Pathophysiology of PCOS
PCOS is fundamentally a disorder of hyperandrogenic chronic anovulation driven by the interaction of altered hypothalamic-pituitary-ovarian function and concomitant hyperinsulinemia/insulin resistance, which together promote androgen excess. 1, 2
Core Pathophysiologic Mechanisms
The pathogenesis involves several interconnected abnormalities:
Neuroendocrine Dysfunction
- Accelerated pulsatile GnRH secretion from the hypothalamus drives the reproductive axis abnormalities 1
- This results in hypersecretion of luteinizing hormone (LH) with relative hypofunction of the FSH-granulosa cell axis 1
- The hypothalamus demonstrates reduced feedback response to circulating sex steroids, perpetuating abnormal gonadotropin secretion 3
Ovarian Dysfunction
- Ovarian theca stromal cell hyperactivity produces excess androgens 1
- Hypofunction of the FSH-granulosa cell axis leads to follicular arrest and failure of normal follicle maturation 1
- This creates the characteristic polycystic ovarian morphology with >10 peripheral cysts (2-8 mm diameter) and thickened ovarian stroma 1
- The arrested follicles contribute to ovarian acyclicity and chronic anovulation 1
Metabolic Dysregulation
- Insulin resistance and hyperinsulinemia are central to PCOS pathophysiology 1, 2
- Insulin resistance occurs in multiple target tissues, not just reproductive organs 3
- Hyperinsulinemia directly stimulates ovarian androgen production and reduces sex hormone binding globulin (SHBG) production, increasing free androgen levels 1
- This creates a vicious cycle where hyperandrogenism and insulin resistance exacerbate one another 4
Clinical Manifestations
The reproductive axis abnormalities manifest as:
- Hyperandrogenism with elevated testosterone (>2.5 nmol/L) 1
- Hirsutism from excess androgen effects 1
- Chronic anovulation indicated by low mid-luteal phase progesterone (<6 nmol/L) 1
- Oligomenorrhea or amenorrhea 1
Important Distinctions
PCOS must be distinguished from isolated polycystic ovaries, which represent polycystic morphology without symptoms, pathological signs, or hormonal abnormalities 1. Isolated polycystic ovaries occur in 17-22% of the general population, whereas only some women with polycystic ovaries develop full PCOS with chronic oligomenorrhea/amenorrhea and elevated androgens 1.
Etiologic Factors
The disorder is highly heritable with familial clustering, where both female and male relatives can show metabolic stigmata 3. However, environmental factors make a larger contribution than genetic factors 4:
- Weight gain is a major trigger for PCOS development 1
- Intrauterine environment during prenatal period 4
- Follicular microenvironment alterations 4
- Lifestyle factors after birth 4
- Environmental toxicants and stress 5
Metabolic Consequences
The pathophysiology creates downstream metabolic dysregulation 1 with:
- Reduced insulin sensitivity (glucose/insulin ratio >4) 1
- Increased risk for type 2 diabetes 2
- Elevated cardiovascular disease risk, now recognized as a cardiovascular disease risk-enhancing factor 6
- Association with obesity, metabolic syndrome, and sleep apnea 2
Heterogeneity
PCOS pathophysiology is heterogeneous and shaped by the interaction of reproductive dysfunction and metabolic disorders 4. The phenotype can vary by race/ethnicity and is exacerbated by obesity 3. The complex bidirectional relationship between obesity and PCOS means obesity is both increased in PCOS, causal of PCOS, and exacerbates clinical features 2.