Definition

Pain is a term generally  understood by all and as a matter of fact, every individual regardless of age, sex, race, economic and social status must have at one time in their lifetime experienced pain.

While the definition and description of pain is always relative, subjective and vary from one person to another, the International Association for the Study of Pain defined it as an unpleasant sensory and emotional experience associated with actual or potential tissue damage. In medical diagnosis, pain is regarded as a symptom of an underlying condition and it can be helpful in diagnosing a problem. Without pain, it may be difficult to realise that one has a medical problem that needs treatment. In plain terms, pain as a sensation can be regarded as a protective one as it motivates the individual to withdraw from damaging situations, to protect a damaged body part while it heals, and to avoid similar experiences in the future. In most cases, it is what prompt people to seek treatment from a physician and it is the reason why most people seek medical attention in most developed countries.

How common is Pain?

According to Goldberg and McGee (2011), the global prevalence of pain is 20% and 10% are being diagnosed with chronic pain every year. This implies that one out of every five individuals suffers from pain and one out of ten is diagnosed of chronic pain yearly. The prevalence ranges from one country to another. The prevalence in UK was reported to be 43.5% (4 of every 10 persons) by Fayaz et. al. (2016) and that in Canada was 20% (The Canadian Pain Society, 2014) and despite this, pain research is grossly under-funded in Canada (Lynch, 2009).

Types and classification of pain

There are various types of pain and classification of pain depends on the criteria used. Pain can be classified based on where it is localized in the body (i.e. where the pain is felt), duration (how long the pain is felt), the cause of the pain and classifications may overlap. However, for the sake of clarity, the following types or classes of pain are considered in this write-up:

Classification by duration – Acute Pain and Chronic Pain

One of the several ways to categorize pain is to separate it into acute and chronic. Acute pain in nearly all cases begins suddenly, usually sharp in quality and it is self-limited (i.e. has a limited duration). It’s frequently caused by damage to tissues such as bone, muscle, or organs, and the onset is often accompanied by anxiety or emotional distress. The pain normally stops as soon as the damaged tissue heals. Acute pain might be caused by many events or circumstances, including but not limited to surgery, broken bones, dental work, burns or cuts and labour and childbirth.

Acute pain might be mild and last just a moment, or it might be severe and last for weeks or months. In most cases, it does not last longer than six months, and it disappears when the underlying cause of pain has been treated or has healed. Unrelieved acute pain, however, might lead to chronic pain.

Chronic pain on the other hand lasts longer than acute pain and is generally somewhat resistant to medical treatment. It is usually associated with long-term illnesses, such as osteoarthritis and it persists even after tissue healing is complete. In some cases, such as with fibromyalgia, it’s one of the defining characteristic of the disease. Chronic pain can be the result of damaged tissue, but very often is attributable to nerve damage.

In chronic pain situations, pain signals remain active in the nervous system for weeks, months or years. Physical effects include tense muscles, limited mobility, a lack of energy, and changes in appetite. Emotional effects include depression, anger, anxiety, and fear of re-injury. Such a fear might hinder a person’s ability to return to normal work or leisure activities. Common chronic pain complaints include, headache, low back pain, cancer pain, arthritis pain, neurogenic pain (pain resulting from damage to nerves), psychogenic pain (pain not due to past disease or injury or any visible sign of damage inside) etc.

Both acute and chronic pain can be debilitating, and both can affect and be affected by a person’s state of mind. But the nature of chronic pain – the fact that it’s ongoing and in some cases seems almost constant – makes the person who has it more susceptible to psychological consequences such as depression and anxiety. At the same time, psychological distress can amplify the pain.

Chronic pain might have originated with an initial trauma/injury or infection, or there might be an ongoing cause of pain. However, some people suffer chronic pain in the absence of any past injury or evidence of body damage.

Classification by cause – Nociceptive Pain and Neuropathic Pain

Pain can also be classified according to the kind of damage that causes it. The two main categories are pain caused by tissue damage, also called nociceptive pain, and pain caused by nerve damage, also called neuropathic pain. A third category is psychogenic pain, which is pain that is affected by psychological factors. Psychogenic pain most often has a physical origin either in tissue damage or nerve damage, but the pain caused by that damage is increased or prolonged by such factors as fear, depression, stress, or anxiety. In some cases, pain originates from a psychological condition.

Pain Caused by Tissue Damage (Nociceptive pain)

Most pain comes from tissue damage. The pain stems from an injury to the body’s tissues. The injury can be to a bone, soft tissues, or organs. The injury to body tissue can come from a disease such as cancer. Or it can come from physical injury such as a cut or a broken bone. These damages are picked up by specialized receptors or nerve endings called nociceptors (or pain receptors) and relayed to the brain and spinal cord for interpretation and response.

The pain experience may be an ache, a sharp stabbing, or a throbbing. It could come and go, or it could be constant. The pain may worsen due to muscle movement and sometimes breathing deeply can intensify it. Pain from tissue damage can be acute or chronic and certain medical treatments, such as radiation for cancer, can also cause tissue damage that result in pain.

