Title: Olfactory Dysfunctions in Alzheimer’s Disease
Abstract: Alzheimer’s disease is not only the most frequent cause of dementia that takes its toll on the elder population, but it is also the disorder for which, despite the complex research performed, a certain diagnosis may only be performed through anatomic-pathologic examination. Alzheimer’s disease is a neurodegenerative disease whose defining anatomic-pathologic trait is the deposit of amyloid plaques at the level of certain areas of the brain, the presence of fibrillary degeneration in the neurons and vascular changes with an amyloid deposit, all of which result in the impressive reduction of the cerebral mass noticed in the final stages of the condition. Studies of over 30 years have established that olfaction is impaired in AD, however not invariably. As early as 1987, Rezek described olfactory deficit as a neurological sign in Alzheimer dementia. Recent research has started to clear up potential mechanisms of olfactory loss in Alzheimer’s disease. Alzheimer disease has a selective vulnerability of the cerebral structures to the pathologic process, inducing a distinctive lesion pattern with a slow evolution in time and that is constantly invariable in the study cases. It begins in the transtentorial region and it then expands to the cortical and subcortical components of the limbic system and it may include the association areas of the neocortex. The pathologic process may be progressive, containing 6 stages. In stages 1-2, the pathologic process takes place at the level of the anteromedial temporal lobe mesocortex, the entorhinal allocortex and the horn of Ammon. Such structures are not only related to memory and learning, but also to the olfactory system. Therefore, stage 1-2, considered “clinically silent”, includes a series of non-cognitive clinical changes that are essential for the timely diagnosis of the disease, including olfactory changes. The deficit of the olfactory system in Alzheimer’s disease, as early as its incipient stages, is currently a generally recognized fact. The correlation between olfaction and Alzheimer’s disease is particularly exciting, with important diagnosis practical implications. The olfactory system is a unique system of the human brain; it belongs to archaic structures, its anatomic route is distinguished by the fact that it is the only means of sense that approaches the brain directly, it is the only sensatory system with direct cortical projections, without a thalamic relay, it is the only part of the brain where neurogenesis persists, it has a special reaction to the aging process, it plays an essential role in behavior (food behavior, orientation and sexual behavior) and it influences memory, as there is also a smell memory.