A new book explains the differences between acute pain, chronic pain, and chronic pain syndrome

Pain that is physiological is called acute pain. Usually, any pain starts off as acute pain; but when it persists for over twelve weeks it is termed as chronic pain. In chronic pain, physical pain alone does not define it as other perhaps more dominant, psychological and social factors compound it. Some of these psychosocial problems could be poor sleep, reduced performance at work, loss of job or loss of status in the family and society. All these factors are potentially stress-inducing. When the person is unable to cope, it leads to stress, nervousness, anxiety and often depression. Since the pain pathways and the limbic system in the brain are functionally connected and activated together, any changes in the mood state trigger the nervous system. As pain is also a nerve-related phenomenon, the activated neurons cause an increase in the perception of pain. This forms a vicious cycle as chronic pain begets psychosocial difficulties and they, in turn, beget more pain. Hence, when the psychological symptoms overshadow the physical symptoms, it is called chronic pain syndrome. To rephrase it, the mind starts to dominate over the body. In such patients, it is important to address the mind as much as we address the body, in order to relieve the suffering. And for that, a multidisciplinary approach to management is often required. In contrast to acute pain, pain in patients with chronic pain and chronic pain syndrome can become a double-edged sword when pain no longer has an adaptive and protective function but it, instead, becomes a disease in itself that causes disability and long-lasting suffering.

Acute pain

Let us now try and understand the pain that is useful and protective (acute pain) and then see how pain ceases to be protective and instead becomes a disease (chronic pain).

As mentioned earlier, acute or physiological pain has both an adaptive and a protective function. While the adaptive function enables us to react appropriately to a threatening environment, the protective function warns of some impending tissue damage, injury or disease. In fact, this type of pain is needed for our very survival. It is termed physiological (‘physio’ means nature or natural) because it is normal to have this kind of pain and, in fact, not having it can be abnormal and even harmful. Congenital insensitivity to pain is a genetic disorder, which means a person is born with the inability to perceive physical pain and the absence of this protective sensation can adversely affect the lifespan of these individuals. This is because pain not only induces a reflex withdrawal from the injurious stimulus, but also initiates certain behavioural strategies that protect a person from further injury. An example would be the withdrawal of the hand (reflex behaviour) when it is too close to fire (injurious stimulus). Thus, it is natural or physiological to experience pain after an injury, inflammation or surgery. There is also a stress response associated with acute pain depending on its severity, which is the fright, fight and flight response. This is termed as the autonomic response and it manifests as sweating, fast pulse rate, rapid breathing, raised blood pressure and dilatation of the pupils.

Acute pain lasts for only a short duration or till such time as the injury or tissue damage is present. It can affect our musculoskeletal system (somatic pain) or it can affect our internal organs or viscera (visceral pain). Some examples of acute pain are sprains, fractures, burns, surgery, cancer, arthritis or due to inflammation of internal organs like appendix, gall bladder or the urinary system, as in renal stones. Healing or resolution of the problem usually results in the pain abating and this time period is usually less than six weeks or a maximum of twelve weeks.

Chronic pain

Now, let us see what happens in chronic pain. Pain is considered chronic when it has lasted for more than twelve weeks, persisting long after the healing period of an injury or inflammation is over. Although initially it might have had a beneficial function, but when it persists, it becomes a disease in itself causing distress and suffering and, hence, is termed as pathological pain (‘pathos’ means suffering). It has also been termed as dysfunctional pain as it serves no beneficial function, but rather causes impairment in functionality of the person and adversely affects the quality of life. Psychologically speaking, chronic pain is a major stressor to the patient and consequently to the family, as there may be fears related to the uncertainty of regaining adequate functionality. The fear of dependency at all levels – physical, psychological and financial – may be present as an unwelcome appendage.

The same conditions that caused physiological pain can lead to or progress to pathological pain or chronic pain, except that while acute pain is largely due to tissue damage (nociceptive), in chronic pain multiple factors could be contributory and tissue injury may not always be present. In fact, in some cases of chronic pain, there may not be any underlying physical abnormality at all.

In contrast to acute pain, chronic pain tends to be more resistant to treatment. The prevalence of chronic pain worldwide is 20 per cent and is a cause of distress, disability and economic burden. It is indeed heartening that for the first time in 2019, the classification of chronic pain has been included in WHO’s ICD-11.6 According to this classification there are seven groups of chronic pain, which broadly come under two major categories. These are as follows:

• Chronic primary pain

• Chronic secondary pain – Chronic cancer pain; chronic post-traumatic or post-surgical pain; chronic neuropathic pain; chronic headache and orofacial pain; chronic visceral pain; chronic musculoskeletal pain

In chronic primary pain, there is no other primary disease or disorder that could possibly contribute to the pain. This category includes psychological pain and widespread pain, as in fibromyalgia. Chronic secondary pain, on the other hand, is due to an underlying disease or conditions such as cancer, trauma or surgery, dysfunction of the nervous system, headaches and facial pains, musculoskeletal disorders or diseases in the organs of the body (visceral pain).

Chronic pain syndrome

Chronic pain syndrome is a little different from chronic pain and was delineated as a separate entity only in 1987. While in chronic pain, pain is the predominant symptom, in chronic pain syndrome, psychological symptoms are more prominent as compared to the physical symptoms of pain. Pain must be present for at least six months for it to be diagnosed as chronic pain syndrome. This condition is seen in approximately 25 per cent of patients with chronic pain. The psychological symptoms include depression, anxiety and mood-related changes such as lack of sleep, anger, frustration, loss of sexual desire, fatigue, irritability, guilt, substance abuse, marriage and family problems, job loss and even suicidal ideation. These symptoms become inextricably intertwined with pain and, in fact, become more dominant. So, what began as a simple tissue injury, gets affected by various physical, genetic, environmental and psychological factors – spiralling into a chronic pain condition where the psychological and social ramifications overshadow the physical symptoms.

Some of the common chronic pain conditions that lead to chronic pain syndrome are musculoskeletal disorders like various types of arthritis; neurological disorders like neuralgias (trigeminal, post-herpetic), migraine, cervical disc disease, degenerative spine disease; urological disorders like interstitial cystitis (inflammation of the urinary bladder), reproductive tract disease (endometriosis) and fibromyalgia. Other conditions such as treatment of cancer and chronic post-surgical pain are also perpetrators of chronic pain syndrome.

Psychological disorders that may make the person prone to develop chronic pain syndrome include major depression, dysthymia, anxiety disorders, some personality disorders and somatisation disorders.

Excerpted with permission from Managing Chronic Pain, Mary Abraham and Vandana V Prakash, HarperCollins India.