This Canadian study provides detailed information on the demographic and pain characteristics of 644 consecutive new patients attending PWC, an academic community-based pain clinic in the GTA. Our population consisted primarily of well-educated middle-age patients, often presenting with severe pain (in accordance with previous literature) [3] due to a car accident, disease or with spontaneous onset, with an average of seven or more years of pain duration. Forty-one percent had a primarily biomedical cause for their pain (group I), 43% had mixed biomedical and psychological/psychosocial pathology (group II), and 16% had evident psychopathology with no substantial detectable medical pathology (group III). Chronic widespread pain (CWP) was found in 11% of the entire cohort (15% of females and 5% of males), and was twice as prevalent in patients younger than 65 years of age. Low back pain was present in 66% of the population, but was the sole site of pain in less than one third of patients with low back pain. Our data on single- vs non-single-site LBP is consistent with the published literature [19]. While opioids were used by one in three patients, the majority of users (83%) were below 90 mg of morphine equivalent with a mean daily consumption of 30 mg morphine equivalent. Interestingly, our present data confirm the preponderance of Canadian-born patients between high-opioid users, similar to the observations we made several years earlier in a downtown Toronto population in an academic centre [10]. Notably, the presence of CWP (considered the result of central sensitization) [20] or non-anatomical sensory abnormalities (attributed to involvement of central nervous system maladaptive neuroplastic changes) [21] is associated with a poor prognosis for response to all therapeutic modalities (drugs, interventions, multimodal treatments, etc.) and return to gainful employment.

In an effort to understand patient characteristics and their relevance to treatment interventions, we attempted to compare our data to those obtained in a university-affiliated pain clinic in a Toronto tertiary-care hospital setting [8, 9], as well as a community-based clinic population (CHANGEpain) in British Columbia [12] and the Quebec registry data collected from five tertiary-care pain centres [11]. As data collection and batteries differed widely, only a few variables could be compared across the four different data sets. More comparable data were available from our previous study in a Toronto tertiary-care setting (Comprehensive Pain Program, or CPP) [8, 9]. Data from the four cohorts are shown in Table 4.

Interestingly, there was little variability across the four populations with respect to age, duration of pain, sex ratio or marital status. When it came to more comparable data between the PWC and CPP populations, similarities were demonstrated in regard to female preponderance, percentage of foreign-born, marital status and high opioid use, which was more prevalent in patients born in Canada than foreign-born patients. On the other hand, we found several differences between the PWC and CPP groups: the PWC cohort had a higher prevalence of older patients (> 65), patients with higher education, more likely to hold employment (full-time, part-time, self employed), and more likely to have biomedical pathology as the sole cause of pain. Opioid consumption differed as well between the groups in the sense that fewer PWC patients consumed opioids and in lower doses. The latter was attributable to a significant change in the climate of opioid use over the last decade (the CPP data were collected 13–16 years earlier), but did not change the fact that high opioid use is seen more frequently in Canadian-born patients. Some of these differences can be attributed to differences in populations, as the PWC is located in a large urban city north of Toronto serving primarily this city and several urban and rural areas above, while the CPP represented a mix of inner-core Toronto patients as well as patients throughout the province of Ontario.

We must stress that there are limitations in comparing populations across these four different data sets. The cohorts were all subject to substantial differences in settings, data collection, time of data collection, batteries used, analysis and regional variables. Several other factors relating to CNCP populations attending the above-described pain clinics could not be assessed, as patient referrals are often influenced by the expertise of a particular clinic, the needs of a given geographic area, distance from the clinic, physician training and specialization, preferences of both referring physicians and patients, availability and access to clinical services, length of waiting list and reimbursement considerations [22].

On the other hand, despite these limitations, we were able to deduce from the available data certain common characteristics between pain clinic populations, as well as substantial differences. We believe that understanding the population attending a particular clinic is of paramount importance for appropriate pain management. For example, older patients are more reluctant to take medications [23], something we have confirmed in the Toronto pain population we studied several years ago [9], and that we empirically confirm in our interactions with our present PWC population. Reluctance to take appropriate medications may pose a barrier to treatment for older patients with serious biomedical pain conditions, particularly when many other options are not feasible. The high proportion of PWC patients that cite car accident, slip-and-fall accident, or work-related injuries (39% of our population) as the cause of pain includes involvement of the medicolegal system and compensation issues, and is relevant in our practice as it potentially reduces response to treatment. The literature indeed shows that such patients have inadequate response to traditional modalities when compared to pain patients not afflicted with compensatory injuries and may suggest benefits to alternative interventions [24].

The notion of patient phenotyping for chronic pain has already been adopted in the context of pain and clinical trials [25]. For example, clear sex and ethnic group differences have been demonstrated in response to multidisciplinary pain management programs [26, 27]. In our own hands, phenotyping of our population provides us with treatment guidance. We have reported high rates of success in group II patients admitted to an intense customized interdisciplinary pain management program, both at the time of “graduation” from our program, and 6 and 12 months after program exit, with improvement ranging between 29 and 77% in different measures [28]. On the other hand, individuals who experience extensive biomedical pathology (group 1) have been successfully managed with medical interventions (manual therapy, medications, injections, surgery).