Chronic Pain: Causes, Types, Diagnosis, and Treatments

This guide gives you all the essential knowledge on chronic pain. Understand what causes pain to become chronic, types of chronic pain, the diagnosis process, available treatments, and more.


What is chronic pain?

Chronic pain is pain which lasts longer than 3 to 6 months. Under the International Classification of Diseases (ICD-11) by The World Health Organization (WHO), chronic pain is defined as: “pain that persists past normal healing time and hence lacks the acute warning function of physiological nociception.” Nociception simply refers to how our bodies detect pain and send pain messages.

What are the symptoms of chronic pain?

Each diagnosis may have different specific symptoms. Symptoms can even vary from person to person with the same diagnosis. Some general symptoms of chronic pain usually experienced include:

  • Joint pain
  • Muscle aches
  • Reduced mobility
  • Stiffness
  • Lack of flexibility
  • Reduced functioning
  • Social withdrawal 
  • Fatigue
  • Insomnia
  • Mental illness (low mood, depression, anxiety, etc)
  • Hyperalgesia (increased sensitivity to pain)
  • Allodynia (finding things painful which should not cause pain, such as a touch on your skin)
  • Skin rashes and irritations
  • Sensitivity to temperature/problem regulating temperature
  • Cognitive problems

What causes chronic pain?

Chronic pain can have a variety of causes including the following:

An initial injury

An initial injury may not have been treated effectively or healed properly, which can lead to pain persisting beyond 3 months. Even if an injury heals well, it can lead to chronic pain. You might be wondering, how is this possible? Well acute pain is a protective defence mechanism. The brain creates pain to try and protect the body. For example, if you touch something hot, a danger message is sent to the brain. The brain then interprets the message and if it deems that protection is necessary, you’ll feel pain which in this case gets you to move your hand before you get burnt.

When you injure yourself, pain motivates you to protect the injured area. However once the injury has healed, the nervous system may have already adapted and become accustomed to sending out those pain messages in response to certain situations, events or stimuli and so continue to do so. Nerve pathways learn from their experiences, but they don’t always learn the right lessons. This is also known as central sensitization.

The injury could be something small such as a sprain or a fall, or something more severe such as being in a road accident or another physical trauma. Surgery can also start the cycle of chronic pain after the healing process is complete.

Illness

Sometimes an illness can weaken the body and make it more susceptible to chronic pain. Some illnesses may cause an autoimmune reaction (meaning the immune system is attacking itself), causing inflammation and other symptoms which lead to chronic pain. For example, rheumatoid arthritis is an autoimmune condition which causes inflammation in the joints. This can make it hard to move the joints and cause chronic pain. Sometimes the treatments of illnesses like cancer can lead to chronic pain, such as chemotherapy or radiation.

Nerve damage

Our nervous system controls every process in our body. Our nerves control the pain messages sent in reaction to outside stimuli, in order to keep us safe. When these nerves become damaged, the signals can be interrupted and incorrect pain messages can be sent out, leading to chronic pain. Nerve damage can be a result of many things including:

 

  • Too much pressure being put on the nerve
  • An area of the body being overused and strained
  • An accident
  • An injury
  • An illness (such as diabetes or an autoimmune disease)
  • Nutritional deficiencies
  • Misuse of drugs

Chemical imbalance

The chemicals within our brain must be balanced in order for our bodies and minds to function properly. These chemicals are neurotransmitters. They send signals (or instructions) around the body to control our biological processes. When chemicals in the brain become imbalanced, this can lead to symptoms of chronic pain among other health problems.

For example during prolonged stress, high levels of stress hormones are sent out. These hormones include cortisol (known as the stress hormone) and adrenaline. These hormones keep the body in a state of ‘fight or flight’, which is not designed to be endured for a long period of time. The effects of this over time (such as very tense muscles) can lead to chronic pain.

Since our brains are neuroplastic (which means they learn from what is happening in our environment) they learn and change. When the body is under a lot of stress, the brain ‘learns’ to keep sending out pain messages in response to perceived threats. The brain is trying to protect the body, even though protection is no longer needed.

Another example of chemical imbalance is low levels of serotonin, which helps to keep your mood stable as well as regulating emotions, sleep and your stress response among other functions. When levels of serotonin are low, it can cause a low and unstable mood. Since our bodies and minds are connected and can influence one another, an unstable mood can have physical consequences. If a patient has depression for example, they are less likely to be active, to eat healthy meals and to sleep well. This can lead to a decline in physical health. Inactivity can lead to deconditioning (essentially meaning lack of fitness) which can contribute to chronic pain.

