Modeling Uhthoff's phenomenon in MS patients with internuclear ophthalmoparesis

Area of Science:

• Neuroscience
• Ophthalmology
• Neurology

Background:

• Multiple sclerosis (MS) is a demyelinating disease affecting axonal conduction.
• Uhthoff's phenomenon describes the worsening of MS symptoms with increased body temperature.
• Internuclear ophthalmoparesis (INO) is a specific ocular motor deficit observed in MS.

Purpose of the Study:

• To establish internuclear ophthalmoparesis (INO) as a model for studying temperature-induced changes in axonal conduction in MS.
• To investigate the effects of whole-body heating and cooling on ocular motor function in MS patients with INO.

Main Methods:

• Ocular motor function was assessed using infrared oculography in MS patients with INO, MS patients without INO, and healthy controls.
• Measurements were taken at normothermic baseline, during whole-body heating, and after whole-body cooling.
• Key metrics included the versional disconjugacy index (velocity-VDI) and first pass amplitude (FPA).

Main Results:

• MS patients with INO exhibited significantly elevated velocity-VDI and FPA after whole-body heating compared to baseline.
• These ocular motor abnormalities in MS-INO patients were restored to baseline levels after whole-body cooling.
• The findings confirm a reversible compromise in axonal electrical impulse transmission properties due to temperature fluctuations.

Conclusions:

• A neurophysiological model using INO was developed to objectively study temperature-related reversible axonal conduction changes in MS.
• The study corroborates that core body temperature fluctuations (heating and cooling) induce stereotypic decay and restoration of axonal conduction mechanisms.
• This research provides insights into Uhthoff's phenomenon and its impact on neurological function in MS.