Transcallosal inhibition in amyotrophic lateral sclerosis

Area of Science:

• Neuroscience
• Neurology
• Biomedical Engineering

Background:

• Upper motor neuron (UMN) assessment is crucial for amyotrophic lateral sclerosis (ALS) diagnosis.
• Mirror movements (MM) in ALS can indicate transcallosal pathway involvement alongside UMN dysfunction.

Purpose of the Study:

• To investigate if deficient transcallosal inhibition (TI), assessed via transcranial magnetic stimulation (TMS), can identify cortical changes in ALS patients, particularly in early disease stages.
• To determine the utility of TI measurement in detecting subclinical cortical involvement in ALS.

Main Methods:

• TMS was employed to measure contralateral (cMEP) and ipsilateral (iMEP) motor evoked potentials.
• Transcallosal inhibition (TI) latency and duration were analyzed in 3 definite and 12 early ALS patients.
• Recordings were taken from both first dorsal interosseus muscles.

Main Results:

• 83.3% of ALS patients exhibited pathological TI (prolonged or absent inhibition).
• Five patients with pathological TI showed no clinical UMN signs; two of these had MM.
• TI testing revealed abnormalities even in the absence of overt clinical UMN signs.

Conclusions:

• Functional deficits in transcallosal pathways are present in early ALS stages, preceding clinical UMN signs.
• Measuring TI using TMS can detect cortical output system involvement in ALS.
• TI assessment via TMS may assist in the early diagnosis of ALS.