How is chronic pain diagnosed?

When you first attend the doctor’s office they will evaluate your medical history and talk to you about your symptoms. In order to reach a diagnosis a number of tests may be carried out. These tests can give the doctor a better idea of what is happening within your body and help them to rule out other causes of your pain.

Some chronic pain conditions may have factors which show up on tests, while others will focus solely on elimination of other conditions and your description of your symptoms. The amount and type of tests carried out will depend on your individual case and what the doctor feels is needed to get a clearer view.

The tests carried out may include:

Physical examination

This simply means the doctor will examine your body with their hands. They may move your body into specific positions, put gentle pressure on specific areas and ask you which areas are painful. This is typically done within the doctor’s office.

Blood tests, urine samples, and joint fluid tests

These tests check hormone levels, look for indications of inflammation, check immune function and check for signs of other illnesses. As with a physical examination, these tests can be done in the doctor’s office.

X-ray

X-rays are a type of radiation which can pass through the body. They are detected by a machine and form an image on a screen for the doctor to look at later. X-rays check for any signs of damage in your bones and joints. You can’t feel x-rays, irregular exposure won’t hurt you, and it usually only takes a few minutes.

X-rays will usually be carried out at a hospital or clinic. You will likely be referred by your doctor and get a letter with an appointment date to attend the hospital as an outpatient. Once the x-ray is complete, the hospital will send the results back to your doctor, who will contact you to discuss the results and decide what happens next.

MRI (Magnetic Resonance Imaging)

An MRI is a scan which uses magnetic fields and radio waves to produce images of the inside of your body. This allows the doctor to look at your soft tissues, your brain and spinal cord, your bones and joints, and other areas of the body in detail.

An MRI scan will take place at a hospital. You will lie flat on a bed, which moves mechanically into a tube. The tube is the scanner. You will need to stay really still during your scan. The scan can last between 15 and 90 minutes depending on how much of your body the doctor wants to look at. This can feel a little bit worrying but it’s painless. You are able to talk to the radiographer through a two way monitor at all times, and you can have headphones or earplugs in to block out of the noise of the machine.

CT (Computerized Tomography)

A CT scan gives tomographic images which are clearer than a standard x-ray. The National Institutes of Health explains that CT, “refers to a computerized x-ray imaging procedure in which a narrow beam of x-rays is aimed at a patient and quickly rotated around the body, producing signals that are processed by the machine’s computer to generate cross-sectional images – or “slices” – of the body”.

A CT may be used to check for other causes of your pain. The experience is painless, and will typically only take between 15 and 30 minutes. This will usually be carried out in a hospital or clinic.

Ultrasound

An ultrasound involves a probe which gives off soundwaves at a very high-frequency. These waves bounce off different areas of your body internally and create a live image on a screen. This doesn’t hurt and you can’t hear the soundwaves. 

Most ultrasounds are external. Usually you will have some gel on your skin to allow the probe to move smoothly over your skin. You will have likely seen ultrasounds used on TV or in person in relation to pregnancy. This usually only takes a few minutes and will likely be carried out at a hospital or clinic.

You may be asked to rate your pain on a pain scale. The doctor may also ask you to keep a record of your symptoms at home over time, such as what they feel like and how they change over time. If they don’t ask, you could offer to do so as this can be a great way for the doctor to get a clearer insight into how your chronic pain is affecting your day to day life.

Remember that getting a diagnosis can take time. You might not get the right diagnosis straight away or you may find that you have to advocate for yourself. Don’t give up. Your experience is valid and your pain is real. You deserve to have the answers you’re seeking.

Types of chronic pain

Musculoskeletal pain

Musculoskeletal pain refers to pain which is in your joints, bones, muscles or the soft tissues around these areas of your body.

  • Arthritis: There are many forms of arthritis. Arthritis is a condition affecting the joints which causes pain, stiffness and inflammation among other symptoms.
  • Chronic widespread pain (CWP): This diagnosis is defined as pain “in at least 4 of 5 body regions and in at least 3 or more body quadrants (as defined by upper–lower/left–right side of the body) and axial skeleton (neck, back, chest, and abdomen).”
  • Fibromyalgia: Fibromyalgia (or Fibromyalgia Syndrome (FMS) could be classified as a type of CWP, as one of the main symptoms is widespread pain. Other symptoms include fatigue, problems with temperature control, muscle stiffness and many more.
  • Back pain: Back pain can be either musculoskeletal or neuropathic (explained below) in nature. Back pain is one of the most common types of pain reported.

