[Acute low back pain].

A focused history taking and physical examination directed toward uncovering signs that suggest a serious underlying cause of low back pain are crucial. "Red flags" include pain that lasts more than 6 weeks; pain in persons younger than 18 years or older than 50 years; pain that radiates below the knee; a history of major trauma; poor rectal tone; constitutional symptoms; atypical pain (eg, that which occurs at night or that is unrelenting); the presence of a severe or rapidly progressive neurologic deficit; and a history of malignancy. These markers provide a cost-effective means of guiding your selection of laboratory and diagnostic imaging studies. Low back pain affects up to 90% of the population; the annual incidence is 5%. It is second only to upper respiratory tract infection as a symptom-related reason for visits to primary care physicians1-3 and affects men and women equally.2,3 The economic impact of low back pain is enormous. It is the most common cause of work-related disability in persons younger than 45 years and the second most common cause of temporary disability (after upper respiratory tract disease) for all ages. In 1990 the direct and indirect costs (including lost earnings) of diagnosing and treating low back pain totaled more than $58 billion.1-3 Some studies show that in up to 84% of patients with acute low back pain, no clear cause is ever determined.4 Although symptoms usually resolve within 4 to 6 weeks, all patients with back pain should be evaluated fully so that significant neurologic or life-threatening diseases may be ruled out. The "red flags" of back pain are important historical and physical features that point to potentially dangerous conditions. Identification of a red flag warrants close attention and further diagnostic testing. These red flags were defined in a set of guidelines on acute low back pain published by the Agency for Health Care Policy and Research.5 In this article, we discuss the approach to the patient who presents with low back pain-with particular emphasis on red flags. We also review the most common diagnostic procedures. In a future article, we will describe the evaluation and treatment of common and worrisome back pain syndromes as well as the less common, but nonetheless important, presentations of back pain in children and in patients with a history of cancer. THE HISTORY A focused history taking is the most critical tool for identifying risk factors for serious disease in a patient who presents with low back pain. Directing the history taking toward the red flags allows for an efficient, costeffective assessment (Table 1). Duration of symptoms. Low back pain falls into 3 categories based on duration: Acute pain lasts less than 6 weeks. Subacute pain continues for 6 to 12 weeks. Chronic pain persists for more than 12 weeks.6 Pain that lasts longer than 6 weeks raises a red flag because 80% to 90% of all episodes of low back pain resolve within 6 weeks.7 If the patient has been assessed for low back pain previously, and pain persists for more than 6 weeks, he or she requires further evaluation. However, if the patient has had pain for 4 to 6 weeks without appropriate treatment, it is reasonable to delay the workup and observe him closely-provided there are no other red flags. Prescribe analgesia and activity modification measures at the initial visit. If there is no dramatic improvement after 2 weeks, begin the diagnostic workup. In the patient who has chronic symptoms but who has already undergone a complete evaluation, review the workup to ensure that it has been thorough and that vital clues or signs have not been missed. Age. Back pain in patients younger than 18 years or older than 50 years constitutes a red flag.5 In