Overview 

Central pain syndrome (CPS) is a condition characterised by chronic, persistent pain, often described as feelings of burning, aching or tingling sensations. In this article, we will explore the brain’s ability to adapt, a useful mechanism for learning, and how it can go wrong sometimes. The brain can form harmful connections, and in people with CPS pain, it gets ‘stuck’ in the wiring of the brain, leaving them with lasting pain. 

What can we learn from disorders such as CPS? What do they teach us about pain and how to manage it? We will explore these topics and provide a deeper insight into living with chronic pain conditions.¹

What is CPS?

CPS is a neurological condition. It occurs when damage to the brain or spinal cord leads the nervous system to malfunction. People with CPS experience chronic pain, often in the form of burning, stabbing, itching, numbness or aching sensations, as well as tissue and muscle pain. CPS can be caused by conditions such as strokes, spinal cord injuries or degenerative diseases of the central nervous system (CNS). Chronic pain from injuries or other centralised pain disorders can also result in a person developing CPS.

CPS is characterised by the nervous system becoming overly sensitive to pain signals. Neurons will either amplify pain signals in response to minimal stimuli or even fire pain signals without any input. When this happens, your brain and nervous system are telling you that you are in pain, when no physical harm is occurring to your body.²

Why do we feel pain?

The human body interacts with the surrounding environment through our nervous system. This is how we sense the world around us. We have specialised nerve endings called nociceptors, which help us to detect painful stimuli. When these specific pain receptors are activated, they send signals through your spinal cord to your brain, which you then perceive as pain.³

As strange as it may sound, pain is both helpful and essential. Feeling pain indicates to us when we are hurt, acting as a warning signal, which helps us survive. Pain helps us to avoid further injury and protect ourselves. But what happens when pain-signalling pathways go wrong, and why do some people experience chronic pain?

What happens to the pain circuitry in CPS?

 As there are no external stimuli to cause the pain that individuals feel in CPS, it is described as a centralised pain, originating from the brain or the spinal cord. Hence, it can be said that the nervous system is in a state of hyperactivity.²

What causes CPS?

The CNS is made up of the brain and spinal cord, and when damaged, it can lead to the development of CPS. This damage can be a result of a number of conditions, such as: 

• Stroke 
• Traumatic brain injuries 
• Spinal cord injuries 
• Degenerative conditions of the nervous system (such as multiple sclerosis) 
• Brain cancers

Chronic pain, caused by conditions such as arthritis, back pain, cancer, irritable bowel syndrome or inflammatory conditions like rheumatoid arthritis, can also cause CPS. Chronic pain has a significant effect on the nervous system and, over time, can cause your nerve cells to become overly sensitive to pain signals or misinterpret non-pain signals as pain signals.²

What is neuroplasticity? — How the brain adapts

 The brain can reorganise itself, learn and grow by making new connections throughout your life, and even remove ones that are no longer useful. This ability of the brain to adapt in response to one's experiences is called neuroplasticity.⁵ 

A good example to help explain this is learning a new skill. Have you ever heard of the term muscle memory? This is a great example as it demonstrates how the repetitive actions you make while trying to learn a new skill, such as riding a bike or even touch typing, eventually become ingrained into your nervous system. Over time, these actions become like second nature and require less thinking as the brain has the ability to learn and recall actions. 

Your nervous system is made up of nerves which connect to each other at their ends. We call this junction where the two nerves meet a synapse. Nerves pass on information in the form of an electrical impulse, and these interactions can change over time. A certain amount of stimulus is required to activate a nerve enough for it to send an electrical impulse along it and onto the next neuron. This is referred to as excitability. After a repeated stimulus, a nerve can adapt and require less of a stimulus to generate and send a signal. 

We can also see other changes in the way the nerves work and interact. Nerves send signals by releasing chemicals into the synapse, which are taken up through channels on the receiving nerve. These are called ion channels. Nerve cells can increase the number of ion channels at their synapse, meaning more pores through which the chemicals carrying the “signal” can pass through, into the next neuron. These channels can become more sensitive and hence, easier to open. Nerve cells also use inhibition as a mechanism to stop unnecessary signals being sent to the brain, an essential regulatory process of your nervous system. These inhibitory mechanisms can be harnessed and used to reduce neuronal activity in people who have conditions of centralised pain.⁶

Maladaptive pain circuits

Neuroplasticity can, in some cases, go wrong. As the brain and nervous system are constantly adapting, activated pain pathways after an injury to the brain or spinal cord can become more ingrained into your nervous system.⁷

We see physical and structural changes to the nerves, essentially a rewiring and strengthening of certain pathways, making them more prominent and sensitive. The nervous system’s ability to change in situations like these can backfire in people with CPS, and cause hyperalgesia (heightened or intensified feeling of pain) and allodynia (feeling pain from a non-harmful stimulus). This means the nerves that detect pain react more often than they should be reacting at all. This phenomenon is known as central sensitisation. 

Internal effects and chronic pain 

Interestingly, we can experience pain without physical stimuli; however, places and thoughts are able to trigger the sensation of pain as your nervous system can remember painful experiences. This memory can influence how we feel pain in the future.⁹

This highlights the role of many factors that can affect our perception of pain, such as old injuries, emotions, and oversensitivity to external stimuli. These underlying mechanisms help us understand the complexity of persistent pain and how different factors influence it, ultimately facilitating pain management strategies. 

Management and treatment  

Pain is subjective; it is a personal experience with no objective or quantitative way to be measured, which can make it difficult for people with CPS to receive a diagnosis. Chronic pain is debilitating, often overlooked and misunderstood. Hence, finding the appropriate management strategies for patients can be a challenge. 

Normally, affected individuals would take pain medications such as ibuprofen (an anti-inflammatory drug (NSAIDs) or opioids (much stronger pain killers which have a blocking effect on pain) to relieve pain; however, these painkillers are often ineffective for people with CPS. 

Alternative pharmacological interventions used to manage pain in people with CPS include:

• Antiseizure medications like gabapentin
• Tricyclic antidepressants (TCAs) such as amitriptyline or nortriptyline
• Antidepressants, specifically serotonin-norepinephrine reuptake inhibitors (SNRIs)

Living with CPS or any chronic pain is challenging and can take a significant toll on an individual’s life. People with CPS often experience trouble sleeping, fatigue and mental health conditions such as depression or anxiety. Therapy, such as cognitive behavioural therapy (CBT), can be implemented into management plans to help individuals cope with chronic pain.² 

Can we unlearn pain?

 The chronic pain that we see in people with conditions such as CPS is almost like a persistent memory of pain that won’t go away. We know that the brain can undergo plasticity; however, the brain gets stuck in overdrive in these conditions. So, it is possible to assume that we can retrain the brain to unlearn this pain. Studies have explored this idea and have found potential for implementing neurostimulation into therapy to manage pain. 

Neuromodulation methods used to manage chronic pain in people with CPS include:

• Deep brain stimulation (DBS)
• Motor cortex stimulation (MCS)
• Peripheral nerve stimulation 
• Repetitive transcranial magnetic stimulation (rTMS)
• Transcutaneous electrical nerve stimulation (TENS)

All these methods deliver electrical stimulation to different areas of the body to affect different parts of the nervous system. It works by having a modulating effect, altering the maladaptive pain circuits and the way the brain processes pain.¹⁰

Summary 

Central pain syndrome is a challenging and complex condition that greatly affects an individual's quality of life; hence, it is important to approach each person with CPS with tailored and specific management strategies that can help them manage their chronic pain.