Olfactory Pathology in Central Nervous System Demyelinating Diseases

Area of Science:

• Neuropathology
• Neuroimmunology
• Demyelinating Diseases

Background:

• Olfactory dysfunction is a frequent symptom in multiple sclerosis (MS).
• Pathology of the olfactory bulb and tract in MS and other demyelinating diseases is not well understood.
• Understanding olfactory bulb and tract involvement is crucial for comprehending MS-related neurological deficits.

Purpose of the Study:

• To investigate olfactory bulb and tract pathology in a spectrum of demyelinating diseases.
• To compare olfactory pathology in demyelinating diseases with neuroinflammatory and neurodegenerative conditions.
• To determine the relationship between demyelination, inflammation, and axonal loss in the olfactory system.

Main Methods:

• Human autopsy cohort including MS, Neuromyelitis Optica (NMO), Acute Disseminated Encephalomyelitis (ADEM), herpes simplex virus encephalitis (HSE), Alzheimer's disease (AD), and non-neurologic controls.
• Histopathological examination of olfactory bulbs and tracts for myelin, axons, and inflammation.
• Analysis of inferior frontal cortex and hippocampus for myelin in a subset of cases.

Main Results:

• Olfactory bulb/tract demyelination was observed in 70.6% of MS, 42.9% of ADEM, and 66.7% of NMO cases.
• Demyelination and inflammation in the olfactory bulb/tract were absent in HSE, AD, and control groups.
• Significant correlation found between olfactory bulb/tract demyelination, axonal loss, and inflammation in MS.
• Olfactory bulb/tract demyelination correlated with inferior frontal cortex pathology but not hippocampal pathology.

Conclusions:

• Olfactory bulb and tract demyelination is a frequent and specific finding in demyelinating diseases.
• This pathology is characterized by inflammation and associated axonal loss, particularly in MS.
• Olfactory bulb/tract demyelination can be an early event and may correlate with central nervous system white matter changes.