this means that the surgical incision is no different to any other trauma. It is more deftly undertaken and with a greater regard to avoiding more serious structures, but it is still damage to the skin and other tissues beneath. Because the cutting of tissue is so painful it requires the use of local anaesthetics if a local procedure can be undertaken. The use of general anaesthesia with powerful pain relief essential for the more fundamental procedures of surgical intervention. So called regional or spinal blocks do exactly the same. They remove the ability of the individual to appreciate the pain of the surgical incision and then the underlying surgical intervention. As the local anaesthetic or general anaesthetic wears off, pain is an inevitable consequence. Modern pain management allows for this discomfort or even severe pain to be reduced or blocked according to need. For the vast majority of people, the wound pain will settle over a number of days to weeks. There are regrettably a small percentage of people for whom the pain in the scar and underlying tissues continues and becomes chronic. Surgeons are aware of this phenomenon. For instance, when dealing with the simple but skilled procedure in repairing a hernia, a small number of people will get pain in their scar even though the hernia has been successfully repaired.
After the surgical procedure there is usually an angry looking scar with sutures or clips or even a suture that runs under the skin. The skilled surgeon will oppose the edges of the scar. For most people there will be a good cosmetic result. Some people do get thickening of the scar by a process known as keloid. This is usually nothing to do with the pain syndrome that can emerge. The human body reacts to skin damage by sending various cells types and chemicals into the damaged area in order to try and effect a repair. Once there is healing and integrity of the skin, then the scar tissue begins to contract down by a process known as fibrosis. The thickening of scar tissue that is normal, will over the course of many months shrink down and tighten. What however can be forgotten, is that same tightening and fibrosing process is taking place at every level through which the surgeon has needed to both cut, possibly suture or diathermy blood vessels and then finally apply sutures to close each layer. Each part of this process will both tie and damage the tiny nerve fibres that are going into each layer of tissue. As the tightening of the scar occurs with fibrosis then these nerves will get bound into that scar tissue.
It may be that there is a genetic predisposition for the small number of people that get scar pain. The scar pain itself can be particularly unpleasant. The pain is generated by the damaged nerves and is a form of neuropathic or nerve pain.
Nerve or neuropathic pain is generated when a neural element is damaged. Usually this will be a peripheral nerve or nerve root, that is the part of the nerve that is just before the spinal cord. Nerve pain of a different type however can arise from damage within the spinal cord and certain deep parts of the brain such as the thalamus, but that is not part of the current discussion.
When a nerve gets damaged, particularly if it is a sensory nerve, in effect it is just doing the job that it was intended. It will generate a message along its path into the spinal cord and then into the central nervous system confirming that there is damage. What it is not able to confirm is that the damage is actually in itself rather than just in the tissue that it supplies. The difference however between pain arising for instance from a scar is that the usual healing process allows equally for the peripheral nerve receptors and nerve to come a new balance and the pain pathway is then effectively switched off. It is those small number of people do not switch off that neural signal either as a consequence of the scar tissue itself and the small nerves that are trying to regrow into it, or because the nerve itself is damaged and not able to switch off the abnormal signal.
There is one specific different situation, which is not the subject of this discussion, but can still generate pain. This is when a peripheral nerve is cut. It is possible then for a small nodule to form on the end of the nerve known as a neuroma. A neuroma itself can be locally painful as well as send pain signals more centrally. This condition is however a different one to the subject of this discussion.
The simple answer is that the reason is not known. I suspect that there is a major genetic influence as to why some people are so sensitive. This would not be a surprise given for instance, our knowledge that migraine sufferers have a significant genetic association. There are also many other painful conditions that seem to depend on the genome. It may also reflect the nature of the scar or the circumstances by which the surgical procedure has been carried out. For instance, an individual having operations for polytrauma caused unexpectedly by a severe road traffic accident or other traumatic process, or emergency surgery, may well be more likely to get scar pain than an individual having an elective procedure. There is also mounting evidence that the way in which the surgical process is carried out and in particular the anaesthetic with pain relief given at the time of the surgery may also contribute to a lower risk of scar and neural pain. It has been considered that scar pain is different to neuropathic pain, but I hold the opinion that they are effectively the same on the basis that the scar tissue itself is not capable of generating pain, it is the stimulation of the neural receptors and the nerve itself closely opposed to the scar that lead to the pain.
As mentioned above, the use of appropriate analgesia before and during the operative procedure seems to lead to a reduced instance of post-operative pain generally. In the same way the close and qualitative management of post-operative pain also seems to reduce subsequent pain in and around the wound. There are significant psychological and emotional considerations as well with regard to the management of the individual at the time of the surgical procedure. In my experience it would seem that this is complication is rarely discussed with people before the operation. They may not realise that getting good pain relief is not just important for post-operative wellbeing, but it actually reduces the likelihood of late surgical pain. It is not a sign of weakness of the individual to want more pain relief.
