Pain Disorder

Sidney Benjamin

Stella Morris

Introduction

Persistent somatoform pain disorder is an ICD-10 diagnosis, which is included in the group of somatoform disorders. The term pain disorder is used in DSM-IV, and for convenience that is the term used here to refer to both classifications, unless a distinction needs to be made. This chapter aims to clarify the relationship of pain to mental disorders, the diagnosis of pain disorder and its differential diagnosis, and then considers how psychosocial factors contribute to pain, the treatments that stem from them, and the psychiatrist’s potential contribution.

Pain has been defined by the International Association for the Study of Pain (IASP) as ‘an unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage’. ‘Pain’ is used here in this sense; it is not used primarily to indicate mental distress or anguish. As a perception, pain is essentially a subjective experience, and is directly accessible only to the patient. By contrast, tissue damage can be assessed by others, and its relationship with the subjective characteristics of pain have been shown to be variable, modulated by social and cultural experience, as well as within the central and peripheral nervous system.

Pain and the psychiatrist

Psychiatrists are likely to see patients with pain in psychiatric, general hospital, and community settings. Pain is associated with a wide range of mental disorders, and there are different ways in which this relationship may arise.

Pain may contribute to the cause of a mental disorder; for example, when a patient with cancer has pain, which is unrelieved by analgesics, and becomes depressed. This can result in additional distress and disability, and subsequently an exacerbation of pain. Treatment of depression may contribute to the relief from pain and improve the quality of life.

In a general hospital psychiatrists may see patients with acute pain, like the patient described above, but more often will see patients with chronic pain. Whatever the initial cause, the longer pain persists the more likely is it to result in the development of inappropriate patterns of illness behaviour and to have a profound effect on relationships with the family and other carers, presenting more complex challenges for management and poorer prognosis.

Pain disorder

Diagnostic and clinical features

Persistent somatoform pain disorder in ICD-10 is the only somatoform disorder that is essentially characterized by pain. The diagnostic requirements are as follows:

1 ‘persistent, severe, and distressing pain’;

2 pain ‘cannot be explained fully by a physiological process or a physical disorder’;

3 ‘pain occurs in association with emotional conflict or psychosocial problems that are sufficient to allow the conclusion that they are the main causative influences’.

There are also likely to be many of the features that occur in the other somatoform disorders, which have been described in previous chapters. The pain can be localized, as in low back pain, or generalized, as in fibromyalgia.

In ICD-10, the diagnosis is excluded if pain, presumed to be mainly psychological in origin, occurs in the course of schizophrenia or depressive disorder, or is believed to be due to psychophysiological mechanisms such as muscle tension. The main differential diagnosis, according to ICD-10, is the histrionic elaboration of pain primarily due to organic causes, particularly if this has not yet been diagnosed. In practice, it is uncommon for pain that has been properly investigated, and has persisted for more than 6 months, to be found subsequently to have a specific organic cause.

The DSM-IV diagnosis of ‘pain disorder’ also needs to be considered because the requirements for diagnosis and the underlying rationale are rather different. This diagnosis is divided into three subtypes:

1 ‘Pain disorder associated with psychological factors’, in which psychological factors are judged to play the major role, and physical disorders play either no part or only a minor part in its onset or maintenance.

2 ‘Pain disorder associated with both psychological factors and a general medical condition’, in which both psychological processes and an organic disorder are judged to make important contributions to causation.

3 ‘Pain disorder associated with a general medical condition’, due to an organic disorder and in which psychological factors are judged to make no contribution or to play only a minor role. This subtype is not regarded as a mental disorder but is coded on Axis III.

For the first two subtypes the diagnostic criteria, all of which must be satisfied, are summarized as follows:

Pain, localized or more general, is the predominant symptom and its severity warrants clinical attention
Pain results in distress, and impairment in social, occupational, or other areas of functioning.
Psychological factors are judged to have an important role in the onset, severity, exacerbation, or maintenance of pain.
It is not intentionally produced or feigned (factitious disorder and malingering are specifically excluded).
Pain is not better accounted for by a mood, anxiety, or psychotic disorder and does not meet criteria for dyspareunia.

