New Neuropathological Criteria for Alzheimer's Disease

Currently, Alzheimer's disease is usually diagnosed in two ways. The first is by clinical examination of patients, including tests of cognitive abilities such as memory, problem solving, attention, and language. The second is by neuropathological examination after death, in which brain tissue is examined under the microscope for characteristic signs of disease such as plaques and tangles. In April 2011, the clinical diagnostic criteria for Alzheimer's disease were revised for the first time in 27 years by a series of expert panels convened by National Institute on Aging and the Alzheimer's Association. The new clinical criteria incorporate a deeper understanding of Alzheimer's disease, recognizing that the symptoms of the disease develop gradually over many years. The new clinical guidelines describe the earliest preclinical stages of the disease, as well MCI and dementia due to Alzheimer's pathology.

In late 2011, the neuropathology guidelines for Alzheimer's disease-in use since 1''7-were similarly updated to reflect advances in diagnosing the disorder in brain tissue. The new guidelines incorporate a new understanding of the relationship between the clinical and neuropathological signs of the disease. In contrast to the old guidelines, the new ones no longer require that individuals receive a diagnosis of dementia while living in order for their brains to be examined for signs of Alzheimer's disease after death. This change reflects the realization in recent years that the brains of many cognitively normal older individuals contain significant amounts of amyloid plaque, which may represent the early stages of Alzheimer's disease.

In the new guidelines, inspection of brain tissue for the presence of plaques and tangles remains central to diagnosis. However, the guidelines now ask pathologists to report in more detail the amounts and locations of plaques and tangles within the brain, and to check for them even in the brains of people who appeared free of dementia while living.

The new guidelines also require that brains be examined for signs of other diseases that may contribute to cognitive decline, such as cerebrovascular disease or Lewy body disease, and which often coexist with Alzheimer's in the brains of older people. Finally, the new guidelines recommend that in research settings, genetic risk markers and new biomarkers be used in conjunction with neuropathological and clinical data to follow the progression of the disease and to study its underlying mechanisms (Hyman et al., 2012).