Pain is Complicated
Pain is a complex phenomenon and is only fully approached by employing what is called the “bio-psycho-social” model which reflects the different domains of human experience (biological, psychological and sociological) which can affect the total perception of pain.
There are different types of pain.
Chronic Pain: the terms “Acute” and “Chronic” refer to the duration of the pain i.e short or long duration, rather than the severity of the pain. Often a problem that has lasted more than 3 months is described as chronic.
Simple and Complex Spinal Pain: A pain problem may last for years and remain a “simple” problem, i.e. it affects or 1 or a limited number of structures (a single disc) or it may become “complex” with several things contributing to the pain (a disc hitting a nerve and causing stress on the facet joints behind ie 3 things generating pain).
Somatic pain: arising from injury to a bodily structure such as a disc, a facet joint or the sacro-iliac joint. This is the typical ache or throb (toothache) that we are all familiar with after a knock or strained ankle etc.
Neuropathic pain: refers to pain arising from irritation of a nerve tissue or within the brain and nervous system itself.Neuropathic pains do not respond well to common painkillers but do to old fashioned antidepressants used in low doses, usually at night (amitriptyline or nortriptyline) or to more modern anti-convulsant (anti-epilepsy) drugs which can be used during the day (Gabapentin or Pregabablin).
Peripheral Neuropathic Pain: this is pain that arises from irritation of nerve structures such a spinal nerve root such as occurs in “sciatica”. It is often severe and has a tingling (pins and needles) or numbing quality. It often responds well to anti-inflammatory injections with steroid.
Central Neuropathic pain: the brain and nervous system are highly evolved to feel pain. In certain situations, persisting painful stimulation (eg from a persisting disc injury) can cause the sensory system change and to adapt towards increasing pain sensitivity. For example, in the spinal cord, persisting irritation at one level (say S1 in sciatica) can cause the adjacent segments to activate which is felt by the patient as the pain spreading. Then the spinal cord starts to “recruit” nearby pathways and to activate those, for example causing the sensation of light touch to be felt as pain. The higher nervous system can also become over-activated creating emotional and other effects and mutiplying pain.
Pain and the Brain: Ultimately all of these factors are put together and perceived (felt or experienced) in the highest areas of the brain where the influence of learned experience, beliefs, worries, unrelated everyday stresses, hormonal effects and many other complex factors play a part in the overall perception of the pain problem. To put it this way, the person you are determines the pain you feel.
Modern functional MRI imaging has illustrated how persisting pain can and does alter various connections and pathways in the brain, and is capable of adapting the brain towards the pain, even to the extent of changing the shape and size of parts of brain. In short, pain is very much in the brain (as well as the back), but that does not mean it is imagined or made up”.The good news from these studies is the finding that once the source of pain is removed, these alterations in brain pathways can return to normal.
Mood Fatigue and Pain: as a result of these well documented biological effects in the nervous system, alterations in mood and fatigue are the handmaidens of chronic pain and almost always occur. Mood, fatigue and pain are all linked and are almost inevitably react to one another. When pain increases, mood goes down and fatigue goes up, when mood goes down, pain goes up, etc.
Fibromyalgia Syndrome; Pain is not a physical object but a sensation – a perception created by the neurological activity of the pain sensory system in the brain. For various reasons, many of which are quite well understood, some people are predisposed to the nervous system reacting to chronic painful stimulation by increasing sensitivity to the pain, rather than ignoring it as would perhaps be more “useful”. The result may be the development of complex pain with all of the features described above: apparent spreading of the area of pain, the recruitment of non-painful stimuli (light touch becomes painful), increase in severity of usual pain and pain in undamaged structures, fatique, mood disturbance including depression, disturbance of thought, concentration and symptoms of other sorts. When fully develped this complex situation is often described today as Fibroymlagia Syndrome (FMS).
A variety of physical, psychological or social factors can dispose to FMS. In my practice, chronic spinal pain and sleep disturbance are the common ones.
Sympathetic Pain: just to add a little complexity, many of the small nerve fibres which convey pain into the central nervous system travel with the sympathetic nerves which principally regulate blood vessels and automatic functions (heart rate, sweating, gut movement). Often these pains are felt as cold, hot or associated with alteration of colour in the affected limb/foot. There are no drug treatments for sympathetic pain but it an be managed in part by blocks and other interventions.
So, there may be a lot more to pain than meets the eye and spinal pain is, legitimately, difficult. The proximity of nerves/neural structures spinal, joints and the curiosities of intervertebral disc pathology may all merge to give a highly complex picture with a significant tendency to central pain activation (central neuropathic pain).