Musculoskeletal back conditions include:

  • Ankylosing spondylitis: Ankylosing spondylitis is a type of arthritis which causes inflammation and pain within the spine among other symptoms.
  • Spondylolisthesis: Spondylolisthesis is caused when one of the vertebrae (the bones which make up your spine) slips out of position. As well as pain, symptoms include numbness and stiffness.

Neuropathic back conditions include:

  • A slipped disc: The vertebrae within your spine are cushioned by soft tissue known as discs, which protects the vertebrae during your normal day to day movements. If one of these disks moves out of place, or ‘slips’, it can press on a nerve and cause a great deal of pain. 
  • Sciatica: The sciatic nerve runs from the lower back to your feet. When pressure is put on the nerve it can result in a lot of pain. This pressure can be caused by a slipped disc as we mentioned above, by a back injury or by a narrowing of your spine where the nerve passes through (also called spinal stenosis).

Neuropathic pain

When the nervous system is damaged (through an accident or a stroke for example) or is attacked through an illness (like diabetes), this can result in neuropathic pain. It’s typically the somatosensory nervous system which is damaged. This is the part of the nervous system which picks up on stimuli (both internal and external) and processes it within the body.

For example if you touch your arm, it’s the somatosensory nervous system which senses that touch and processes it. If the nervous system is healthy, it would tell your brain that you’ve touched your skin and not raise any alarms. If the nervous system is ‘faulty’, it may tell the brain that the touch is a threat and should be painful. This is also called allodynia. 

Neuropathic pain can also present as hyperalgesia, which refers to an increased sensitivity to pain. This means that when you stub your toe for example, instead of feeling a small amount of pain which passes quickly, you could feel as though you have broken your toe. Hyperalgesia and allodynia can also be symptoms of other types of chronic pain. 

Types of neuropathic pain include:

  • Complex regional pain syndrome (CRPS): CRPS typically starts after an injury and is usually isolated to one limb, although sometimes the pain can spread to other areas of the body. Although there has been some debate over the years as to how to define CRPS, it is now defined as a neuropathic condition. As well as pain within the affected limb, symptoms of CRPS also include abnormal movement of the limb, abnormal sweating in the area and changes in skin texture.
  • Postherpetic neuralgia: After a patient has recovered from shingles (a viral infection), nerve pain can be left behind in the areas which were affected. As well as pain, symptoms can include excessive itching in the area, hyperalgesia and allodynia.  
  • Trigeminal neuralgia: Trigeminal neuralgia is severe facial pain caused by the trigeminal nerve being compressed. The NHS explains that the trigeminal nerve is, “the nerve inside the skull that transmits sensations of pain and touch from your face, teeth and mouth to your brain.” The pain can be extremely severe and can be triggered by normal day to day activities.

Headaches and orofacial pain

Headaches and orofacial pain are described as chronic when they occur on at least 50% of the days during at least 3 months.” Orofacial pain refers to pain felt in the mouth, jaw or face. This pain can come and go throughout the day or be more consistent depending on the individual and how well their pain is managed.

Types of headaches and orofacial pain include:

  • Migraine: Migraines are severe forms of headaches which can cause nausea, sensitivity to light (photophobia) and sensitivity to sound (phonophobia). Migraines can be triggered by stress or physical activity and can vary in severity.
  • Tension headaches: This type of headache has similar (but typically less severe) symptoms as migraines. Just as it sounds, tension headaches are caused by tension within the muscles around the neck and head. This can be caused by stress, anxiety or physical strain.
  • Trigeminal autonomic cephalalgias (TACs): This sounds really complicated but are essentially severe headaches which have additional autonomic (meaning nerve related) symptoms. These additional symptoms can include drooping eyelids and excessive eye watering among others. You might also hear TACs referred to as cluster headaches.
  • Chronic temporomandibular disorder (TMD): This is one of the most common types of facial pain. It affects the muscles around your jaw. As well as pain symptoms can include clicking or popping sounds when you move your jaw, a headache and problems with moving your jaw.

Post surgical pain and post trauma pain

After surgery or an injury (physical trauma), pain can persist. Acute pain has then become chronic pain. This can be because the injury didn’t heal correctly, because nerves have been damaged, or because the brain has learnt to continue producing pain (the central sensitization we mentioned earlier).

