Multimodal evoked potentials and the ovarian cycle in young ovulating women

Potenciais evocados nas diferentes fases do ciclo menstrual da mulher

MULTIMODAL EVOKED POTENTIALS AND THE OVARIAN CYCLE IN YOUNG OVULATING WOMEN

LUIZ ANTONIO DE LIMA RESENDE^*, MARIA DORVALINA SILVA^**, FABÍOLA IMPEMBA^**, NÍDIA BORGES ACHÔA^**, ARTHUR OSCAR SCHELP^* .

ABSTRACT - There is controversy over how hormonal conditions influence cerebral physiology. We studied pattern-shift visual evoked potentials (PS-VEP), brain stem auditory evoked potentials (BAEP) and short-latency somatosensory evoked potentials (SSEV) in 20 female volunteers at different phases of the menstrual cycle (estrogen phase, ovulatory day and progesterone phase). Statistical analysis showed decreased latencies for P₁₀₀ (PS-VEP), N₁₉ and P₂₂ (SSEV) waves in the progesterone phase compared with the estrogen phase. There was no significant difference between the estrogen and the ovulation day values. Comparing the three above stages, there were no significant differences in the brainstem auditory evoked potentials. The reduction of the latencies of the potentials generated in multisynaptic circuits provides the first consistent neurophysiological basis for a tentative comprehension of human pre-menstrual syndrome.

KEY WORDS: evoked potentials, multimodal, ovarian cycle.

Potenciais evocados nas diferentes fases do ciclo menstrual da mulher

RESUMO - Há controvérsias sobre como variações hormonais do ciclo menstrual da mulher influenciam a neurofisiologia cerebral. Estudamos potenciais evocados de curta latência, visuais, auditivos e sômato-sensoriais, em 20 mulheres voluntárias normais, nas diferentes fases do ciclo menstrual (fase estrogênica, fase ovulatória, fase progestacional). Comparação entre fase estrogênica e ovulatória mostrou resultados similares. Ondas I, III, V dos potenciais evocados auditivos não apresentaram diferenças estatisticamente significativas entre as três fases do ciclo. Análise estatística dos resultados mostrou diminuição significativa das latências das ondas P100, N19 e P22 obtidas na fase progestacional, comparadas com aquelas obtidas na fase estrogênica. Como estas ondas são geradas em circuitos multissinápticos, tal redução de latências, na fase progestacional, fornece a primeira base neurofisiológica consistente para tentativa de compreensão da síndrome pré-menstrual da mulher.

PALAVRAS-CHAVE: potenciais evocados, multimodais, ciclo menstrual.

The menstrual cycle influences different clinical conditions such as atopic dermatitis¹, diabetes, asthma, rheumatoid arthritis², pulmonary edema, cardiac arrithmias and gastrointestinal dysfunctions³. Catamenial hemoptisis, catamenial hemothorax and catamenial hemopneumothorax are all well documented clinical conditions⁴. In neurology, illnesses such as myastenia gravis, multiple sclerosis, arteriovenous aneurysms, meningioma, epilepsy, and migraine may be worse during the catamenial or pre-menstrual phases^{3, 5-7}. EEG also varies during different phases of the menstrual cycle⁸.

There is controversy over how hormonal conditions influence cerebral physiology. Some authors⁹, analyzing brainstem auditory evoked potentials (BAEP), found a significant increase in wave III and V latencies, as well as the I-V intervals, associated with elevated levels of estrogen in the luteal phase. No significant differences in latencies were found in ovulatory cycles comparing groups using and not using oral contraceptives. Other authors, however, comparing patients with or without pre-menstrual syndrome (late luteal phase dysphoric disorder) did not find variations in latencies of BAEP related to any phase of the menstrual cycle¹⁰. Differences were also observed in the latencies of pattern-shift visual evoked potentials (PS-VEP), with increased latencies in pregnant compared to non-pregnant women¹¹. There is disagreement in medical literature about how hormonal variations from different phases of the menstrual cycle influence evoked potentials in women.

This study analyzes the PS-VEP, BAEP, and SSEP in a group of young ovulating women during three different hormonal stages of the menstrual cycle.

METHOD

Twenty young, normal white female medical volunteers (ages 23 to 26) participated in this study. They were made fully aware of the nature of the procedures and gave their formal consent. Only women with a clear knowledge of their ovulation were included. Patients not aware of their ovulation time (indicated by changes in vaginal secretion, cramps, and mood changes) and those using hormonal contraceptives or experiencing irregular cycles were excluded. In 5 volunteers the exact moment of ovulation was in the late evening or overnight, and the evoked potentials could not be obtained.

