Screening for Dementia in Primary Care: A Summary of the Evidence for the U.S. Preventive Services Task Force

Dementia is an acquired syndrome of decline in memory and at least one other cognitive domain, such as language, visuospatial, or executive function, that is sufficient to interfere with social or occupational function in an alert person (1). Many diseases can cause the dementia syndrome (hereafter called dementia). Alzheimer disease and cerebrovascular ischemia (vascular dementia) are the two most common causes, and some cases of dementia involve both of these disorders. Although some potentially reversible conditions, such as hypothyroidism or vitamin B12 deficiency, are often thought to cause dementia, no more than 1.5% of cases of mild to moderate dementia are fully reversible (2). Age is the best-studied and strongest risk factor for dementia. Other risk factors for Alzheimer disease include having a first-degree relative with a history of Alzheimer disease and having the apolipoprotein E 4 genotype (3-5). Cardiovascular risk factors such as hypertension are associated with an increased risk for both Alzheimer disease and vascular dementia (5-7). The aging of the U.S. population has been accompanied by a dramatic increase in the prevalence of dementia. Three percent to 11% of persons older than 65 years of age and 25% to 47% of those older than 85 years of age have dementia (8-13). In 1997, the number of persons with Alzheimer disease in the United States was estimated to be 2.3 million, more than 90% of whom were 60 years of age and older (14). Dementia causes a high burden of suffering for patients, their families, and society (15-21). For patients, it leads to increased dependency and complicates other comorbid conditions. For families, it leads to anxiety, depression, and increased time spent caring for a loved one. The annual societal cost of dementia is approximately $100 billion (health care and related costs as well as lost wages for patients and family caregivers) (10, 16, 22). Clinicians using routine history and physical examination do not readily diagnose dementia during clinic visits. More than 50% of persons with dementia, including many with mild but some with moderate dementia, have never received a diagnosis of dementia from a physician (23-27). This raises the possibility that screening tests might be able to identify persons with undiagnosed dementia and thereby permit patients and their families to receive care at an earlier stage in the disease process. Given the low prevalence of reversible causes of dementia, a recommendation for screening would depend on evidence of the additional benefits of earlier treatment for persons whose dementia has an irreversible cause, primarily Alzheimer disease and vascular dementia. For dementia screening to lead to improved health outcomes, primary care providers would need a brief, accurate screening test that could be applied during routine office visits. A positive result could then lead to a diagnostic interview and clinical examination based on the Diagnostic and Statistical Manual of Mental Disorders, fourth edition (DSM-IV), that could be performed by the primary care physician or a specialist, such as a geriatrician or neurologist. Finally, knowledge of dementia at an early stage could improve health outcomes through more effective treatment. Ideal evidence to support these hypotheses would come from a randomized, controlled trial (RCT) of screening and earlier intervention, with long-term follow-up for both adverse and beneficial effects of screening. The 1996 Guide to Clinical Preventive Services from the U.S. Preventive Services Task Force (USPSTF) found insufficient evidence to recommend for or against screening for dementia (28). Since the last USPSTF review, studies have been published concerning screening tests as well as both pharmacologic and caregiver interventions. Given the new evidence and the growing importance of this condition, the RTIUniversity of North Carolina Evidence-based Practice Center conducted a systematic review of the literature on the benefits and harms of screening primary care populations to detect undiagnosed dementia. Our review did not consider screening to detect persons with cognitive impairment, termed mild cognitive impairment, who do not meet the criteria for dementia. Experts do not agree about the definition of mild cognitive impairment, and other reviews have not found evidence of effective treatment for persons with this problem (29, 30). Methods Using USPSTF methods (31), we developed an analytic framework and eight key questions to guide our systematic review of the evidence for dementia screening. We developed eligibility criteria for selecting evidence that could answer the key questions and then used them, in turn, to develop search terms. We searched MEDLINE, PsycINFO, EMBASE, and the Cochrane Library databases for systematic reviews and high-quality studies relevant to each question. We limited all searches to reviews and studies that