Does abnormal interhemispheric inhibition play a role in mirror dystonia?

Area of Science:

• Neuroscience
• Movement Disorders
• Clinical Neurology

Background:

• Mirror dystonia, characterized by involuntary movements in one hand when the other isTasked, suggests abnormal brain hemisphere interaction.
• Writer's cramp is a focal dystonia affecting hand movements during writing.
• Understanding interhemispheric communication is crucial for elucidating the pathophysiology of focal dystonias.

Purpose of the Study:

• To investigate interhemispheric inhibition (IHI) levels in writer's cramp patients with and without mirror dystonia.
• To compare IHI in affected and unaffected hands across patient groups and controls.
• To correlate IHI levels with disease severity and duration in writer's cramp.

Main Methods:

• Dual-site transcranial magnetic stimulation (TMS) was used to measure bidirectional interhemispheric inhibition (IHI).
• IHI was assessed at short (10 ms) and long (40 ms) interstimulus intervals.
• Measurements were taken in wrist muscles during rest and pen-holding in patients with mirror dystonia, without mirror dystonia, and controls.

Main Results:

• Patients with mirror dystonia exhibited significantly decreased IHI compared to controls and patients without mirror dystonia.
• This reduction in IHI was observed in both the affected (dystonic) and unaffected hands.
• Lower IHI levels correlated negatively with disease severity and duration, indicating a weaker inhibition in more advanced cases.

Conclusions:

• Disturbances in interhemispheric inhibition are strongly implicated in the development of mirror dystonia.
• The findings suggest that deficient inhibition between brain hemispheres contributes to the pathophysiology of unilateral dystonia.
• The unaffected hemisphere plays a role in the manifestation of dystonia, even when symptoms are unilateral.