Abstracts

Even though about one third of female epileptic patients show anovulatory cycles, apparent seizure clustering in those cycles is not well understood. The aim of this study was to further investigate changes in cortical excitability during anovulatory as compared to ovulatory cycles using transcranial magnetic stimulation (TMS). Using single- and paired- pulse TMS, 12 healthy women were investigated during ovulatory cycles (progesterone levels in luteal phase [gt] 5 ng/ml, age: 25.5 [plusmn] 4.9 years, BMI: 21.0 [plusmn] 1.3 kg/m[sup2], cycle length: 26.9 [plusmn] 1.9 days) and 8 during anovulatory cycles (progesterone levels [lt] 5 ng/ml, age: 24.1 [plusmn] 2.2 years, BMI: 22.5 [plusmn] 2.5 kg/m[sup2], cycle length: 29.0 [plusmn] 1.1 days). On days 8, 14, 21 and 2 of the cycle, resting motor threshold (RMT), cortical silent period (CSP), intracortical inhibition (ICI, averaged values of interstimulus intervals (ISI) 2 and 3 ms) and facilitation (ICF, averaged values of ISIs 10 and 15 ms) were investigated in the dominant hemisphere. Friedman and Wilcoxon tests were used for intraindividual comparisons over time within each group. Two-sample Mann-Whitney U tests were used to detect differences between groups at each point of measurement: ICI varied during anovulatory cycles (p = .040), mainly due to an increased inhibition at day 2 (median (range): day 8: 50 % (32[ndash]98 %); day 14: 39 % (20[ndash]74 %); day 21: 49 % (33[ndash]59 %); day 2: 29 % (17[ndash]64 %)). There were no differences in ICI during ovulatory cycles (p = .564, median (range): day 8: 64 % (30[ndash]97 %); day 14: 80 % (35[ndash]129 %); day 21: 63 % (33[ndash]90 %); day 2: 57 % (30[ndash]100 %)). Comparing ICI in ovulatory and anovulatory subjects inhibition was less pronounced in ovulatory cycles at day 14 (p = .025), day 21 (p = .043) and day 2 (p = .007). RMT, CSP and ICF showed no significant changes during ovulatory or anovulatory cycles. The results suggest that fluctuations of cortical excitability exist also during anovulatory cycles. As estrogen withdrawal initiates bleeding in anovulatory cycles, the increased inhibition at this time may be caused by lowered proconvulsive estrogen levels. Decreased inhibition in ovulatory as compared to anovulatory cycles may reflect the estrogen peak preceding ovulation on day 14 and possibly higher estrogen levels during the luteal phase.