were published in English between 1 January 1994 and 1 September 2002 and contained information relevant to a primary care population. We searched first for studies providing direct evidence that screening improves cognitive, social, or physical function; number of hospitalizations, institutionalizations, or health care visits; behavioral problems; caregiver burden; accidental injuries, such as falls or automobile crashes; or patients' overall health-related quality of life. Because we found no direct evidence connecting screening and improved health outcomes, we searched for indirect evidence of screening benefit, including the prevalence of undiagnosed dementia; the accuracy of screening tests; the efficacy of early pharmacologic and nonpharmacologic treatment for persons with Alzheimer disease and vascular dementia; caregiver intervention for persons with dementia; and the efficacy of interventions targeted to caregivers. We also searched for evidence of the adverse effects of screening and treatment. At least two authors reviewed abstracts and articles to identify those that met the eligibility criteria and then abstracted relevant information using standardized abstraction forms. We graded the quality of the included articles using USPSTF criteria (31). In all cases, we accepted single studies or systematic reviews that addressed the key questions, met eligibility criteria, and were rated to be at least fair quality. Table 1 lists these criteria and the number of articles that met them for each question. A more thorough account of the methods used in this review can be found in the Appendix. Table 1. Key Questions, Eligibility Criteria, and Number of Articles Meeting Criteria This evidence report was developed by the RTIUniversity of North Carolina Evidence-based Practice Center under contract to the Agency for Healthcare Research and Quality. Staff of the funding agency and members of the USPSTF contributed to the study design, reviewed draft and final manuscripts, and made editing suggestions. Results The best evidence for or against screening for dementia would be derived from a well-designed RCT of screening with health outcomes. No such trial has been completed. In the absence of such a trial, evidence for or against screening comes from studies of the prevalence of undiagnosed dementia, the accuracy of screening instruments, the efficacy of treatments for persons with dementia detected by screening, and the harms of screening and treatment. How Common Is Undiagnosed Dementia? Three studies in primary care samples of patients 65 years of age and older compared dementia detected by using standard diagnostic tests with documentation of dementia or cognitive impairment in the medical record (26, 27, 32) or with dementia noted on independent physician questionnaires (27). Among all primary care patients 65 years of age and older, 3.2% to 12% met criteria for dementia without dementia documentation or physician knowledge of dementia (Table 2). A population-based study found that the prevalence of undiagnosed dementia among persons 65 years of age and older was 1.8% (33). Another population-based study found that approximately half of reliable relatives of men with mild dementia failed to recognize that the men had problems with thinking or memory (81). Table 2. Estimates of Undiagnosed Dementia in Primary Care Practices Patients who had not received a dementia diagnosis accounted for 50% to 66% of all cases of dementia in the primary care samples studied. Most missed cases were mild to moderate. In one small study, 78.6% of persons with mild dementia (11 of 14), 71.4% of persons with moderate dementia (5 of 7), and 20% of persons with severe dementia (1 of 5) had no documentation of a dementia diagnosis in the medical record (27). New screening in primary care practice could therefore potentially double the number of patients who receive a diagnosis of dementia. Most newly detected cases would be mild to moderate. How Accurate Are the Screening Tests? Three methodologic problems make it difficult to assess the accuracy of screening tests for dementia. First, the accuracy of many screening instruments has been researched, but to a limited degree. Few instruments have been examined in more than two or three small studies. Second, investigators have used a variety of reference standards for the diagnosis of dementia. Because functions such as cognition are continuous, the reference standard must set the point at which dementia can be diagnosed. Where this point is set makes a large difference in evaluating screening tests (82). Although research has yet to determine the optimal point for diagnosing dementia, the DSM-IV criteria are widely accepted in the United States and will be used as the standard in this review (83). Third, the samples used in the studies of screening instruments varied greatly. Many studies included participants with severe dementia or persons from memory clinics, who are not the focus of screening. Few studies have provided information o