[Olfactory Nerve: The Vulnerability Inherent in its Unique System and Neurological Diseases].

Area of Science:

• Neuroscience
• Ophthalmology
• Infectious Disease

Background:

• The olfactory nerve has unique features like direct CNS projection and regeneration.
• Olfactory dysfunction is increasingly recognized in neurological and infectious diseases.
• Understanding olfactory pathways is crucial for diagnosing and managing related pathologies.

Purpose of the Study:

• To review the foundational mechanisms of olfaction.
• To examine the pathophysiology of olfactory dysfunction in COVID-19 and Parkinson's disease (PD).
• To propose a broader understanding of PD-related hyposmia.

Main Methods:

• Literature review of olfactory nerve anatomy, coding, and regeneration.
• Analysis of scientific evidence on olfactory dysfunction in COVID-19.
• Examination of studies on alpha-synuclein aggregation and olfactory loss in PD.

Main Results:

• COVID-19 associated olfactory dysfunction involves SARS-CoV-2 targeting sustentacular cells, leading to gene downregulation and parosmia.
• Alpha-synuclein aggregation in PD nasal mucosa shows incomplete correlation with olfactory dysfunction.
• PD-related hyposmia may be linked to systemic factors like metabolic deficits and neural network issues, not just peripheral aggregation.

Conclusions:

• Olfactory dysfunction mechanisms differ between COVID-19 and PD.
• PD-related hyposmia suggests a systemic vulnerability rather than solely peripheral pathology.
• A multifaceted approach is needed to understand olfactory pathologies in PD and COVID-19.