Cancer pain

Chronic cancer pain can be caused by cancer treatment, such as surgical treatment, chemotherapy or radiation. It can also be caused by the cancer itself, either by the primary tumour or a secondary site which has developed from the primary tumour (this is also known as metastasis). Sometimes these tumors can compress nerves causing neuropathic pain.

The type of pain associated with cancer can be experienced by patients as a constant, or it can come and go. Often when the pain is intermittent, it is triggered by outside stimuli such as stress, movement or continuations of treatment. The pain can be in any area of the body. As we mentioned earlier the brain can ‘learn’ to continue producing pain, so the pain may not only stay confined to the area of the cancer.

Visceral pain

Your viscera are your internal organs. Chronic visceral pain is defined as, “persistent or recurrent pain that originates from the internal organs of the head and neck region and the thoracic, abdominal, and pelvic cavities.”

Types of visceral pain include:

  • Irritable Bowel Syndrome (IBS): IBS is one of the most common visceral pain conditions. The International Foundation for Gastrointestinal Disorders states that IBS effects between 10% to 15% of the population worldwide. IBS affects the digestive system and can cause diarrhoea, constipation, bloating and stomach cramps among other symptoms.
  • Chronic primary pelvic pain syndrome (CPP): CPP causes pain in the pelvic area along with other symptoms such as digestive problems and problems with urination.

Available treatments

There are many treatments available which can be very effective at helping you manage, reduce and overcome chronic pain symptoms. The wide range of treatments available means that you can find something that works for you.

Psychological therapies

Psychological therapies are talking based therapies. Many are scientifically proven to help patients overcome chronic pain. You can access them through a referral from your doctor or specialist, privately or through an online source such as a pain management app like ours.

  • Cognitive Behavioural Therapy (CBT): CBT focuses on changing negative thoughts and behaviours. CBT can help you to introduce more positive thoughts and coping strategies to actively tackle your symptoms.
  • Acceptance and Commitment Therapy (ACT): ACT focuses on acceptance of your thoughts, feelings and symptoms, and commitment to proactive management strategies.
  • Graded Exposure Therapy: Through graded exposure therapy patients can gradually face their fears around chronic pain, tackling fear avoidance and increasing levels of functioning.
  • Graded Motor Imagery (GMI): GMI uses visualisation and imaged movements to gradually tackle situations which usually evoke pain. GMI can help you retrain your brain away from pain.
  • Biofeedback: Biofeedback utilizes medical equipment to help the patient become aware of their biological processes and how stress and relaxation can influence them. The patient can then learn to control these biological processes.
  • Mindfulness: Mindfulness is about being present in the moment, not holding onto worries or thinking about the past or future. This may involve meditation, breathing exercises and visualization. Mindfulness promotes a sense of relaxation and helps to break the stress and pain cycle.
  • Creative therapies: Creative therapies such as art therapy and music therapy, give the patient a creative outlet to express their feelings and in turn, learn to regulate their emotions more effectively. Other benefits of creative therapies include encouraging communication, providing a distraction and promoting social interaction.

Manual therapies

Manual therapies are those which involve movement which is either active (meaning done primarily by the patient while being guided) or passive (meaning the therapist does most of the work).

  • Physiotherapy: Physiotherapy (or physical therapy) typically involves both active and passive treatments. The therapist may guide you through exercises to increase your range of movement for example, or they may physically move and manipulate your body themselves. The aims of physiotherapy are to strengthen your body, improve your level of functioning and reduce pain levels.
  • Massage therapy: During massage therapy the therapist will use pressure and specific manipulation techniques to ease muscle tension and promote relaxation.
  • Hydrotherapy: Hydrotherapy involves doing specific exercises in warm water, to take the weight off your joints and ease pain while you increase your range of movement.
  • Acupuncture: During acupuncture very fine needles are inserted into specific areas of your body to encourage the release of the body’s natural pain relieving chemicals.
  • Chiropractic: Focusing on the back and spine, chiropractors will use firm movements and pressure to release tension. They may even physically move you into different positions to increase your range of flexibility and stretch your muscles.
  • Osteopathy: An osteopath physically manipulates areas of the body to strengthen muscles and release muscle tension. 