Nociceptive pain can further be divided into somatic and visceral pain. Somatic pain originates from the skin and the deep tissues while visceral pain comes from internal organs. While somatic pain are easily localized (i.e. the place where they originate are easily known and identified) in the body, visceral pain is not. This is because most internal organs do not have much pain receptors (the brain for example has no pain receptors) and pains originating from them are felt in other remote parts of the body. This is called referred pain. For example, pain originating from the heart is usually felt in the region between the chest and the shoulder (angina pectoris – popularly called chest pain).

Pain Caused by Nerve Damage (Neuropathic pain)

Nerves function like electric cables transmitting signals, including pain signals, to and from the brain. Damage to nerves can interfere with the way those signals are transmitted and cause pain signals that are abnormal. For instance, you may feel a burning sensation even though no heat is being applied to the area that burns.

Nerves can be damaged by diseases such as diabetes, or they can be damaged by trauma. Certain chemotherapy drugs may cause nerve damage. Nerves can also be damaged as a result of stroke or an HIV infection, among other causes. The pain that comes from nerve damage could be the result of damage to the central nervous system (CNS), which includes the brain and spinal cord. Or it could result from damage to peripheral nerves, those nerves in the rest of the body that send signals to the CNS.

The pain caused by nerve damage, is often described as burning or prickling. Some people describe it as an electrical shock. Others describe it as pins and needles or as a stabbing sensation. Some people with nerve damage are often hypersensitive to temperature and to touch. Just a light touch, such as the touch of a bed sheet can set off the pain.

Treatment and management of pain

Treatment and management of pain usually depend on the type. The therapy of acute pain is aimed at treating the underlying cause and interrupting the nociceptive signals while that of chronic pain must rely on a multidisciplinary approach and should involve more than one therapeutic modality. Various treatment and management options for chronic pain which is of great public health importance in recent time will be discussed at length in subsequent publications on this platform. Acute pain can however be treated by resting the affected part of the body, application of heat or ice, use of non-steroidal anti-inflammatory drugs (NSAIDs) such as aspirin, ibuprofen, or naproxen; or acetaminophen, physical therapy, exercise, bioelectric therapy (using local electrical stimulation to moderate pain), opioid (narcotic) medications (such as codeine or morphine) etc. The treatment of chronic pain on the other hand is more challenging and may involve several combinations. This may include the use pain medicines (such as pain pills, topical analgesics, cooling sprays and injections), physical therapy and complementary therapies (e.g. acupuncture, biofeedback, yoga etc) and surgery, such as intrathecal drug delivery and spinal cord stimulation (which is only considered after other treatments have failed or when medically necessary.

Recently, medical marijuana and platelet rich plasma (PRP) have shown promising results in the treatment and management of chronic pain. This will be discussed at length in subsequent publications.

For more information or to read more, please visit the following web addresses:

  • http://www.spine-health.com
  • http://www.iasp-pain.org/
  • http://www.britishpainsociety.org/
  • http://www.patient.co.uk/directory/pain
  • https://medlineplus.gov/pain
  • http://www.medicinenet.com/script/main/art.asp?articlekey=4723
  • http://www.dorsetpain.org.uk/Docs/Classification%20of%20pain.pdf
  • http://www.physio-pedia.com/Referred_Pain
  • https://www.verywell.com/what-is-nociceptive-pain-2564615
  • http://www.painfoundation.org
  • http://www.abpm.org
  • http://www.asahq.org
  • http://jamanetwork.com/journals/jama/fullarticle/194526
  • http://www.painscience.com

References

Assessment of pain (2008). Br J Anaesth. 101(1):17–24.

Debono DJ., Hoeksema LJ., Hobbs RD., 2013. “Caring for Patients with Chronic Pain: Pearls and Pitfalls”. Journal of the American Osteopathic Association. 113(8): 620–627

Goldberg DS and McGee SJ., 2011. Pain as a global public health priority. BMC Public Health 2011(11): 770.

Grichnik KP., Ferrante FM., 1991. The difference between acute and chronic pain. Mt Sinai J Med.  58(3): 217-20.

International Association for the Study of Pain (2015). Pain Definitions. Derived from The need of a taxonomy. Pain. 1979; 6(3):247–8.

Lynch ME., Schopflocher D., Taenzer P and Sinclair C., 2009. Research Funding for pain in Canada. Pain Res Manage 14:113-115.

Schopflocher D., Taenzer P., and Jovey R., 2011. The prevalence of chronic pain in Canada. Res Manage 16(6): 445-450

Taxonomy and classification of pain. The Handbook of Chronic Pain. Nova Biomedical Books; 2007. ISBN 1-60021-044-9.

The neurobiology of pain: Symposium of the Northern Neurobiology Group, held at Leeds on 18 April 1983. Manchester: Manchester University Press; 1984. ISBN 0-7190-0996-0. Cutaneous nociceptors. p. 106.

What should be the core outcomes in chronic pain clinical trials?. Arthritis Research & Therapy. 2004;6(4):151–4

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