Pain disorder can also be coded according to whether it is acute or chronic (less or more than 6 months duration).

Comparison of ICD-10 and DSM-IV

The diagnoses of pain disorder in ICD-10 and DSM-IV share a number of characteristics. Pain disorder should be diagnosed as a mental disorder if psychological factors are thought to make a significant contribution to predisposition, precipitation, or maintenance, or to the severity of pain. In ICD-10, there should be evidence that emotional conflict or psychosocial problems are the main ‘causative influences’, whereas in DSM-IV psychological factors are judged to play either the ‘major role’ or ‘an important role’. In both, the diagnosis can be made even though there may be possible or definite evidence of an organic disorder that contributes to pain (for instance, a prolapsed intervertebral disc), provided that this is judged to be insufficient to account fully for the features of pain. Both classifications stress the severity of pain and the distress caused by it, but only DSM-IV specifically requires a degree of disability as a diagnostic feature. The implication is that diagnosis requires detailed physical and psychiatric evaluation, including an assessment of the family and social context, as well as of disability.

Differential diagnosis of pain disorder

Pain can occur in the setting of virtually any mental disorder. Table 5.2.6.1 lists the ICD-10 diagnoses and their DSM-IV equivalents in which pain may be a predominant feature. The general description of most of these disorders is provided in other chapters of this book and the following account focuses only on aspects relevant to pain.

(a) Organic disorders

Many painful disorders have a well-recognized organic pathology that accounts for the occurrence of pain (for example, angina, sickle cell arthropathy), but psychosocial processes tend to modify the severity of pain and associated disability. Thus, psychological and social interventions may make an important contribution to management, and as pain becomes more chronic, or fails to respond to usually effective physical treatments, psychosocial interventions assume greater significance. These disorders can be diagnosed in ICD-10 within the diagnoses headed ‘Psychological interactions with physical disorders’ in Table 5.2.6.1.

(b) Pain syndromes of uncertain origin

There are many disorders characterized by pain, which are essentially syndromes with no known consistent organic pathology (Table 5.2.6.2). Psychological and social factors are thought to contribute to the development and maintenance in many cases,⁽¹⁾ but psychological causes specific to these different syndromes have not been identified. Patients with these pain syndromes tend to have a greater prevalence of non-psychotic mental disorders than is found in the general population. The pain itself can usually be accommodated in ICD-10 within the categories of somatoform autonomic dysfunction or somatoform pain disorder (see below). The ‘diagnoses’ listed in Table 5.2.6.2 tend to be used by non-psychiatrists to describe clusters of medically unexplained symptoms and are terms which are likely to be acceptable to patients. Treatments for these disorders generally include physical approaches, often of limited efficacy, as well as a range of psychosocial interventions, which are described below.

(i) Psychoses

At the beginning of the twentieth century, French psychiatrists described coenestopathic states as disorders characterized by unpleasant sensations, particularly pains, thought to be of central origin, but unrelated to organic brain disease.⁽²⁾ Such disorders were a daily occurrence in psychiatric clinics, commonly associated with the psychoses, and in this setting were related to somatic hallucinations and systematized delusional states. Such presentations are now described infrequently in Europe and North America.

Patients with any psychosis may complain of pain, sometimes with bizarre descriptions of quality and delusional attribution. In practice, it is difficult to differentiate between a somatic hallucination and an illusion (arising from physiological or pathological processes). Complaints of pain in psychotic disorders have no psychiatric diagnostic specificity. Pain has been described particularly in association with schizophrenia and depressive psychoses, but may occur in any psychotic disorder. In the course of a psychotic disorder, illusions and delusional interpretations of pain may arise from unrelated organic disorders and therefore require careful physical assessment.

(ii) Mood- and anxiety-related disorders

These are by far the most common mental disorders associated with pain in most settings. In the general population, 12 per cent of adults have experienced chronic widespread pain (defined according to the criteria of the American College of Rheumatologists) in the previous 3 months and their prevalence of mental disorders is three times that of the pain-free population.⁽³⁾ Most of these diagnoses are mood and anxiety disorders, with the former being more common in those with chronic pain. In pain clinic settings, the prevalence of mental disorders varies according to referral patterns, but about 30 to 40 per cent of patients have depressive disorders, and this is similar in those with and those without a relevant physical disorder.⁽⁴⁾ Those without organic disorders tend to have lower ratings for both mood disorders and pain severity. Those with mood disorders report more severe pain.