Pain clinics or pain management programmes

You are usually referred to a pain clinic by your doctor or specialist. During a pain clinic you will have the opportunity to see multiple specialists (including some of the types we have discussed) who will use a multidisciplinary approach to help treat your chronic pain.

Occupational therapy

An occupational therapist will help you to look at your day to day life and figure out how to practically increase your level of functioning and make life more manageable for you. This may involve them recommending mobility aids, advising specific ways to carry out tasks to minimize pain, and helping you to find a daily routine that works for you.

Medications

A range of medications are available, most of which require a prescription from your doctor. Some pain patients may find medications an effective way to manage their pain, while others may find little benefit.

  • Antidepressants: Antidepressants are thought to work by raising levels of certain chemicals in your brain, which is thought to reduce chronic pain.
  • Anticonvulsants: Anticonvulsants are thought to work by suppressing pain messages.
  • Steroids: Steroids prevent your body from producing the chemical which causes inflammation. This can help to reduce pain.
  • Painkillers: Over the counter pain killers may be helpful to some pain patients. Stronger painkillers may be prescribed by your doctor, including opioids (you might also have heard these called narcotics).

You can find more in depth guidance about your treatment options and how to effectively self-manage your pain from our comprehensive pain management guide, and our guide on living well despite your chronic pain.

Common misconceptions about chronic pain

Negative perceptions and misconceptions about chronic pain can have a significant negative impact on pain levels. Negative perceptions of pain reinforce to our brain that it should be producing pain and that these beliefs are true. These negative perceptions can also mean we’re less likely to manage our pain well.

These misconceptions may be instilled within you over the years. They can come from:

  • What medical professionals have told you
  • What loved ones say or believe (they may be trying to help you by being over protective, or may push you to do too much)
  • What society believes as a whole
  • What you have read from some online sources

Let’s take a look at some of the most common misconceptions and find out the truth!

Chronic pain is rare

While it can be all too easy to feel alone when you’re struggling with chronic pain, this is far from the truth! Chronic pain is extremely common. Looking at the statistics, this study shows that globally, “20% of adults suffer from pain globally and 10% are newly diagnosed with chronic pain each year.That means that one in every five people you come across are likely to have a form of chronic pain. So you can see, chronic pain is far from rare.

Chronic means forever

The definition of chronic is, “(of a disease) having long duration (opposed to acute).” Chronic means long term, but it does not mean permanent or forever. What doctors or society has told you may make you inclined to believe that recovery from chronic pain is not possible, but the opposite is true! You can recover from chronic pain! This recovery may look different for everyone. It may be reduction of symptoms, it may be well-managed symptoms, or it may be complete recovery, as in the case of our founder Sandip.

Chronic pain can’t be treated

When you are diagnosed with chronic pain, medical professionals may have told you that there isn’t any effective treatment or that you ‘just need to get on with it’. However this isn’t the case. There are plenty of scientifically proven treatments which can help you to tackle your chronic pain, and (as we mentioned above) help you to recover from it.

There’s no point in reaching out for help

Not all doctors are educated enough on chronic pain, so they may not always recommend effective treatments. This doesn’t mean you shouldn’t reach out for help! Some doctors may be very helpful. Even with those who are not, you can advocate for yourself or ask someone to help you advocate for the treatment you deserve. You can even access treatment  privately or online.

Chronic pain equals damage

Acute pain equals damage or an injury, but chronic pain does not. While it’s possible that the two occur together, chronic pain itself does not mean that your body is damaged. Through central sensitization pain can continue after an injury is completely healed, or without an injury being there at all!

Damage equals pain

Just as having chronic pain doesn’t mean your body is damaged, damage within your body doesn’t necessarily equal pain. As we age, our body ages on the inside too. Wear and tear is natural and doesn’t mean you will be in pain. Many people find out on scans for a completely separate medical issue, that they have had wear and tear within their joints for years for example, and have felt no pain at all!

You shouldn’t exercise if you have chronic pain

A lot of people believe that you shouldn’t exercise because you have chronic pain. Unlike acute pain, resting isn’t going to benefit your chronic pain. In fact being inactive can actually make your pain worse through deconditioning. When exercise is done in a safe and gradual way, it is highly beneficial for your health and can reduce your pain symptoms!

I can’t work if I have chronic pain

Just like with exercise, being active in your day to day life is a positive way to cope with your pain and reduce symptoms. You can work if you have chronic pain, particularly if it’s treated and well managed.

