Spironolactone and intermenstrual bleeding in polycystic ovary syndrome with normal BMI

Spironolactone (SP) is an effective treatment for polycystic ovary syndrome (PCOS), but it is often associated with menstrual abnormalities whose mechanism is still under investigation. In this study, we investigated the serum sex steroids and endometrial thickness in 30 PCOS patients, before and after one-month 100 mg SP treatment.

Serum FSH, LH, estradiol, progesterone and endometrial thickness were evaluated at the 14th and 16th day of the menstrual cycle, before and during short-term SP treatment. According to the presence (15 cases) or absence (15 cases) of menstrual bleeding at the 14th day during SP, the patients were divided into two groups, which were then compared using a two-tailed Student's t test.

Serum estradiol and endometrial thickness were lower than pretreatment at both determinations in all patients, but patients with bleeding had significantly lower estradiol values than non-bleeding ones, both before and after therapy. Endometrial thickness was significantly lower in the bleeding group compared with non-bleeding group only at the 16th day of the cycle. These differences were significant, even though the values of estradiol and endometrial thickness remained in the normal range.

SP therapy can reduce the values of estradiol and the endometrial thickness in patients with PCOS compared with pretreatment, but PCOS patients with bleeding had pretreatment estradiol values lower than the patients who did not complain of this side effect. Intermenstrual abnormalities may represent the low estrogen impregnation of endometrium due to SP, whose mechanism is complex, involving several factors, such as the effects of some metabolites of SP on estradiol and progesterone production, on their receptors, and the individual metabolism of SP in vivo.