Diagnosis of mood and anxiety disorders is based on the usual standardized criteria, but may be missed due to the process of somatization, particularly where patients attribute their depressed mood to pain and an underlying physical condition (whether present or not) and invite their doctors to share this belief.⁽⁵⁾ In the past, pain has been thought of as a proxy for depression, giving rise to the concept of a ‘depressive equivalent’ or ‘masked depression’. This has been based mainly on evidence for the psychogenicity of chronic pain rather than a specific relationship to depressive disorders, has received widespread criticism, and has not advanced theoretical knowledge or clinical practice.

(iii) Post-traumatic stress disorder

Many patients with post-traumatic stress disorder (PTSD) have been subjected to actual or threatened physical injury, so it is not surprising that pain is one of the commonest symptoms that they report, the prevalence ranging from 20 to 80 per cent. Further, 10 to 50 per cent of patients with chronic pain satisfy criteria for PTSD, and patients with musculoskeletal pain are four times more likely to develop PTSD than those without it.⁽⁶⁾ Pain disorder and PTSD can be diagnosed jointly, if criteria for both are satisfied. Mechanisms including shared vulnerability, fear-avoidance, and mutual maintenance have been postulated to account for this comorbidity.⁽⁷⁾ This has implications for assessment (described below), and treatment programmes may need to be modified accordingly.

Table 5.2.6.1 Mental disorders included in the differential diagnosis of pain disorder

ICD-10		DSM-IV
Psychotic disorders
F00-09	Organic mental disorders	290	Dementia 293 Delirium
F20-29	Schizophrenia, schizotypal, and delusional disorders	273	Schizophrenia and other psychotic disorders
Mood- and anxiety-related disorders
F32/33	Depressive episode	296.2/3	Major depressive disorder
F34.1	Dysthymia	300.4	Dysthymic disorder
F41	Anxiety disorders	300.02	Generalized anxiety disorder
F43.1	Post-traumatic stress disorder	309.81	Post-traumatic stress disorder
F43.2	Adjustment disorders	309	Adjustment disorders
Somatoform disorders
F44.4	Dissociative (conversion) disorders	300.11	Conversion disorder
F45.0	Somatization disorder	300.81	Somatization disorder
F45.1	Undifferentiated somatoform disorder	300.81	Undifferentiated somatoform disorder
F45.2	Hypochondriacal disorder	300.7	Hypochondriasis
F45.3	Somatoform autonomic dysfunction	300.8	Pain disorder
F45.4	Somatoform pain disorder	300.81	Somatoform disorder NOS
F45.8	Other somatoform disorders
F45.9	Somatoform disorder, unspecified
Other neurotic disorders
F48.0	Neurasthenia
F48.8	Other specified neurotic disorders (occupational neurosis, e.g. writer’s cramp)
Sexual disorders
F52.5	Non-organic vaginismus	306.51	Vaginismus
F52.6	Non-organic dyspareunia	302.76	Dyspareunia
Psychological interactions with physical disorders
F54	Pyschological or behavioural factors associated with disorders or diseases classified elsewhere	316	Psychological factors affecting medical condition
F68.0	Elaboration of physical symptoms for psychological reasons
Disorders of behaviour
F68.1	Intentional production or feigning of symptoms	300.19	Factitious disorder
		V65.2	Malingering
Comorbidity of pain disorder
Any of the above except psychoses and other somatoform disorders
Substance abuse
F10	Disorders due to alcohol	291 & 303.9	Alcohol-induced disorders and dependence
F11-13	Disorders due to psychoactive substance abuse	292 & 304	Other substance-induced disorders and dependence
F55	Abuse of non-dependence-producing substances		Other substance-induced disorders and dependence
Personality disorders
F60-62	Personality disorders and changes	301	Personality disorders