Pain is the only symptom

Many people, especially those from the outside looking in, may believe that pain is the only symptom of chronic pain. In fact chronic pain comes with many other symptoms and they are just as valid as the pain itself.

It’s ‘all in your head’

All pain is created in our brains, even acute pain. When we talk about the fact that our emotions can influence our pain, this is all based on science and doesn’t mean that your pain is ‘made up’ or any less valid.

I need to take painkillers if I have chronic pain

While painkillers may help some people, they can also cause side effects and may not be effective for other people. You don’t have to take painkillers if you have chronic pain. Your pain can be treated and reduced very effectively without them.

You can’t be ill, you don’t look sick

The majority of chronic pain conditions and symptoms are invisible. This doesn’t mean that they are any less valid. You can’t always tell what somebody is going through just by looking at them.

Key terms

These are terms you will likely find used a lot in information you read about chronic pain. You can use these key terms and their definitions as a reference point to refer back to.

  • Acute pain: Acute pain is ‘healthy pain’. It’s the body’s alarm system to protect you from harm and let you know when something is wrong. Acute pain can be defined as being: “provoked by a specific disease or injury, serves a useful biologic purpose, is associated with skeletal muscle spasm and sympathetic nervous system activation, and is self-limited.”
  • Chronic pain: Chronic pain is long term pain which lasts longer than 3 to 6 months.
  • Pain messages: These are messages which are sent between your brain and your nervous system, controlling when you feel pain.
  • A flare: An increase in your symptoms.
  • Hypervigilance: A state of high alert. Being constantly aware and on the lookout for threats.
  • Catastrophizing: Excessively worrying about pain or anticipated pain, in a way that is detrimental to your day to day life.
  • Fear avoidance: Avoiding activity because you fear it will worsen your pain.
  • Central sensitization: An overactive nervous system which perpetuates the pain cycle.
  • Nociception: Your nervous system’s detection of potentially harmful stimuli. Nociception can be described as: “the detection of noxious stimuli, is a protective process that helps prevent injury by generating both a reflex withdrawal from the stimulus and as a sensation so unpleasant that it results in complex behavioral strategies to avoid further contact with such stimuli.”
  • Maladaptive: An unhelpful or harmful behaviour.
  • Adaptive: A helpful or positive behaviour.
  • Hyperalgesia: An increased sensitivity to painful stimuli.  
  • Allodynia: Experiencing pain from stimuli which usually wouldn’t cause pain.
  • Stress and pain cycle: Referring to how stress causes pain and pain causes stress, producing a cycle within which one perpetuates the other.
  • The mind body connection: Our minds and bodies are connected and can influence one another. Physical health can influence mental health, and mental health can influence physical health.

References

  • Treede, R. D., Rief, W., Barke, A., Aziz, Q., et al, (2015). “A classification of chronic pain for ICD-11”. Pain, 156(6), 1003–1007. 
  • National Institute of Biomedical Imaging and Bioengineering, (2020), “Computed Tomography (CT)”. National Institutes of Health
  • Nicholas, Michael & Vlaeyen, Johannes & Rief, Winfried & Barke, et al, (2018). “The IASP classification of chronic pain for ICD-11: chronic primary pain.” Pain. 160. 28 – 37. 
  • Naleschinski D, Baron R., (2010), “Complex regional pain syndrome type I: neuropathic or not?” Curr Pain Headache Rep. 2010 Jun;14(3):196-202.
  • James C. Watson, (2020), “Complex Regional Pain Syndrome (CRPS)”. MSD MANUAL
    Professional Version
  • Goldberg DS, McGee SJ., (2011), “Pain as a global public health priority.” BMC Public Health. 2011 Oct 6;11:770
  • Grichnik KP, Ferrante FM., (1991), “The difference between acute and chronic pain.” Mt Sinai J Med. 1991 May;58(3):217-20.
  • Latremoliere, A., & Woolf, C. J. (2009). “Central sensitization: a generator of pain hypersensitivity by central neural plasticity.” The journal of pain : official journal of the American Pain Society, 10(9), 895–926. 
  • Dictionary.com LLC, (2020), “Chronic”. 
  • International Foundation for Gastrointestinal Disorders, (2016), “Facts About IBS”. 
  • NHS, (2019), “Trigeminal neuralgia”. 
  • NHS, (2019), “Spondylolisthesis”. 
  • NHS, (2019), “Ankylosing spondylitis”.

Please note: This article is made available for educational purposes only, not to provide personal medical advice.

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