Olfactory Dysfunction in Psychiatric and Neurodegenerative Disorders: Clinical Relevance and Potential as a Biomarker

Abstract

Olfactory dysfunction is increasingly recognized as a feature present in both psychiatric and neurodegenerative disorders. It has been linked to alterations in central neural processing as well as to progressive structural changes within the nervous system. This narrative review aims to compare olfactory dysfunction across major depressive disorder, schizophrenia, Alzheimer’s disease, and Parkinson’s disease, with particular emphasis on its clinical relevance and underlying mechanisms. A narrative review of current literature was conducted, focusing on studies assessing olfactory function in the selected disorders. Relevant findings were analysed in terms of clinical presentation, neurobiological correlates, and potential diagnostic value. Olfactory dysfunction was identified across all examined conditions. In psychiatric disorders, deficits appeared to be primarily related to functional alterations and were often dynamic or partially reversible, whereas in neurodegenerative diseases, olfactory impairment was associated with progressive structural and molecular pathology and frequently occurred in the prodromal phase. Across all groups, higher-order olfactory processes, particularly odor identification and discrimination, were most consistently affected. Olfactory dysfunction represents a multidimensional phenomenon that may reflect either transient functional changes or ongoing neurodegeneration, depending on the disorder. Its non-invasive assessment may serve as a useful complementary tool for early detection and monitoring of disease progression.