出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2012/04/21 18:27:34」(JST)
| Amenorrhea | |
|---|---|
| Classification and external resources | |
| ICD-10 | N91.0-N91.2 |
| ICD-9 | 626.0 |
| DiseasesDB | 14843 |
| eMedicine | article/953850 |
| MeSH | D000568 |
Amenorrhoea (BE), amenorrhea (AmE), or amenorrhœa, is the absence of a menstrual period in a woman of reproductive age. Physiological states of amenorrhoea are seen during pregnancy and lactation (breastfeeding), the latter also forming the basis of a form of contraception known as the lactational amenorrhoea method. Outside of the reproductive years there is absence of menses during childhood and after menopause.
Amenorrhoea is a symptom with many potential causes. Primary amenorrhoea (menstruation cycles never starting) may be caused by developmental problems such as the congenital absence of the uterus, failure of the ovary to receive or maintain egg cells, and genetic diseases such as 5-alpha-reductase deficiency which causes one to be intersex. Also, delay in pubertal development will lead to primary amenorrhoea. It is defined as an absence of secondary sexual characteristics by age 14 with no menarche or normal secondary sexual characteristics but no menarche by 16 years of age. Secondary amenorrhoea (menstruation cycles ceasing) is often caused by hormonal disturbances from the hypothalamus and the pituitary gland, from premature menopause or intrauterine scar formation. It is defined as the absence of menses for three months in a woman with previously normal menstruation or nine months for women with a history of oligomenorrhoea.[1]
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There are two primary ways to classify amenorrhoea. Types of amenorrhoea are classified as primary or secondary, or based on functional "compartments" (Speroff).[2] The latter classification relates to the hormonal state of the patient that could be hypo-, eu-, or hypergonadotropic (meaning FSH levels are either low, normal or high).
| P/S | Outflow tract anomalies/obstruction | Gonadal/end-organ disorders | Pituitary and hypothalamic/central regulatory disorders |
|---|---|---|---|
| Overview | The hypothalamic-pituitary-ovarian axis is functional. | The ovary or gonad does not respond to pituitary stimulation. Gonadal dysgenesis or premature menopause are possible causes. Chromosome testing is usually indicated in younger individuals with hypergonadotropic amenorrhoea. Low oestrogen levels are seen in these patients and the hypo-oestrogenism may require treatment. | Generally, inadequate levels of FSH lead to inadequately stimulated ovaries which then fail to produce enough oestrogen to stimulate the endometrium (uterine lining), hence amenorrhoea. In general, women with hypogonadotropic amenorrhoea are potentially fertile. |
| FSH | Outflow tract abnormalities tend to be normogonadotropic and FSH levels are in the normal range. | Gonadal, usually ovarian, abnormalities tend to be linked to elevated FSH levels or hypergonadotropic amenorrhoea. FSH levels are typically in the menopausal range. | Both hypothalamic and pituitary disorders are linked to low FSH levels leading to hypogonadotropic amenorrhoea. |
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Women who go through significant weight loss, dieting, or perform considerable amounts of exercise on a regular basis are at risk of developing hypothalamic (or 'athletic') amenorrhoea. It was thought for many years that low body fat levels and exercise related chemicals (such as beta endorphins and catecholamines) disrupt the interplay of the sex hormones estrogen and progesterone. However, recent studies have shown that there are no differences in the body composition, or hormonal levels in amenorrhoeic athletes as compared to regularly cycling athletes. Instead, amenorrhoea has been shown to be directly attributable to a low energy availability. Many women who diet or who exercise at a high level do not take in enough calories to expend on their exercise as well as to maintain their normal menstrual cycles.[6]
A second serious risk factor of amenorrhoea is severe bone loss sometimes resulting in osteoporosis and osteopenia. It is the third component of an increasingly common disease known as female athlete triad syndrome. The other two components of this syndrome are osteoporosis and disordered eating. Awareness and intervention can usually prevent this occurrence in most female athletes. Many doctors simply prescribe the combined oral contraceptive pill to women with hypothalamic amenorrhoea, and these women continue in their patterns of under-eating and over-exercising. Often, they do not realize that they have a problem until they are trying to conceive, when their amenorrhoea leads them to seek the treatment of a reproductive endocrinologist.[7]
Certain medications, particularly contraceptive medications, can induce amenorrhoea in a healthy woman. The lack of menstruation usually begins shortly after beginning the medication and can take up to a year to resume after stopping a medication. Hormonal contraceptives that contain only progestogen like the oral contraceptive Micronor, and especially higher-dose formulations like the injectable Depo Provera commonly induce this side-effect. Extended cycle use of combined hormonal contraceptives also allow suppression of menstruation. The use of opiates (such as heroin) on a regular basis has also been known to cause amenorrhoea in longer term users.
Treatments vary based on the underlying condition. Key issues are problems of surgical correction if appropriate and oestrogen therapy if oestrogen levels are low.
For those who do not plan to have biological children, treatment may be unnecessary if the underlying cause of the amenorrhoea is not threatening to their health.
Unless receiving eggs from an egg donor or in vitro fertilization, a woman is unable to conceive while she is amenorrhoeic. On the other hand, 'athletic' and drug-induced amenorrhoea has no effect on long term fertility as long as menstruation can recommence. The best way to treat 'athletic' amenorrhoea is to decrease the amount and intensity of exercise. Similarly, to treat drug-induced amenorrhoea, stopping the medication on the advice of a doctor is a usual course of action.
The term is derived from Greek: a = negative, men = month, rhoia = flow. Derived adjectives are amenorrhoeal and amenorrhoeic. The opposite is the normal menstrual period (eumenorrhoea).
In preindustrial societies, menarche typically occurred later than in current industrial societies. After menarche, menstruation was suppressed during much of a woman's reproductive life by either pregnancy or nursing. Reductions in age of menarche and lower fertility rates mean that modern women menstruate far more often than they did under the conditions prevalent for most of human evolutionary history.[8]
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| リンク元 | 「機能性視床下部性無月経」 |
| 関連記事 | 「function」「functional」「hypothalamic」「hypothalami」 |