The second question, is does any additional diagnostic accuracy provided by the CSF test matter? In clinical practice, a laboratory test that confirmed Alzheimer's disease would remove ambiguity in early cases and limit consideration of other disorders that may present with symptoms suggestive of Alzheimer's dementia such as Creutzfeldt-Jakob disease, frontotemporal dementia, normal pressure hydrocephalus, Parkinson's disease with Lewy body dementia, vascular dementia, and depression. In some of these diseases, prompt diagnosis could lead to earlier effective treatment, such as shunting for normal pressure hydrocephalus or antidepressive medications for depression.
The truly persuasive argument for CSF testing in clinical practice would be the reality of a disease-modifying therapy that prevents or slows the progression of Alzheimer's disease. However, not only is there no "magic bullet" for the prevention of Alzheimer's disease, there is no bullet at all. The current treatments offer modest, temporary, and symptomatic improvement at best. For most patients with mild cognitive deficits concerned about the development of Alzheimer's disease, a careful history, physical, and neurological evaluation with close clinical follow-up (a "wait and see" approach) is practical and appears cost effective.
Once people become demented, they can no longer plan for their financial future or dictate their end-of-life care. An early diagnosis of Alzheimer's disease, rather than late, permits a person more autonomy in directing his or her future. However, an early diagnosis of Alzheimer's disease may have negative psychological consequences in an otherwise well-functioning person who must now consider an inexorable decline towards a state of personal oblivion. Consequently, the pros and cons of early diagnosis must be carefully weighed in each individual prior to such a confirmatory test.
The success of clinical trials requires not only that the treatment be effective, but that all subjects have the disease in question. Subjects who have other diseases contaminate the sample and confound results. To improve the likelihood of successful clinical trials for Alzheimer's disease, potential subjects should be considered for CSF and other diagnostic testing. Revision of research criteria for the diagnosis of Alzheimer's disease that includes abnormal biomarkers has been proposed.
Current Indications for CSF Testing
At present, CSF and other biomarker Alzheimer's testing should be reserved for patients who present a diagnostic dilemma, patients with suspected dementia for whom a diagnosis of probable Alzheimer's disease would provide more solace than worry, and patients entering clinical trials.