The olfactory disorder may be one of the first manifestations of neurodegenerative brain disease. It has been described and studied in detail in Parkinson's disease and other neurodegenerative diseases.
Recently, it has come to the forefront of interest as one of the early markers of Alzheimer's disease, which can also be used in differential diagnosis. The authors present a clear article dealing with the specific olfactory disorders in individual diseases, olfactory tests and the application of olfactory examination in the diagnosis of neurodegenerative diseases.