Epidemiological Hurdles for the Determination of the Prevalence of Chronic Pain with Neuropathic Features

How does one attempt to outline the prevalence of a condition such as chronic pain within a large population? There are numerous potential solutions to this proposition, but also abundant hurdles with each approach. In addition, the nature of chronic pain is one of a collection of diverse conditions not easily recognized or diagnosed . There are several methods that can be used to attempt to answer this question. In past decades, this would often consist of retrospective reviews within one patient population suffering from a single condition . Although useful for condition-specific information, this approach suffers from a lack of reliability and an inability to extrapolate findings to a larger general population. Despite scanty information until the last decade, there have been many advances in determining the epidemiology of chronic pain. Many forward strides have been accomplished through more standardized definitions for chronic pain , followed by the development of standardized questionnaires that can be delivered in person, through mail delivery, or via telephone. New technology has provided novel mechanisms for contacting large portions of a general population, such as with the telephone and the Internet. In particular, the development of valuable, time-efficient questionnaires has assisted greatly in expanding epidemiological studies with a postal , computer Internet , or telephonic basis. Comparing the predictive accuracy of these different questionnaires is difficult, although there is clear overlap in pain descriptor items within each. While we anticipate future scientific advances, at the present, questionnaires such as these provide the most sensitive and specific method of diagnosis in a mass population. However, these cannot be considered a step above the formal, structured clinical assessment of the pain specialist, which is still the “gold standard.” Although these have represented a step forward in determining the demographics of chronic pain, limitations still abound. The return rate with postal studies is notoriously low , and the responders may represent persons with the condition who have a vested interest in discussing their problem as opposed to persons without the condition. It is inherently difficult to determine who is performing an Internet survey and to ensure that the population being investigated is descriptive of the general population. In addition, Internet surveys will tend to involve technological-savvy subjects. Telephonic surveys have their own limitations; even though response rates tend to be higher—many persons no longer have landline telephones or will not answer the telephone, particular if the callee is male. These drawbacks to telephonic surveys are balanced by cost-effectiveness, wide distribution of permissible subjects, and the ability to pose standardized questions. All of these methodologies, however, suffer from a significant limitation in that the persons being surveyed cannot be seen directly by the investigators to identify their composite of symptoms and to perform physical examinations, permitting a standard diagnosis to be provided. This limits our ability to define the true etiology of the chronic pain. These are difficult stumbling blocks for our understanding of the epidemiology of chronic pain. In this edition of Pain Medicine, the Moroccan study of Harifi et al. helps to answer this question further by assessing a different general population from those interrogated previously. Previous studies examining prevalence of chronic pain with neuropathic characteristics have been carried out in the United Kingdom , France , Austria , and Canada . Morocco, located in North Africa, is a country far less developed than countries previously investigated. Although subject to much European influence, higher rates of illiteracy, unemployment, and poverty abound. As such, an investigation of chronic pain prevalence in Morocco will permit stimulating contrasts and comparisons to be made with the former studies. Harifi et al. performed a nationwide telephonic survey using a random sampling of households and a stratified sampling technique. This group used a modified Arabic Douleur Neuropathique 4 (DN4) questionnaire developed by Bouhassira et al. and also identified the single, most painful body part along with other key demographics. Their study was large in scope with over 5,000 responders participating. They reported a prevalence of chronic daily pain for more than 3 months in 21% of the Moroccan population surveyed. As anticipated in other populations, the prevalence of chronic pain rose with age and with female gender. For those subjects with neuropathic characteristics as part of their chronic pain (determined by having a DN4 questionnaire score of ≥3), there was greater pain intensity and longer duration. The prevalence values obtained are more in keeping with European studies than the Canadian study. This difference may relate to the question being posed, as hypothesized by the authors. Harifi et al. asked subjects “Do you currently suffer from pain every day?” while Toth et al. provided the question “Do you have pain on a daily or near daily basis?” . Another potential difference that may have led to differences in the prevalence of neuropathic characteristics as compared with the study of Toth et al. is the characterization of body location experiencing the most severe pain, which was not requested in Toth et al.'s Canadian study . However, it is of great interest that even in an Arabic-speaking Islamic country with definite cultural, sociological, and religious differences, the epidemiology of chronic pain with neuropathic features is not so unlike that of more westernized countries. Although chronic pain is potentially influenced by culture and religion , the prevalence and demographics of this condition seem to transcend these concepts, telling us a great deal about the condition itself. For example, although the prevalence of musculoskeletal pain varies from country to country (as high as 45% in the United States to as low as 11% in Sweden) , do the features and comorbidities contributing to the overall condition really differ that much? The results of Harifi et al. suggest that potential differences across countries and cultures may be less striking than the similarities. New challenges may thwart future studies. Our society has moved away from landline telephones to cellular telephones (which could not be evaluated by Harifi et al.), and new telemarketing regulations will prevent wide-scale and representative future telephonic studies. Thus, as our populations shift to older ages, it will likely be more difficult to perform such similar studies in the future. This is ironic, as our population is more connected electronically and with social media than ever before, but these changes may permit new methodologies to develop, such as with polls using Twitter . Fortunately, it is possible that health differences between persons with listed telephone numbers are not that dissimilar from those with unlisted telephone numbers —it is yet to be determined if such similarities will exist between those with landline telephones and cellular telephones. New innovations will need to be considered to permit health care personnel to keep updated with changing demographics for conditions such as chronic pain having neuropathic characteristics. The author has neither conflicts of interest nor disclosures to describe regarding this editorial.

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