Pain is a private percept that arises in a conscious brain, typically in response to a noxious provoking stimulus, but sometimes in the absence of a stimulus. The relation of the percept to the stimulus is variable, and depends on the individual's prior expectations and beliefs, and on his/her cognitive and emotional state, not just on the nature of the stimulus itself. The nervous system may react to noxious stimuli with autonomic changes (e.g. in blood pressure), and even with adaptive behavioral responses, in the absence of a conscious pain percept. Likewise, there are circumstances in which the presence of pain is ambiguous, such as when the individual is unable to report on his/her conscious percept, or with reference to animals. In these situations, the word "nociception" is used instead of the word "pain" to express that the nervous system has detected the noxious stimulus without necessarily implying that a pain percept was evoked.

The European Pain Federation (EFIC) has declared pain as a major health problem, a disease in its own right: "Pain is a major healthcare problem in Europe. Although acute pain may reasonably be considered a symptom of disease or injury, chronic and recurrent pain is a specific healthcare problem, a disease in its own right".


Acute pain, such as that following trauma or surgery, constitutes a signal to a conscious brain about the presence of noxious stimuli and/or ongoing tissue damage. This acute pain signal is useful and adaptive, warning the individual of danger and the need to escape or seek help. Acute pain is a direct outcome of the noxious event, and is reasonably classified as a symptom of underlying tissue damage or disease.  However, in many patients pain persists long after its usefulness as an alarm signal has passed, and indeed, often long after the tissue damage has healed. Chronic pain in these patients is probably not directly related to their initial injury or disease condition, but rather to secondary changes including ones that occur in the pain detection system itself.

In addition to being due to different physiological mechanisms than acute pain, chronic pain often sets the stage for the emergence of a complex set of physical and psychosocial changes that are an integral part of the chronic pain problem and that add greatly to the burden of the pain patient. These include:

1. immobility and consequent wasting of muscle, joints etc.
2. depression of the immune system and increased susceptibility to disease
3. disturbed sleep
4. poor appetite and nutrition
5. dependence on medication
6. over-dependence on family and other caregivers
7. overuse and inappropriate use of professional healthcare systems
8. poor performance on the job or inability to work, disability
9. isolation from society and family, turning inwards
10. anxiety, fear
11. bitterness, frustration, depression, suicide

Prevalence of chronic pain

Although comprehensive epidemiological data for the European Union are not available, chronic pain is clearly a very widespread condition. Several recent community-based surveys, for example, found that about 50% of adults sampled suffered from one or more types of pain at any given point in time. In a substantial proportion of those surveyed, the pain was both chronic and severe -the numbers increasing considerably in older age groups.  The most widespread chronic pain conditions, low back pain, arthritis and recurrent headache (including migraine) are so common that they are often seen as a normal and unavoidable part of life. Although few people die of pain, many die in pain, and even more live in pain.


Social costs of chronic pain
While acute pain is by definition a brief and self-limiting process, chronic pain comes to dominate the life and concerns of the patient, and often also family, friends and other caregivers. In addition to the severe erosion in quality of life of the pain sufferer and those around him/her, chronic pain imposes severe financial burdens on many levels. These include:

1. costs of healthcare services and medication
2. job absenteeism and disruption in the workplace
3. loss of income
4. non-productivity in the economy and in the home
5. financial burden on family, friends and employers
6. worker compensation costs and welfare payments

Authoritative sources place the overall financial costs of chronic pain to society in the same range as cancer and cardiovascular disease.


Detailed information on this subject is available from the following sources:

1. Wall P.D. and R. Melzack (eds.) Textbook on Pain, 6th Edition. Edited  By Stephen McMahon, FMedSci, FSB, Martin Koltzenburg, MD, FRCP, Irene Tracey, MA (Oxon.), PhD, FRCA and Dennis C. Turk, PhD. Saunders 2013, 1184pp.
2. J. D. Loeser (ed.) Bonica's Management of Pain, Third Edition, Lea and Febiger, 2000. (Harcourt). New edition will be released on October 13, 2018.
3. Practical Management of Pain, Fifth Edition, Honorio Benzon James Rathmel Christopher L. Wu Dennis Turk Charles Argoff Robert Hurley.Mosby 2013.
4. Orofacial pain and Headache. Edited by Yair Sharav and Rafael Benoliel. Chicago Quintessence Publishing Co, Inc, [2015]
5. Relieving Pain in America: A Blueprint for Transforming Prevention, Care, Education, and Research. Institute of Medicine. 2011.
6. Raj's Practical Management of Pain. 4th Edition. Authors: Honorio Benzon James Rathmell Christopher L. Wu Dennis Turk Charles Argoff. Mosby 2008,1344pp.