The science of chronic pain

What is Chronic Pain?

Imagine waking up every day wondering if you are going to have a ‘good pain day' or a ‘bad pain day'? That is the harsh reality of those who suffer the perils of chronic pain. Chronic pain is a condition where pain persists beyond expected healing times of an illness or injury.

Under normal conditions, pain serves a short-term protective function that resolves with healing. However, when pain persists for three or more months, it moves into the realm of a condition that not only has no benefit, but becomes something itself that needs to be treated and managed.

Prevalence and burden of chronic pain

Chronic pain affects one-in-five Australians, at a cost of $40 billion a year—a burden that significantly outweighs that of cancer or diabetes. It is also a leading cause of disability and social exclusion.

Despite the prevalence, the biology of chronic pain is still unclear.

Like most ‘invisible’ illnesses, chronic pain does not get the recognition it deserves. Because every patient is different and the type, amount and frequency of pain is unique to the individual, the condition can be difficult to understand and manage. The interplay between physical sensation and the perception of pain is an individual experience and difficult to convey to someone not experiencing the same thing.

Clinical Features of Chronic Pain

Chronic pain is a biopsychosocial experience, having physiological, emotional and psychological components.

Physiologically, pain perception can increase heart rate, blood pressure and respiration rate. These physiological stressors can feed into a vicious cycle that progressively intensifies pain signalling at various levels of our nervous system.

Chronic pain can also trigger a complex array of emotions like shame, fear, guilt, anxiety and worthlessness. These negative feelings have a propensity to exacerbate pain and impede recovery, leading to behavioural changes such as avoidance, isolation and functional disability.

Furthermore, differences in individual circumstances, attitudes, mood and mental health status can either facilitate recovery or prolong it.

The causes of chronic pain can be difficult to accurately interpret and identify. Chronic pain may be best treated independently and recognised as a disease in its own right. Common co-existing conditions such as depression, anxiety, compromised immune function, fatigue, sleep disturbances, tumour growth and even suicide, add another layer of complexity to the management of chronic pain, and can further reduce quality of life.  

Types of Chronic Pain

Chronic pain can be continuous or episodic. It comes in many different forms making it extremely difficult to classify. Sometimes chronic pain directly relates to specific illnesses like chronic inflammatory disease or cancer. Other times it has no clear identifiable biological origin. More commonly though, chronic pain arises from nervous system dysfunction.

Recently the World Health Organisation divided chronic pain into seven categories to encompass the most common clinically relevant chronic pain disorders (Treede et al., 2015). These are listed below.

  1. Chronic primary pain (e.g. fibromyalgia, irritable bowel syndrome)
  2. Chronic cancer pain (caused by cancer or cancer treatment)
  3. Chronic post-surgical or post-traumatic pain (persisting for greater than 3 months after tissue damage)
  4. Chronic neuropathic pain (caused by nervous system lesion/disease)
  5. Chronic headache and orofacial pain (idiopathic or symptomatic)
  6. Chronic visceral pain (caused by inflammation, ischemia, thrombosis, distension, obstruction, compression around internal organs)
  7. Chronic musculoskeletal pain (pain arising from bones, muscles, joints and related soft tissues)

When pain signals don’t turn off – a disease of the nervous system

Chronic pain transpires from malfunctions in how the body regulates pain. This likely happens by reducing our pain threshold (making it easier to feel pain), by ramping up pain signalling pathways, or putting the brakes on pathways that inhibit pain signals.

Physical and psychological stressors in injury and disease can actually change the way neurons connect and communicate with each other. For instance, when pain pathways are overactivated from chronic inflammation, poorly managed acute pain, or complicated, prolonged or abnormal healing processes, sometimes persistent changes can occur to the way neurons function.

In some cases, these changes can cause someone to perceive pain when no painful stimuli has occurred—this is called allodynia.

Under normal conditions, nociceptors are responsible for detecting 'noxious' or painful stimuli. Following injury, trauma or illness, nociceptors that have been damaged or lost can grow back abnormally and produce erratic signals. Sensitisation of these receptors can lead to ongoing pain being experienced.  

Such continuous firing of peripheral nociceptors can cause persistent changes in the brain and spinal cord that can result in irregular processing of  spread pain stimuli independently of nociceptors, a process called central sensitisation.

Put simply, chronic pain can result from rogue signalling anywhere along pain pathways, causing an exaggerated, perpetual pain response known as hyperalgesia.

Challenges in Treating Chronic Pain

The prognosis for people who have chronic pain can be considerably varied.  Treatments for chronic pain are complicated by different psychological and emotional symptoms and contexts. 

Even among individuals with seemingly identical pathology, there is no one-size fits all treatment process. Rather, the treatment of chronic pain demands a holistic, multidisciplinary, patient-centered approach that combines pharmacological and non-pharmacological interventions.

Current medicines for chronic pain typically deliver a 50 percent reduction in pain for about one-third of patients. This leaves a significant portion of people suffering incapacitating pain on a daily basis.

Paracetamol and non-steroidal anti-inflammatory drugs like ibuprofen are commonly used to alleviate mild to moderate chronic pain. However, neither of these are effective in actioning a pain-free life.

Doctors may also prescribe opioids for the treatment of chronic pain. A major downfall of this class of painkillers is that they can be addictive and overdose can be lethal. Also, the analgesic effects of opioids diminish over time due to tolerance, feeding into a dangerous cycle of overuse. Therefore, clinicians are reluctant to use opioids long-term, and the undertreatment of pain becomes the safest option.

Psychotherapy, relaxation techniques and exercise, have also proven effective in the management of chronic pain.

Current options for chronic pain management are far from ideal. That is why scientists from the Centre for Pain Research at the Institute for Molecular Bioscience (IMB) are working to understand the complex pathophysiological mechanisms of chronic pain and identify safer, more effective treatments that integrate the disciplines of medicine and allied health.


Author: Dr Falak Helwani​