Data were collected from a consecutive series of 1242 new patients referred to the Comprehensive Pain Program (CPP) of the Toronto Western Hospital (a University of Toronto affiliated teaching hospital) at the University Health Network (Toronto, Ontario) over the course of three years (2001 to 2004), after approval by the University Health Network Research Ethics Board. All demographic data were provided by the patients through standardized intake questionnaires completed at the time of their original consultation (age, sex, place of residence, country of birth, language spoken at home, years of education, marital status, employment at onset of pain and at time of first consultation at the pain clinic, as well as body maps for patients to mark their pain areas). Clinical information was obtained at the time of the examination by experienced pain physicians, through a comprehensive history based on a standardized format and detailed neuromusculoskeletal (neuro-MSK) examination. Additionally, information was retrieved from a review of pertinent documentation (previous investigations and operative reports, if any), as well as follow-up visits and further investigations when needed. Each patient was seen initially and at follow-up by the same pain physician. All three of the physicians who participated in the present study were trained in the same pain clinic (with a collective experience of 40 years and approximately 15,000 new patients by the end of the study in 2004). Detailed recording of neuropathic pain disorders, MSK problems, and visceral and complex syndromes was obtained based on a specified list of multiple disorders created for the data collection. Examples of complex syndromes include failed back surgery syndrome and thoracic outlet syndrome – these entities are a mix of several pain types and mechanisms. If a patient had more than one medical problem, the medical problems were listed separately. Psychiatric comorbidity and determination of psychosocial factors were important parts of the clinical interview because the clinicians noted and recorded, in detail, the behaviours and psychosocial factors that may have had an impact on pain perception and/or expression. Selected patients seemed to have complex diagnoses and could not be assessed well on an outpatient basis. These patients were admitted to the inpatient unit for further investigations and lengthy behavioural observations, in addition to psychological and psychiatric assessments, in the context of a multidisciplinary team assessment.
The CPP physicians categorized diagnoses of pain disorders in accordance with the American Psychiatric Association’s 1994 and 2000 versions of the DSM, the DSM-IV (7
) and the DSM-IV-TR (10
), respectively. This facilitated treatment decision-making, based on recognition of both medical and nonmedical factors that contribute to a patient’s pain and disability. DSM-IV pain disorder diagnoses were routinely recorded in patient files over the previous 14 years. The authors’ understanding developed over time with experience regarding observations obtained during encounters with patients, together with other information considered to be pertinent indicators of psychological factors contributing to presentation. For the purpose of presenting the data obtained in the current study and other similar studies (8
), the specific criteria listed below were suggested retrospectively by the pain physicians. These suggestions represent what they thought were the most salient and important criteria for arriving at a pain disorder diagnosis. The clinicians suggested that a minimum of one class A and two class B factors (see below) could be relied on to make these diagnoses. Subsequently, the proposed criteria were evaluated in a retrospective chart analysis of 30 randomly selected consultation records. Indeed, information in the charts confirmed that use of the criteria did result in the pain disorder diagnosis that had been made for the patient. In summary, two specific classes of factors relating to physical pathology (A) and psychological variables (B) have been proposed, as follows:
- Factors related to underlying physical (organic) pathology:
- Symptom congruence with known medical condition and/or anatomy and physiology, including pain severity and level of disability;
- File review documenting relevant pathology (consultations, test results, operative reports, electrophysiological and other studies, etc); and
- Abnormal specific findings on examination relevant to a given condition.
