Chronic pain affects more than 100 million people in the United States  and accounts for 20 percent of outpatient visits, 12 percent of all prescriptions, and over 100 billion dollars in direct and indirect expenses . Pain-related expenditures (direct costs and lost wages) in the United States exceed those for cancer, heart disease, and diabetes combined . The use and misuse of opioids for management of chronic pain is a major concern, with problems arising from their multiple adverse side effects including drug dependency, from drug diversion, and from undertreatment of chronic pain symptoms for fear of narcotic abuse. Chronic pain is thus a major medical and social issue, affecting the quality of life of individual patients, their friends and families, the work force, and society in general.
A comprehensive pain evaluation is essential to develop an effective plan for treatment. Although there are unique aspects to every individual's pain complaints, there are many common elements to the pain evaluation, irrespective of the pain complaint. An appropriate history and physical examination are vital to proper evaluation. Laboratory studies, imaging, and other diagnostic testing may be appropriate in selected situations.
The evaluation of patients complaining of persistent pain is discussed here. The definition, classification, and pathogenesis of chronic pain, and overview of its treatment are discussed separately. (See "Overview of the treatment of chronic pain" and "Definition and pathogenesis of chronic pain".)
COMMON CAUSES OF CHRONIC PAIN
Although pain is one of the most common presenting symptoms to the primary care clinician, only a percentage of patients ultimately develop a chronic pain syndrome. In a study based on a survey of representative population in the United States from 1999 to 2002 (the National Health and Nutrition Examination Survey, NHANES), chronic pain (defined as >three months of pain) was reported as follows: back pain 10.1 percent, leg/foot pain 7.1 percent, arm/hand pain 4.1 percent, headache 3.5 percent, chronic regional pain 11.1 percent, widespread pain 3.6 percent; the majority of patients who reported chronic pain reported more than one type of pain .
Chronic pain can be considered to be in one of four categories. Identifying which of these categories the patient falls into is helpful in designing an appropriate treatment plan, although multifactorial causes of chronic pain are not uncommon. These pain categories can be considered to be :