Smelling multiple sclerosis: Different qualities of olfactory function reflect either inflammatory activity or...

Area of Science:

• Neuroscience
• Ophthalmology
• Neurology

Background:

• Peripapillary retinal nerve fiber layer (pRNFL) thickness and olfactory function are emerging biomarkers in multiple sclerosis (MS).
• Olfactory impairment, including odor identification and discrimination, is linked to neurodegeneration in advanced MS.
• Olfactory threshold changes may reflect short-term inflammatory activity in early MS.

Purpose of the Study:

• To validate the association between olfactory function and MS disease course parameters in a large patient cohort.
• To correlate olfactory function with pRNFL thickness as a biomarker for neurodegeneration in MS.

Main Methods:

• Cross-sectional study involving 260 MS patients.
• Olfactory function assessed using the Sniffin' Sticks test (threshold, discrimination, identification).
• pRNFL thickness measured by spectral-domain optical coherence tomography (OCT); data analyzed using multivariable regression.

Main Results:

• Olfactory threshold correlated with recent relapses and shorter disease duration.
• Odor discrimination and identification correlated with longer disease duration, higher EDSS, and reduced cognitive function.
• pRNFL thickness associated with odor identification and discrimination, but not threshold.

Conclusions:

• Olfactory threshold serves as a marker for short-term inflammatory activity in MS, independent of neurodegeneration.
• Odor identification and discrimination indicate neurodegeneration in MS, largely independent of relapse activity.
• Assessing olfactory function can help stratify MS patients based on inflammatory and neurodegenerative profiles.