Symptoms of Lean PCOS
Lean PCOS presents with the same core symptoms as obese PCOS—menstrual irregularities, hyperandrogenism, and polycystic ovarian morphology—but with less pronounced metabolic derangements and a higher body fat percentage compared to weight-matched healthy controls. 1, 2
Core Clinical Features
Menstrual Dysfunction
- Oligomenorrhea or amenorrhea due to chronic anovulation is the hallmark menstrual presentation 1, 3, 4
- Cycle length >35 days strongly suggests chronic anovulation 4
- Low mid-luteal phase progesterone levels confirm anovulation 1, 3
- Menstrual irregularities persist beyond the normal 2-3 year post-menarche adjustment period 4
Hyperandrogenic Manifestations
- Hirsutism develops gradually and is the most common androgenic symptom, intensifying with any weight gain 4
- Acne, particularly severe or treatment-resistant acne (including isotretinoin-resistant cases), occurs in up to 40% of women who will develop PCOS 4
- Alopecia with variable patterns: vertex, crown, or diffuse hair loss in mild cases; bitemporal recession and frontal hairline loss in more severe hyperandrogenemia 4
- Elevated free testosterone levels (more sensitive than total testosterone) confirm biochemical hyperandrogenism 4
Ovarian Morphology
- Polycystic ovaries on ultrasound showing ≥25 small follicles (2-9 mm diameter) in the whole ovary using modern ultrasound equipment 4
- Ovarian volume ≥10 mL indicates increased ovarian size 4
- Thickening of ovarian stroma may be present 1
Metabolic and Hormonal Profile
Insulin Resistance (Present Despite Lean Body Habitus)
- Insulin resistance is inherent in PCOS independent of obesity, affecting lean women with PCOS 3, 2
- Fasting glucose/insulin ratio >4 suggests reduced insulin sensitivity 1, 3
- Hyperinsulinemia drives androgen excess even in lean phenotype 3, 5
- Metabolic derangements are less obvious compared to obese PCOS but still present 2
Hormonal Abnormalities
- Elevated LH with LH/FSH ratio >2 due to accelerated GnRH pulsatility 1, 3
- Elevated testosterone (free testosterone preferred for diagnosis) 3, 4
- Lower sex hormone-binding globulin (SHBG) levels compared to healthy controls, though higher than in obese PCOS 1
- Elevated anti-Müllerian hormone levels 4
Body Composition Differences
- Higher body fat percentage than weight-matched healthy controls despite normal BMI 1
- This distinguishes lean PCOS from functional hypothalamic amenorrhea (FHA), where body fat percentage is typically low 1
Associated Symptoms and Complications
Reproductive Issues
- Infertility due to anovulation 1, 4, 6
- Increased risk of endometrial hyperplasia and endometrial cancer (at least twofold increased risk) due to unopposed estrogen from chronic anovulation 4, 6
Metabolic Risks (Present Even in Lean Phenotype)
- Increased risk of type 2 diabetes (31-40% develop glycemic intolerance) 5, 6
- Dyslipidemia 6, 7
- Increased cardiovascular disease risk with endothelial dysfunction 3, 6
- Metabolic syndrome features, though less pronounced than in obese PCOS 2
Psychological Manifestations
- Increased risk of depression requiring screening 6
- Emotional stress related to hirsutism, infertility, and hormonal disturbances 1
- Increased odds of eating disorders including binge eating disorder 1
Other Complications
Critical Diagnostic Distinction
Lean PCOS must be differentiated from functional hypothalamic amenorrhea with polycystic ovarian morphology (FHA-PCOM), as both present with oligomenorrhea and polycystic ovaries 1. Key distinguishing features include:
- FHA patients have low insulin levels and normal insulin sensitivity, while lean PCOS patients have insulin resistance 1
- FHA patients have lower body fat percentage, while lean PCOS patients have higher body fat than weight-matched controls 1
- FHA typically has history of excessive exercise, caloric restriction, or significant stress 1
- FHA patients have lower SHBG than lean PCOS patients 1