Neuronal hyperexcitability is thought to play a pivotal role in the pathogenesis of hemiplegic migraine (HM). Cortical excitability of the motor cortex can be evaluated using transcranial magnetic stimulation (TMS). However, previous interictal TMS studies have yielded contradictory results in HM patients.

This retrospective cohort study characterized intracortical inhibitory and facilitatory networks in HM patients using TMS applied to the motor cortex. Single- and paired-pulse TMS paradigms were used to assess motor evoked potentials (MEP), cortical silent period (CSP), short-interval intracortical inhibition (SICI), long-interval intracortical inhibition (LICI), and intracortical facilitation (ICF). Data were collected from 12 HM patients (8 female; mean age 32.3 ± 11.3 years), including four with an ATP1A2 pathogenic variant, three with a SCN1A pathogenic variant, and five without an identified variant. Results were compared to normative reference data from 26 age- and sex-matched healthy participants assessed using the same TMS protocol.

Between migraine attacks, HM patients exhibited a shorter CSP duration (median 72.8 ms [IQR 49.9–122.1] vs. 107.8 ms [IQR 98.2–128.4]; P = 0.049) and decreased SICI (median ratio 111.8% [IQR 69.1–188.5] vs. 31.0% [IQR 18.2–54.4]; P < 0.001) and LICI (median ratio 75.5% [IQR 26.8–98.9] vs. 15.0% [IQR 1.2–26.9]; P = 0.012), indicating impaired inhibitory mechanisms. In contrast, ICF was not significantly different between groups ( P = 0.23). Two patients examined during an ongoing attack showed complete absence of MEPs from the affected hemisphere.

These preliminary findings suggest that impaired cortical inhibition, reflected by reduced SICI and LICI, may contribute to the pathophysiology of HM. Conversely, intracortical facilitation (ICF) was not significantly altered with the present protocol. Replication in larger cohorts is needed.