ABSTRACT

Olfactory system disorders received much clinical and experimental attention within last two decades as several severe neurological conditions have been associated with peripheral or central deficits of the olfactory system. Some neurodegenerative disorders such as Alzheimer disease (AD) and Parkinson disease (PD) are characterized by early olfactory loss. A number of studies demonstrated the impairments of olfactory memory at early stages of AD [8; 5]. Inability to identify odors in AD patients is secondary relative to inability to detect odors in principle. Olfactory disorders in AD are bilateral and progress as disease is developing [13], [9], [10]. About 95 percent of PD patients show olfactory deficit at preclinical stages of disease. Unlike AD, there is no apparent longitudinal progression in olfactory dysfunction as occurs in other elements of the disease process [3]. In 2006 American Academy of Neurology recommended evaluation of olfactory function for differential diagnostics of PD [15]. Standardized olfactory tests are widely used in clinical practice in the United States for differential diagnostics of neurological disorders. A number of tests based on odor identification are currently applied around a world. Olfactory deficit in AD could be detected by a wide range of olfactory tests, including tests for odor identification, detection threshold sensitivity, discrimination and memory. Nevertheless smell identification tests when respondents requested to select right odor name out of multiple alternates turned out to be the most sensitive. High sensitivity of such tests are explained by pathophysiology of AD development. Development of AD starts from the structures of olfactory system. Entorinal and trans-entorinal brain area, hippocampus and amigdala are the first sites where neurite plates appear (0 stage of AD in accordance with Braque classification). Thus, structures which are critical for olfactory sensitivity and olfactory memory, suffer at the very beginning of AD. Early diagnosis of neurodegenerative diseases such as AD is important for increasing the efficacy of medications that may thwart the progression of the symptoms.