Epidemiological definition of chronic widespread pain

Musculoskeletal conditions usually present with pain and loss of function. The patient complains of chronic musculoskeletal pain, which could be due to a number of different illnesses. The real frequency of the original musculoskeletal conditions, as a result, is difficult to assess because it is marred by case-definition uncertainties and differences in the methods adopted in the epidemiological studies . Pain, an important symptom of joint diseases, is also an index of severity and activity of the underlying condition, as well as a prognostic/therapeutic indicator and a determinant of health-resources use. The three clinical features of the condition that constitute the topic of this article are pain, chronicity and widespread localisation. The definition of pain, according to sources such as the International Association for the Study of Pain (IASP) and World Health Organization (WHO), has been already addressed in this issue of Best Practice Clinical Rheumatology . IASP defined pain as “an unpleasant sensory and emotional experience associated with actual or potential damage or described in terms of such damage” . According to the American College of Rheumatology (ACR) 1990 criteria, chronic widespread pain (CWP) is defined as pain that is bilateral, above and below the waist, in the axial skeleton and lasts for at least 3 months . This definition was used for developing the diagnostic criteria of fibromyalgia. Hunt et al. proposed a slightly different definition of CWP, describing it as pain that has been present for at least 3 months in at least two sections of two controlateral limbs and in the axial skeleton . This definition can identify also people with CWP related to fatigue, distress and psychological problems. Generally, pain caused by malignant, metabolic or infectious disorders is not included in CWP. In summary, pain should last at least 3 months to be considered chronic and should be localised simultaneously both in the axial and peripheral skeleton, affecting both parts of the body. These definitions, however, cannot discriminate between pain directly localised in the joints or bones and pain originating from the surrounding tissues, such as ligaments, tendons and tendon sheaths, fasciae, muscles and bursae. For the sake of epidemiological studies, this differentiation is unnecessary because musculoskeletal pain at large is investigated.