Where does it hurt? Describing the body locations of chronic pain

Chronic pain patients have complex problems. Due to this, much research effort has been expended on the classification of pain patients and the classification of pain problems. A mainstay of most pain classification systems is the use of the physical location of the pain. Yet describing the location of the patient's pain is not straightforward. Many patients have pain at multiple sites and thus simple statements such as 'patients with low back pain' have considerable ambiguity. Does the statement refer to patients with pain just in the lower back or those with low back pain who may also have pain elsewhere (e.g. pain down the leg)? If patients do have pain elsewhere, at what other body sites and what are the implications of this? This paper presents data on the body location of pain for a large sample of 5279 patients seen with chronic pain in Scotland and the north of England. It shows that one-third of patients have pain in multiple locations, and that using a single body site to classify patients leads to groups with large overlaps. Thus, 38% of patients reported pain in the 'lower back/spine' and 34% reported pain in the 'buttock, leg, foot' - but there was considerable overlap between these groups. Nineteen percent of patients reported pain in both of these body areas, and one-third of these patients also had pain in at least one further body area. Furthermore, a systematic look at patients with diverse physical pain locations but a single site in common shows large demographic differences. Common pain groupings help to reduce the confusion; 13 pain site descriptions were able to account for 82% of all patients. The remaining 18% of patients had pain in a combination of body sites which they shared with fewer than 1% of other patients. Thus, pain patients are widely heterogeneous and complex. Patients report pain in more complex patterns than can easily be captured by a single body-site code. Further, large demographic differences between patients with different painful sites, even when they have at least one pain site in common, suggests that grouping patients based on a single site descriptor may be inappropriate. These findings have important implications for chronic pain description and classification.