Polycystic Ovary Syndrome - Pathogenesis

Pathogenesis

Polycystic ovaries develop when the ovaries are stimulated to produce excessive amounts of male hormones (androgens), particularly testosterone, by either one or a combination of the following (almost certainly combined with genetic susceptibility):

• the release of excessive luteinizing hormone (LH) by the anterior pituitary gland
• through high levels of insulin in the blood (hyperinsulinaemia) in women whose ovaries are sensitive to this stimulus

Alternatively or as well, reduced levels of sex-hormone binding globulin can result in increased free androgens.

The syndrome acquired its most widely used name due to the common sign on ultrasound examination of multiple (poly) ovarian cysts. These "cysts" are actually immature follicles, not cysts ("polyfollicular ovary syndrome" would have been a more accurate name). The follicles have developed from primordial follicles, but the development has stopped ("arrested") at an early antral stage due to the disturbed ovarian function. The follicles may be oriented along the ovarian periphery, appearing as a 'string of pearls' on ultrasound examination.

Women with PCOS have higher GnRH, which in turn results in an increase in LH/FSH ratio.

A majority of patients with PCOS have insulin resistance and/or are obese. Their elevated insulin levels contribute to or cause the abnormalities seen in the hypothalamic-pituitary-ovarian axis that lead to PCOS. Hyperinsulinemia increases GnRH pulse frequency, LH over FSH dominance, increased ovarian androgen production, decreased follicular maturation, and decreased SHBG binding; all these steps contribute to the development of PCOS. Insulin resistance is a common finding among patients of normal weight as well as overweight patients.

In many cases PCOS is characterised by a complex positive feedback loop of insulin resistance and hyperandrogenism. In most cases it can not be determined which (if any) of those two should be regarded causative. Experimental treatment with either antiandrogens or insulin sensitizing agents improves both hyperandrogenism and insulin resistance.

Adipose tissue possesses aromatase, an enzyme that converts androstenedione to estrone and testosterone to estradiol. The excess of adipose tissue in obese patients creates the paradox of having both excess androgens (which are responsible for hirsutism and virilization) and estrogens (which inhibits FSH via negative feedback).

PCOS may be associated with chronic inflammation, with several investigators correlating inflammatory mediators with anovulation and other PCOS symptoms.

It has previously been suggested that the excessive androgen production in PCOS could be caused by a decreased serum level of IGFBP-1, in turn increasing the level of free IGF-I which stimulates ovarian androgen production, but recent data concludes this mechanism to be unlikely.

PCOS has also been associated with a specific FMR1 sub-genotype. The research suggests that women who have heterozygous-normal/low FMR1 have polycystic-like symptoms of excessive follicle-activity and hyperactive ovarian function.