Increased Cortical Excitability in Female Migraineurs: A Transcranial Magnetic Stimulation Study Conducted in the Preovulatory Phase

BACKGROUND AND PURPOSE: The cerebral cortex has been the focus of investigations of the pathogenesis of migraine for a long time. Transcranial magnetic stimulation (TMS) is a safe and effective technique for evaluating cortex excitability. Previous studies of the duration of the cortical silent period (CSP)—a measure of intracortical inhibition—in migraine patients have yielded conflicting results. We aimed to characterize cortical excitability by applying TMS to female migraineurs during the preovulatory phase of the menstrual cycle, in order to eliminate the effects of variations in sex hormones. METHODS: We enrolled 70 female subjects: 20 migraine with aura (MA) patients, 20 migraine without aura (MO) patients, and 30 healthy controls. We measured the CSP, resting motor threshold (rMT), and motor evoked potential (MEP) induced by TMS to evaluate cortical excitability during the preovulatory phase of the menstrual cycle. RESULTS: The CSP was shorter in MA patients (88.93±3.82 ms, mean±SEM) and MO patients (86.98±2.72 ms) than in the control group (109.06±2.85 ms) (both p=0.001), and did not differ significantly between the MA and MO groups (p=0.925). The rMT did not differ significantly among the groups (p=0.088). MEP(max) was higher in MA patients than in healthy controls (p=0.014), while that in MO patients did not differ from those in MA patients and healthy controls (p=0.079 and p=0.068). CONCLUSIONS: We detected a shorter CSP in both MA and MO patients. This finding may indicate the presence of motor cortex hyperexcitability, which is probably due to reduced GABAergic neuronal inhibition in migraine.