Amenorrhea Pathophysiology

Mechanisms of Amenorrhea

The American College of Obstetricians and Gynecologists notes that low energy availability disrupts the hypothalamic-pituitary-gonadal axis, altering luteinizing hormone pulsatility, leading to menstrual dysfunction manifested as oligo-amenorrhea 1
Chronic stress causes functional reduction in pulsatile gonadotropin-releasing hormone (GnRH) secretion from the hypothalamus, decreasing luteinizing hormone (LH) and follicle-stimulating hormone (FSH) pulses, preventing ovulation and menstruation 2
Kisspeptin neurons serve as a critical bridge between the stress response system and the reproductive axis, mediating the effects of stress on menstruation 2
The Endocrine Society recommends that stress hormones, particularly cortisol and catecholamines, directly suppress the GnRH pulse generator 2
These hormonal alterations result in decreased estradiol and progesterone levels, not increased 1

The European Society of Human Reproduction and Embryology states that PCOS is the most common cause of irregular menstrual cycles, affecting approximately 4-6% of women in the general population 2
The pathogenesis of PCOS involves accelerated GnRH pulse secretion, insulin resistance, hyperinsulinemia, and metabolic dysregulation 3
Reproductive axis abnormalities manifest as hypersecretion of LH, hyperactivity of ovarian stromal cells, and hypofunction of the FSH-granulosa cell axis, resulting in hyperandrogenism, hirsutism, follicular arrest, and anovulation 3
Laboratory findings typically show an LH:FSH ratio >2, which strongly suggests PCOS 2

The American College of Obstetricians and Gynecologists notes that hyperprolactinemia represents approximately 20% of secondary amenorrhea cases 1, 2
Generalized seizures and seizures involving the temporal lobes lead to postictal elevations of prolactin 3
Functional hyperprolactinemia causes polymenorrhea, oligomenorrhea, or amenorrhea, subfertility, galactorrhea, and hirsutism 3

The Endocrine Society states that primary ovarian insufficiency is characterized by elevated FSH and LH levels 1
Hypothalamic amenorrhea, also called hypogonadotropic hypogonadism, was found in 12% of 50 consecutive women with temporal lobe epilepsy, while it is estimated to affect only 1.5% of the general population 3
Hypothalamic amenorrhea is associated with altered secretion of hypophysial gonadotropins with low LH levels 3

Both hypothyroidism and hyperthyroidism can cause menstrual irregularities by affecting the hypothalamic-pituitary-ovarian axis 2

Advanced liver disease causes menstrual irregularities in >25% of women through altered estrogen metabolism and disruption of the hypothalamic-pituitary axis 2

Epilepsy can directly affect the hypothalamic-pituitary axis and increase the risk of amenorrhea 1
Many older antiepileptic medications, including carbamazepine, phenobarbital, and phenytoin, induce the degradation of steroid hormones dependent on hepatic cytochrome P450 and the production of sex hormone-binding globulin (SHBG), thus reducing serum concentrations of biologically active sex hormones 3

Approximately 40-47% of women with functional hypothalamic amenorrhea have polycystic ovarian morphology (AHF-PCOM), which can be misdiagnosed as PCOS 2
This distinction is critical because AHF-PCOM requires correction of the energy deficit as primary treatment, not therapy targeted at PCOS 2

The decrease in bone mineral density and increased risk of stress fractures are important complications of amenorrhea, particularly in hypoestrogenic states 1, 4
In the context of oligo-amenorrhea with low estrogen, bone microarchitecture is negatively affected, leading to decreased trabecular number and cortical thickness 1
When estrogen levels are aberrantly subphysiologic, osteoclastic activity predominates, and bone mass is lost 1

Low energy availability disrupts GnRH pulsatility from the hypothalamus, which directly suppresses pituitary LH pulse secretion, preventing ovulation and causing oligo-amenorrhea, as reported by the Sports Medicine journal 5
Pituitary dysfunction leading to hypoestrogenism causes accelerated bone loss through increased osteoclast activity, according to the Sports Medicine journal 5

The American College of Sports Medicine recommends that patients with amenorrhea undergo DXA scanning if amenorrhea extends beyond 6 months, regardless of age, to assess bone health 5