Pain mechanisms

Understanding pain mechanisms is the key to effective treatment. The mechanisms that have been studied, written about in science journals and discussed with patients include nociceptive pain, inflammatory pain, neuropathic pain and central sensitisation. Elucidating which are playing a role in the patient’s experience allows the doctor to prescribe the right medication and the modern physical therapist to address the issues of pain in a biopsychosocial manner. I will now clarify the latter point.

In taking a detailed history, observing patterns of movement and protection, assessing the state of the nervous system and health of the body systems, understanding behaviours and the beliefs behind them and learning of the influences upon the individual’s pain experience, one can know about the likely pain mechanisms underpinning the experience. From here the treatment strategies can be chosen to target these mechanisms. For example, top-down approaches for central sensitisation focus on the change in the properties of the central nervous system. The interventions themselves are observant of the amplification that occurs in the spinal cord and higher centres and would seek to dampen the responses with input to the brain that is perceived as normal or non-threatening. This could include sensory stimulation or movements outside of the receptive field, education to reduce fear of movement or imagery to name but a few. Inflammatory pain can also be treated with a top-down approach but local tissue based strategies would also be used. Just to note that the separation of the ‘top end’ (brain and spinal cord) from ‘bottom end’ (tissues) is really a false dichotomy as all conscious experiences are from the brain including what we see and what we feel.

Stephen McMahon and David Bennett, both experts in the field of pain science from King’s College London, produced a poster that describes these mechanisms – click here to visit the page in Nature Reviews Neuroscience. This is what they say about it:

Pain is an unpleasant sensation resulting from the intricate interplay between sensory and cognitive mechanisms. Chronic pain, resulting from disease or injury, affects nearly every fifth person in the Western world, constituting an enormous burden for the individual and society. Sensitization of pain signalling systems is a key feature of chronic pain and results in normally non-painful stimuli eliciting pain. Such sensory changes can occur not just at the sites of injury, but in surrounding normal tissues. This and other observations suggest that sensitization occurs within the CNS as well as within nociceptor terminals. Here we consider the consequences of noxious stimulus applied to our unfortunate builder’s hand, from sensory transduction to pain perception. We describe the structural and functional elements present at different levels of the nociceptive system, as well as some of the changes occurring in chronic pain states. Although our poster highlights a flow of information from the periphery to the CNS, it should be noted that higher brain centres exert both inhibitory and facilitatory controls on lower ones. The challenge for the next decade will be to effectively translate this knowledge into the development of novel analgesic agents for better pain relief.

Richmond StaceSpecialist Pain Physio Clinics, London & Surrey

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