Visceral pain: the importance of pain management services

Visceral pain, the pain we feel when our internal organs are inflamed, diseased, damaged or injured, is by far the most common type of pain. All of us will have experienced pain emanating from our internal organs, from the mild discomfort of indigestion to the agony of renal colic. Although many types of visceral pain are particularly prevalent in women, for both men and women pain of internal origin is one of the most common reasons for consulting a doctor.

Visceral pain is unique; it is different to somatic pain. Visceral pain is not evoked from all viscera, not always linked to visceral injury, referred to other locations, diffuse and poorly localized and accompanied by motor and autonomic reflexes.

The mechanism of visceral pain is still less understood than that of somatic pain, in spite of ground-breaking research from eminent basic scientists clarifying the specific peripheral and central mechanisms involved.^1–3 Clinical models for visceral pain have been difficult to study. However, the recent elegant research from Giamberardino’s group has prompted greater awareness of visceral hyperalgesia, visceral–somatic hyperalgesia and viscero–visceral hyperalgesia and the importance of these phenomena in the routine clinical management of patients with visceral pain.⁴

Epidemiological data highlight the wide prevalence of visceral pain. Surveys have shown prevalence rates among adults of 25% for intermittent abdominal pain, 20% for chest pain and 16–24% for pelvic pain in women.

Chest, abdominal and pelvic pain can be indications of specific underlying disease, but in many sufferers all diagnostic tests are either normal or negative.

Abdominal pain for which no definite explanation could be found was established as the tenth most common cause of hospital admission for any reason in men and the sixth most common cause in women. Up to 67% of consecutive admissions to a teaching hospital surgical ward are for ‘non-specific’ abdominal pain.⁵

It has been estimated that non-specific abdominal pain costs the UK over £100 million each year.

The serious nature of coronary artery disease means that chest pain is considered to be cardiac in origin until proved otherwise, and is a common reason for emergency department and acute medical admissions. Yet, each year, it is estimated that 30% of patients undergoing coronary angiography for chest pain have normal coronary angiograms and the prevalence of non-cardiac chest pain (NCCP) in 14 separate populations has been estimated to be 13%. In Australia, NCCP accounts for at least AUS$300 million of the annual health budget.⁵

The prevalence of persistent non-cyclical pelvic pain has been estimated to be about 16% in population studies in both the USA and the UK. Approximately one-third of women with pelvic pain will have no obvious gynaecological pathology and one-third will have persistent pain in spite of hysterectomy. It has been postulated that persistent pelvic pain occurs direct healthcare costs of £158 million, with indirect costs of £24 million each year.

Abdominal pain in childhood is common with 12-month prevalence rates varying from 20% in a population sample to 44% in a general practice cohort. In up to 20% of affected children, episodes are intermittent but recurrent. Only 30% of emergency hospital admissions for abdominal pain result in a definitive diagnosis and in up to 33% of emergency appendectomies the appendix is normal.⁵ Many school days are lost through recurrent hospitalizations or clinic visits, which, in addition to disruption of social activities, may be detrimental to the child’s development and well-being and have significant financial consequences for the family.

It is clear that psychological morbidity is common in patients with visceral pain, whether organic or functional, and an understanding of this issue is crucial to the optimal management of these disorders. What is not clear is how much of this comorbidity is cause and how much is effect. Nevertheless, recognition of this important coexistence must be carefully discussed with patients and other healthcare professionals. Otherwise, patients will be stigmatized as having pain that is psychological in origin, their complaints and distress will not be taken seriously and pharmaceutical companies will not invest in drug development for visceral pain.

Patients with visceral pain need careful assessment and it is entirely correct that they are referred to specialists for investigation and treatment in the first instance. But, often, organic pathology is ruled out and patients are discharged from the acute specialty with the reassurance that no obvious reason for their pain can be found, or they are given treatments in the expectation that the pain will resolve, but it persists. Patients become anxious and concerned that their persistent symptoms indicate that investigations have not been extensive enough, that more tests are needed and that pathology and the reason for their pain has been missed. This situation is made worse if questions are then asked for the first time about previous psychiatric history and present mood and any positive therapeutic relationship can be lost.

Historically, patients with somatic pain formed the largest percentage of patients referred to pain management services. However, I suggest that this will change in the future. The pressure on acute hospital trusts to reduce emergency department attendances, to reduce the number of acute admissions and especially readmissions, will mean that all hospitals need to identify better ways to manage the large number of patients referred with visceral pain. This is where pain management services can assist their trust, by developing unique expertise in these complex problems.

Pain management services should ask themselves if they currently have the knowledge and the training to do this. The International Association for the Study of Pain (IASP) has identified visceral pain as the theme for the Global Year against Pain from October 2012 to October 2013. There are many factsheets on the IASP website that can be downloaded free, as can the organisation’s newsletter, Pain: Clinical Updates. We should ask the following questions. Are we confident in performing vaginal and rectal examinations and, if not, how should we learn? Who should deliver the training? Are we confident that every pain management service can manage visceral pain? Are our services organized to manage in-patient and emergency department referrals? Should visceral pain be managed in tertiary specialist services only? How do we develop the expertise of our own multidisciplinary team? Should we be developing more interdisciplinary clinics with specific specialties?

Chronic or recurrent visceral pain is experienced by a large number of children and adults in the community, in acute hospitals and in out-patient clinics. Visceral pain conditions are associated with a diminished quality of life and exert a huge cost burden through healthcare costs and lost productivity. Patients with chronic or recurrent visceral pain are usually not a high priority for the parent specialty as management can be difficult, yet these patients need to have their pain understood, explained and managed. These patients are deserving of multidisciplinary treatment in pain management services. These services should endeavor to ensure that their staff possess the necessary knowledge, expertise and time to deal with this complex, yet common, problem by developing sound business models with their trust and the clinical commissioning groups.