What is central sensitisation?
Essentially, central sensitisation is when an area of the CNS is exposed to prolonged pain stimuli, leading it to become more sensitive over time and eventually spreading to other previously non-painful areas.
Central sensitisation was originally observed in animals, when it was found that repetitive stimulation of C fibres increased dorsal horn stimulation. This phenomenon was called “wind up” and is thought to be one mechanism in which prolonged pain causes a hyperexcitable state in the central nervous system (CNS).
Sound super complicated but hold with me whilst I explain and everything will get clearer!
Pain impulses originate in nerve endings called nociceptors – we are particularly interested in A delta and C nociceptive fibres when talking about central sensitisation. These fibres carry the impulse to the dorsal horn neurons in the spinal cord. Some neurons are multi-modal (e.g., touch, pressure, temperature) but some focus on feelings of pain. Persistent pain causes the A delta and C fibres to be constantly activated. This leads to a flood of neurotransmitters and neuromodulators to be released into the dorsal horn synapse. This then sensitises wide range neurons (WDR) so that they become hyperexcitable. Over time they will need less levels of nociceptive stimuli to become activated and even previously non-painful stimuli will begin to activate them.
This prolonged activation of WDR neurons then activates surrounding neurons leading to an expansion of the “painful area” beyond the original injury. This then results in previously non-painful areas becoming painful when stimulated.
So, what can we do about it?
Pain Education
Where central sensitisation is present, it is important to change maladaptive illness perception, alter maladaptive pain cognitions and reconceptualise pain. This can be done a variety of ways including face to face session, written materials and by watching informational videos.
Using a CBT psychological model, there are three “layers” to maladaptive beliefs: core belief, intermediate belief and automatic thoughts.
Automatic thoughts are brief streams of thought about ourselves and others. Often because they are so brief, we are unaware of them. These thoughts become maladaptive when they become distorted.
Intermediate beliefs are rules we live and act by. We have created these “rules” based on information from the world around us. These rules tend to be “if Y, then X” for example, “If I am always in pain, no one will love me.” These rules guide our thoughts and subsequently our behaviours.
Dysfunction core beliefs drive intermediate beliefs and automatic thoughts. These core beliefs are often forged in childhood and then solidified over time due to your perception of events and experiences. The above intermediate belief “If I am always in pain, no one will love me” may actually be driven by the core belief “I am unlovable.” This may drive you to hide your pain, develop addictive behaviours (such as drugs or alcohol) to mask your pain or not seek appropriate treatment.
By identifying these beliefs, it is possible to replace them with more positive beliefs and thoughts which in turn will help you manage and improve your pain.
Pain reconceptualization involves helping people to understand things like the level of pain does not provide a measure of damage to the tissue. It can also help to understand that the relationship between pain and tissue damage actually becomes less predictable as pain persists. The experience of pain is also dependent on may other factors across a psychological, sociological and biological domain. Understanding that pain is perception of the risk of damage to the tissues and that this may become sensitised over time as explained above. Reconceptualising pain in these ways helps people to understand that just because it hurts when they move does not mean they are causing more damage and therefore they will not make things worse.
Manual Therapy
Manual therapy can help with central sensitisation by producing analgesic (pain reducing) effects and activating descending (from the skin towards the CNS) anti-nociceptive pathways for a short duration. Some speculate that manual therapy over repeated sessions may lead to long term activation of the descending anti-nociceptive pathways. There is also a chance the at manual therapy could potentially make central sensitisation worse if it activates peripheral nociceptive pathways – therefore, manual therapy should be delivered carefully and by a fully trained professional only.
Medication
Medication should only be used under a medical professional’s guidance, especially if over a prolonged period, as some drugs have serious side effects if they are taken for too long.
Some of the most common medications I see used are:
- Gabapentin/Pregabalin
- Paracetamol
- Amitriptyline
- Tramadol
A combination of the above measures is thought to be the most appropriate treatment for central sensitization as far as we know. Research is still ongoing and no doubt more effective treatments will come to the fore as our knowledge grows.