Given that the primary need of all doctors is the management of pain, it is remarkable to consider how poor at times we are in that management. We are limited to only a few treatments including paracetamol, aspirin, anti-inflammatory drugs, and various forms of opiates. There are different medications that can be used in the management of more chronic pain as discussed below, but the medications mentioned are those that we have in order to control acute pain. If pain management and rehabilitation in the UK are somewhat Cinderella specialties with limited resources, then management of scars is not even close to that inadequacy. Often the only advice given is to massage some cream into the scar, but often this is given as an afterthought without any great confidence or the advice as to who should do this, how much pressure to apply, or even when to start. As discussed earlier, it is not just the skin that is scarring and tightening, but it is at all the levels beneath.
Specialist physiotherapists know how to manage scars effectively and to loosen the tissue by various different techniques. It is my view that every person having a significant surgical procedure involving a scar say more than three inches, ought to be referred for appropriate specialised scar management. If the scar has to go across a joint or for instance if it involves the hand, then under these circumstance physiotherapists are vital to the maintenance of movement and there will always be such a referral made. It does not seem to be routine however for people who have scars from a caesarean section or even an abdominal operation or a hip replacement.
Ideally if a scar continues to hurt or generate a nerve pain at six weeks after surgery latest, there should be a referral to a neurologist with an interest in pain management or pain specialist. It must be assumed at that point that the surgeon is content with the scar and that there are no retained sutures or any evidence of developing infection. Such occurrences are usually obvious by virtue of either the excessive reddening or swelling of the scar, the presence of fever, the fluctuation of soft tissues around the scar or even the discharge of pus. At six weeks the wound should be healed, sutures have been removed usually for about a month already and an individual should be reconditioning in order to get back to their previous level of fitness.
With a referral to a consultant neurologist or pain specialist a history will be taken. The individual will be asked to keep a pain diary noting the level of pain on a 0-10 visual analogue pain scale as well as recording other aspects of their life that might be a negative input with regard to their psychological and emotional state.
Usually, analgesia will have finished by six weeks, but there is no harm in continuing simple analgesia whilst the primary assessments are taking place. The careful application of cold, occasionally hot, and gentle massage and vibration may be beneficial. Once it is confirmed that the problem relates to the scar and nerve pain with no other disorder, then medical treatment has to be considered.
There are four modalities of medical treatment. These are physical, injection, talking and pharmacological therapies.
Physical management involves engaging with physiotherapists and occupational therapists. The physiotherapists should be well versed in the management of scar tissue. They have a number of techniques that can assist including a more skilled and deeper tissue massage and also the use of carefully applied suction to the scar tissue in order lift it from the tissues below. They can also demonstrate how you or a partner can continue the same massage twice each day. Physiotherapists, depending on the position on the scar and also assuming there are no contraindications, could consider acupuncture. They may also consider a trial of a TENS machine which is an electrical stimulator device. Occupational therapists have a complimentary role in helping with desensitising techniques, so that the mind is less focused on the pain in the same way that talking therapies and psychologists well versed in pain management can also assist with distraction management. Some consultant psychologists will also consider using clinical hypnotherapy as a way of desensitising the pain.
These treatments will need to be supervised by either a consultant neurologist with an interest in pain management or a consultant who specialises in pain. These consultants are often consultant anaesthetists who have extended their skills providing often more invasive types of treatment, but also using pharmacological therapies. Many people seem to go along a non-pharmacological line first. If all the other three types of treatment do not help then concurrent with continuing these treatments, a number of pharmacological agents can be tried. These treatments can be taken by mouth or they can be applied to the skin. The three main agents that can be applied topically include a local anaesthetic patch, the application of what is known as capsaicin cream, or an anti-inflammatory gel. Much to the consternation of neurologists and pain specialists, the NHS has elected not to allow the prescription of the lidocaine 5% local anaesthetic patch for reasons that are illogical and poorly considered. These patches applied near to or around any painful area either work or they do not. If they work, they are remarkably free of side effects. If they do not work, they are not going to be repeatedly prescribed. An individual will usually know whether they are effective within the first week of application. This means that often a private prescription will need to be given. The capsaicin cream will need to be prescribed but the anti-inflammatory gels can be purchased over the counter.
Regarding tablet treatments the medications fall into the anti-depressant group, the anti-epilepsy drug treatment group, or occasionally orally acting local anaesthetic. More powerful psychoactive agents occasionally may be considered when everything else has failed, but usually a psychiatrist will be involved.
Depending on where the pain arises and the placement of the scar, sometimes local injections into and around the scar may be beneficial and this will be in the province of a pain specialist. In the very worst pains when everything else has failed, then more invasive injection type treatments can be considered. The discussion on these is probably outside the brief of this article. Only a very small number of people will need to have such invasive treatments considered. There are many medications within these different groups and if one drug treatment were effective then it would be a very straightforward process. Regrettably, this is not the situation and the great skill in pain management is finding the dose of the right drug for each individual patient. In all pain management it is essential that the suffering person is on the same team as the managing consultant. Sometimes, people are on the same pitch but different teams and then management is difficult. If the relationship is such, that either the consultant or the patient feels that they are on different teams on a different pitch for whatever reason, then it is best that each recognises the problem, and an alternative opinion needs to be sought.
Scar pain is much under-recognised. It does affect a small percentage of people having any operative intervention. It can only be diagnosed by the history and absence of any other cause. Early treatment of the syndrome will give a greater chance of successful resolution.