Quantification of Uhthoff's phenomenon in multiple sclerosis: a magnetic stimulation study

Area of Science:

• Neurology
• Neuroscience
• Clinical Medicine

Background:

• Multiple sclerosis (MS) is a demyelinating disease affecting the central nervous system.
• Uhthoff phenomenon describes the worsening of neurological symptoms with increased body temperature in MS patients.
• The precise mechanisms of temperature-induced motor deficits in MS remain incompletely understood.

Purpose of the Study:

• To quantify temperature-induced changes in central motor conduction in MS patients.
• To investigate the relationship between these changes and clinical motor deficits.
• To explore the role of conduction block versus conduction slowing in Uhthoff phenomenon.

Main Methods:

• Recruited 20 multiple sclerosis (MS) patients.
• Assessed subjective temperature vulnerability and performed clinical examinations.
• Measured central motor conduction time (CMCT) using motor evoked potentials.
• Quantified central motor neuron conduction failure using the triple stimulation technique (TST) and TST amplitude ratio (TST-AR).

Main Results:

• Temperature-induced changes in TST-AR were more pronounced in patients with prolonged CMCT (P=0.037).
• A significant linear correlation was observed between TST-AR changes and walking velocity (P=0.0002).
• Subjective temperature vulnerability correlated with abnormal CMCT, temperature-induced TST-AR changes, and temperature-induced walking velocity changes.

Conclusions:

• Uhthoff phenomenon in the motor system of MS patients is attributed to conduction block, not significant changes in CMCT.
• Patients with central conduction slowing are more susceptible to developing temperature-dependent motor conduction blocks.
• This study provides the first quantification of Uhthoff phenomenon in the MS pyramidal tract.