Motor callosal disconnection in early relapsing-remitting multiple sclerosis

Area of Science:

• Neuroscience
• Radiology
• Neurology

Background:

• Relapsing-remitting multiple sclerosis (RRMS) commonly affects the corpus callosum (CC).
• Macroscopic CC lesions are typical in RRMS, but early microstructural changes may precede them.
• Understanding early CC disconnection is crucial for diagnosing and managing RRMS.

Purpose of the Study:

• To investigate microstructural and effective disconnection of the CC in very early RRMS patients.
• To assess corpus callosum (CC) integrity before macroscopic lesions are evident on conventional MRI.
• To identify potential surrogate markers for early motor callosal disconnection in RRMS.

Main Methods:

• Combined functional MRI and diffusion tensor imaging fiber tracking to identify motor CC fibers (CMFs).
• Assessed CMF microstructural integrity using fractional anisotropy (FA) within the motor CC (FA-CC).
• Measured short-interval interhemispheric inhibition (S-IHI) via transcranial magnetic stimulation (TMS) to evaluate CMF effective connectivity.

Main Results:

• Significantly reduced FA-CC and S-IHI in early RRMS patients compared to healthy controls.
• The correlation between microstructure (FA-CC) and function (S-IHI) present in controls was lost in RRMS patients.
• These abnormalities were observed without macroscopic CC lesions on conventional MRI and with normal motor hand/arm function.

Conclusions:

• Reduced FA-CC and S-IHI indicate early motor callosal disconnection in RRMS.
• These measures may serve as sensitive biomarkers for detecting early-stage RRMS changes.
• Early detection of CC disconnection can inform prognosis and treatment strategies in RRMS.