PS-VEP, BAEP and SSEP measurements were taken from the 2^nd to the 7^th day of the cycle (estrogenic phase - EP), on the day of ovulation (ovulatory phase - OP), and from the 6^th to the 1^st pre-menstrual day of the cycle (progesterone phase - PP).

Multimodal measurements were taken at random by the same examiner using a 2-channel Nihon-Kohden Neuropack II apparatus.

PS-VEP were generated with a 1 grade contrast -reversed pattern at 2 Hz stimulus. Analysis time was 300 ms, band-pass filter 5 to 20 Hz and sensitivity 5 mV/cm. A minimum of 2 series of 100 stimuli were averaged for each individual test. The records were analyzed for the left and right peak latencies of P₁₀₀.

BAEPs were obtained in response to 15 Hz rarefaction clicks of 85 dB lasting 0.2 ms. Analysis time was 10 ms, band-pass filter 200 to 3,000 Hz and sensitivity 0,31 mV/cm. A minimum of 2 series of 1000 stimuli were averaged for each individual test. The records were analyzed for the left latencies of waves I, III and V.

SSEPs were obtained in response to a 5 Hz square wave pulse of continuous electrical stimulus lasting 0,2 ms applied by 7 mm surface disc electrodes, 2 cm apart, on the right median nerve at the wrist. In each case the stimulus intensity was just above that necessary for minimal thumb movements. The analysis time was 50ms, band-pass filter 20 to 3,000 Hz and sensitivity 1.25 mV/cm. A minimum of 2 series of 500 stimuli were averaged for each individual test.

Electrode positioning, nomenclature of the waves, and methodology was according to Chiappa¹².

Statistical analysis was performed using the paired t-test.

RESULTS

Statistical analysis showed a decrease of latencies recorded for the P₁₀₀ (PS-VEP), and N₁₉ and P₂₂ (SSEP) when the progesterone phase was compared with the estrogen phase. There was no significant difference between the estrogen and ovulatory phase SSEP when comparing the progesterone phase to the estrogen phase (Table 1).

No differences were recorded for BAEP when the three above refered phases of the menstrual cycle were compared (Table 1).

Examples of slight decreases in P₁₀₀ latencies obtained in the progesterone phase in relation to the estrogen phase are shown in Figure 1.

Examples of slight decreases in N₁₉ and P₂₂ latencies obtained in progesteronic phase in relation to the estrogen phase are shown in Figure 2.

One patient became pregnant after her study cycle. One year later, during the last three months of the pregnancy, the potentials obtained were similar to the progesterone phase prior to the pregnancy (Figure 3).

DISCUSSION

Latency reductions in the visual P₁₀₀ and somatosensory N₁₉ and P₂₂ evoked potentials in the third, progesterone, phase of the cycle are complex. It has been demonstrated that even in women using combined anovulatory therapy, significant follicular activity with luteinization occurs, with or without ovulation¹³. Thus, even with the determination of the luteinizing hormone (LH) and ultrasonography, it is not possible to determine precisely what is the hormonal moment of the menstrual cycle. In this study there was no distinction made between a precocious and late luteal phase, which makes it difficult to affirm that latency changes are related to the progesterone phase. Experimental studies have not demonstrated that conjugate estrogens, applied topically or intravenously, affect the latencies of visually evoked potentials¹⁴.

It is important to point out that the the P₁₀₀, N₁₉, and P₂₂ potentials are generated in multisynaptic pathways, and that the observed reduced latencies during the progesterone phase are probably caused by progesterone action on neuronal circuits. On the other hand, it could be hypothesized that the anatomical pathways in the I, III, V, of the BAEP and N₉, P/N ₁₃ of the SSEP are less susceptible to hormonal fluctuation. The reduction of the progesterone phase latencies generated in multisynaptic circuits provides a neurophysiological basis for understanding the human pre-menstrual syndrome. Further studies are required to confirm the above findings.

Dr. Luiz A. L. Resende - Department of Neurology and Psychiatry, Faculty of Medicine of Botucatu - UNESP - 18618-000 Botucatu SP - Brasil. Fax [phone].

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*

Department of Neurology and Psychiatry, Faculty of Medicine of Botucatu of the State University of São Paulo (UNESP):

Assistent-Professor;

**

Medical Resident. Aceite: 9-março-2000.

Publication Dates

• Publication in this collection
  06 Dec 2000
• Date of issue
  June 2000

History

• Accepted
  09 Mar 2000