- Factors related to psychological or behavioural variables that augment and perpetuate the pain, and are considered to be associated with the onset, maintenance, exacerbation or severity of pain:
- Multiple verbal and nonverbal pain behaviours (grimacing, verbalization, gestures, posturing, etc) markedly in excess of expectation given the associated pathology;
- Significant fear of pain or pain avoidance behaviours (for example, immobilization of an arm or complete avoidance of weight-bearing in the absence of pathology warranting such a treatment);
- Incongruent affect to pain ratings (eg, 10/10 pain ratings in a smiling and laughing patient);
- Restricted and persistently high pain ratings (eg, pain always 8/10, 9/10 or 10/10 and never lower);
- Level of disability markedly in excess of expectation based on underlying pathology (eg, bed-bound for weeks or months after minor soft tissue injury, as in Whiplash Associated Disorder I or II; inability to perform any but the lightest of household chores or need for assistance with activities of daily living in the presence of minor, if any, pathology, etc);
- Bizarre or nonphysiological signs incongruent with any known pathology or disease (eg, unexplainable movement disorder involving tremor, choreiform or athetoid movements, dyskinesiae, etc, bearing characteristics of psychogenic movement disorders; severe weakness or paralysis; pain generated by physiologically unrelated or simulated manoeuvres, eg, mere bending of the knee producing back pain, palpation of the shoulder generating leg pain, light compression of the head generating lower extremity or back pain, etc);
- Inconsistent performance during interview and/or physical examination over time and situation (marked discrepancies between distraction and confrontation testing in multiple situations, such as straight leg raising, range of movement, disappearance of posturing, tremor or movement disorder under distraction or suggestion, as well as behaviour or demeanour that changes when the patient is unaware that he or she is being observed, etc);
- Diffuse body pain elicited by light digital palpation including the trunk and/or limbs, significantly modifiable by attention or distraction, and in the absence of specific underlying joint disorder or other disorder;
- Behaviours and pain ratings altered by the presence of a solicitous spouse or significant other, as observed by the examiner or reported explicitly to the examiners by family members;
- Pain reported by the patient to be markedly increased by psychosocial stressors or significantly relieved by situations considered by the patient to be relaxing or not stressful;
- Unusual patterns of pain occurrence (eg, cyclical patterns of pain appearing “always at a set time on specific days of the week” or “half an hour after getting out of bed”, pain appearing suddenly after a particular exercise and remaining chronic in the absence of demonstrable pathology, pain always being the worst at night when going to bed when the patient attempts to relax and “has nothing to do” in the absence of pathology known to be associated with nocturnal pain, etc);
- Recurrent short-term benefits or, to the contrary, recurrent pain exacerbations after multiple unrelated interventions (eg, dramatic response to a multiplicity of different medications lasting only a few days or weeks; major, multiple or bizarre side effects from all drugs used, even at miniscule doses; persistent pain generated after simple physical examination or physiotherapeutic intervention, etc);
- Onset of pain problem occurring in the context of an emotionally charged situation which may be followed by persistent manifestations of emotional distress, eg, post-traumatic stress disorder;
- Presence of a significant mood or anxiety disorder (other than post-traumatic stress disorder) thought to impact on pain perception and/or behaviour, conspicuously present or elicited during the interview, or documented by the treating psychiatrist or psychologist (including interventions such as antidepressants or antianxiety drugs specifically administered for a mood or anxiety disorder, electrotherapy, psychological treatments for anxiety or panic disorders, etc);
- Known history of multiple other pain problems suggestive of psychological factors contributing to presentation or other known somatoform disorders (pseudoseizures, psychogenic movement disorders, somatization disorder, etc); or
- Other (specify).
Based on the above system, the presence of one or more class A factors qualifies the patient for a chronic pain disorder diagnosis associated only with biomedical pathology (not a psychiatric diagnosis) and indicates the presence of significant and congruent physical pathology accounting for the patient’s symptoms (group I). In most cases, more than one class A factor was recognized. The presence of two or more class B factors alone rendered the diagnosis of a chronic pain disorder associated with psychological factors (group III). In group III, psychological factors are judged to have a major role in the onset, severity, exacerbation or maintenance of the pain. The presence of factors from both class A and B resulted in the diagnosis of a chronic pain disorder associated with both psychological factors and a general medical condition (group II).
Statistical analyses using F and χ2 statistics, as appropriate, were conducted to assess whether there were statistically significant differences among pain disorder classifications, comparing patients 65 years of age and older with patients younger than 65 years of age, and comparing adults 65 to 74 years of age and adults 75 years of age and older. Because of the small population size of adults 85 years of age and older (n=8), there were no separate analyses for this subgroup. Statistical analyses were also conducted to determine whether there were age-or sex-related differences in the diagnosis of neuropathic versus MSK disorders. In addition to the P value for any statistically significant finding, a measure of effect size has been reported. References have been made to the larger sample of 1242 patients, from which this particular study group was derived, when appropriate.