Excitability of the motor cortex in patients with migraine changes with the time elapsed from the last attack

Francesca Cortese,Francesco Pierelli,Mariano Serrao,Cherubino Di Lorenzo,Vincenzo Parisi,Davide Di Lenola,Gianluca Coppola

doi:10.1186/s10194-016-0712-z

Abstract

BackgroundMotor-evoked potentials (MEPs) produced by single-pulse transcranial magnetic stimulation (TMS) of the motor cortex can be an objective measure of cortical excitability. Previously, MEP thresholds were found to be normal, increased, or even reduced in patients with migraine. In the present study, we determined whether the level of cortical excitability changes with the time interval from the last migraine attack, thereby accounting for the inconsistencies in previous reports.MethodsTwenty-six patients with untreated migraine without aura (MO) underwent a MEP study between attacks. Their data were then compared to the MEP data collected from a group of 24 healthy volunteers (HVs). During the experiment, the TMS figure-of-eight coil was positioned over the left motor area. After identifying the resting motor threshold (RMT), we delivered 10 single TMS pulses (rate: 0.1 Hz, intensity: 120% of the RMT) and averaged the resulting MEP amplitudes.ResultsThe mean RMTs and MEP amplitudes were not significantly different between the MO and HV groups. In patients with MO, the RMTs were negatively correlated with the number of days elapsed since the last migraine attack (rho = -0.404, p = 0.04).ConclusionOur results suggest that the threshold for evoking MEPs is influenced by the proximity of an attack; specifically, the threshold is lower when a long time interval has passed after an attack, and is higher (within the range of normative values) when measured close to an attack. These dynamic RMT variations resemble those we reported previously for visual and somatosensory evoked potentials and may represent time-dependent plastic changes in brain excitability in relation to the migraine cycle.

Highlights

Motor-evoked potentials (MEPs) produced by single-pulse transcranial magnetic stimulation (TMS) of the motor cortex can be an objective measure of cortical excitability
We recently found that in migraineurs, the degree of EP abnormalities fluctuates over time, in relation to the occurrence of migraine attacks [4,5,6]
No differences in interictal resting motor threshold (RMT) or MEP amplitudes were noted between the two participant groups (t = 0.536, p = 0.594 and U = 305.0, p = 0.892, respectively; Fig. 3)

Summary

Introduction

Motor-evoked potentials (MEPs) produced by single-pulse transcranial magnetic stimulation (TMS) of the motor cortex can be an objective measure of cortical excitability. The pathophysiology of migraine remains unclear, neurophysiological studies performed over the last few decades have shown that patients affected by migraine exhibit interictal abnormalities in their cortical information processing system [1, 2] These functional brain abnormalities are not constant; rather, they cyclically change until an attack occurs, whereupon the Cortical excitability can be examined noninvasively by applying transcranial magnetic stimulation. Thresholds for MEPs were found to be normal [8,9,10,11,12,13], increased [14,15,16], or reduced [17,18,19] in migraineurs Whether these inconsistent findings result from variation in the cortical excitability related to the time interval between the ictal and interictal state remains unknown

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Results

Discussion

Conclusion