PUBLIC HEALTH ASPECTS OF PAIN DISORDERS

Pain — acute and chronic — is a ubiquitous experience and it is also a major public health problem that poses signifi cant challenges to health professionals involved in its treatment. Reliable data about the prevalence and incidence of pain, however, are limited, with available studies being based on either regional surveys of a broad spectrum of painful disorders, or specifi c pain states.

In a collaborative study of pain in a primary care setting, WHO revealed that persistent pain affl icted between 5.3% and 33% of individuals resident in both developing and developed countries. The lowest frequency was reported in Nigeria and the highest in Santiago, Chile. The study revealed that persistent pain was associated with depression, which affected the quality of life and reduced the level of daily activity of the sufferers . It was concluded that the essential need to work and to earn income might be a reason why many people in developing countries tolerate pain rather than reporting to doctors or hospitals. Therefore, lack of an adequate social and health-care support network, cost implications and job security must infl uence the extent to which people living in developing countries and suffer pain fail to seek help.

A detailed study of the prevalence, severity, treatment and social impact of chronic pain in 15 European countries was carried out recently . The prevalence of chronic pain ranged between 12% and 30%, fi gures similar to those in the WHO study. The most common sites for pain were the head and neck, knees and lower back. Of the respondents, 25% had head or neck pains (migraine headaches, 4%; nerve injury from whiplash injuries, 4%). Although back pain may have a neurological cause, the likelihood was that in the great majority pain was the result of musculoskeletal disorders or back strain. The authors concluded that one in fi ve Europeans suffer from chronic pain which is of moderate severity in two thirds and severe in the remainder. The study also reveals that, in the opinion of 40% of the respondents, their pain had not been treated satisfactorily and 20% reported that they were depressed. In economic terms, 61% were less able or unable to work outside their homes, 19% had lost their jobs because of pain and another 13% had changed their jobs for the same reason.

A large-scale survey in Australia of just over 17 000 adults with pain daily for at least three months (chronic pain) yielded a prevalence rate of 18.5%; in a comparable survey in Denmark, a prevalence rate of 19% was obtained . It is therefore evident from the three surveys that a prevalence rate for chronic pain of 18–20% is to be expected in adult populations selected at random from developed countries. Unfortunately, these fi gures do not give any detail about pain arising from the nervous system, except for the information about head and neck pain in the European survey.

Certain neurological disorders causing pain have been examined in terms of the incidence of pain. For example Kurtzke estimated that the annual incidence of herpes zoster infection in the United States was 400 per 100 000 of the population. A study of the incidence of post-herpetic neuralgia in 1982 revealed a fi gure of 40 per 100 000 . Further information from Bowsher indicated that the number of individuals with post-herpetic neuralgia increases with age so that 40% of people over 80 years of age who acquire acute herpes zoster will suffer from chronic postherpetic neuralgia. In populations in which ever greater numbers are living to 80 years and more, there is likely to be a signifi cant increase in individuals suffering from post-herpetic neuralgia.

The earlier study by Ragozzino et al. gave fi gures for the anatomical distribution of the neuralgia that was present in 56% in the thoracic region, 13% in the face and 13% in the lumbar regions; 11% had pain in the cervical region. One third of patients with multiple sclerosis develop neuropathic pain states, of whom trigeminal neuralgia occurs in 5%, and another one third develop other forms of chronic pain . There is an increase in the incidence of trigeminal neuralgia in patients with cancer and other diseases that impair the immunological systems.

It is signifi cant that one third of cancer patients have a neuropathic component to their pain as do a similar proportion of patients with prolonged low back pain .

It should be noted that stump pain arises from a severed nerve in the limb and may be caused by a local neuroma or by tethering of the severed nerve to local tissues. In either case the pain is of the peripheral neuropathic type. In contrast, phantom limb pain is central neuropathic pain and more diffi cult to treat.

Central stroke pain is defi ned as neuropathic pain that follows an unequivocal episode of stroke. It is associated with partial sensory loss in all but a few cases. A prospective study by Andersen et al. revealed a one-year incidence of 8%, with symptoms being severe in 5% and mild in 3%. For most patients the pain develops gradually during the fi rst month but delays of many months have been recorded. The pain is incapacitating, distressing and often even more so than other symptoms.

Headache disorders have also been the subject of intensive epidemiological research .

Poor relief of acute pain is a recognized risk factor for the development of chronic pain after various forms of surgery, for example herniotomy, mastectomy, thoracotomy, dental surgery and other forms of trauma. In part, this is the result of nerve injury which presents as acute neuropathic pain in 1–3% of patients. The majority of such patients experience persistent pain one year after the causative event, indicating that acute neuropathic pain is a very defi nite risk factor for chronic pain. Prompt treatment of early nerve pain is therefore important .

Hernia repair is followed by moderate to severe pain in 12% of patients one year postoperatively and is of the somatic or neuropathic type . Breast surgery of various types gives rise to the experience of phantom breast and pain with or without a phantom.

Information about the incidence and prevalence of pain generally, and neurologically related pain in particular, is almost totally lacking for developing countries, although there is no reason to believe that conditions that give rise to pain such as stroke, multiple sclerosis, various forms of headache and other disorders vary in nature. There may well be differences, however, in the extent to which some disorders are present, for example multiple sclerosis is less common in developing countries, whereas others are not encountered in the Western world, such as certain forms of poisoning by neurotoxins from foods, and leprosy which is a cause of neuropathic pain.

HIV/AIDS is a major cause of neuropathic pain in the later stages of the disease: 70% of AIDS sufferers develop this form of pain, which is severe and comparable with the severe pain experienced in cases of advanced cancer. The incidence of severe pain must, therefore, be high in countries where AIDS is a major health problem.

The figures quoted in this section show that a signifi cant number of individuals suffer from chronic and incapacitating pain as a result of diseases of the nervous system, or as a result of damage to peripheral nerves at the time of surgery and other forms of trauma. The nature of the pain, which is often neuropathic in type, means that the sufferer has a disabling condition that in time may be primarily the result of pain, which is diffi cult to relieve. As such, it poses a signifi cant health problem in terms of its personal, social and economic consequences.