What are the possible causes of amenorrhea in a 16‑year‑old girl?

Causes of Amenorrhea in a 16-Year-Old Girl

Amenorrhea in a 16-year-old requires systematic evaluation to distinguish between anatomic abnormalities, hypothalamic-pituitary dysfunction, ovarian disorders, and other endocrine causes, with pregnancy being the first consideration to exclude. 1

Primary Diagnostic Categories

The causes can be organized into three main pathophysiologic categories based on gonadotropin status:

1. Eugonadotropic Eugonadism (Normal FSH, Normal Estrogen)

These are anatomic/outflow tract disorders:

• Müllerian agenesis (Mayer-Rokitansky-Küster-Hauser syndrome) - Most common anatomic cause (33.8% in one series), typically diagnosed later (median age 20 years) 2
• Imperforate hymen - Presents earlier (median age 14 years) with cyclic pelvic pain and a bluish bulge on external exam 1, 2
• Transverse vaginal septum
• Asherman syndrome (rare in adolescents without prior instrumentation)
• Androgen insensitivity syndrome - 46,XY karyotype with absent uterus, normal breast development 3

2. Hypergonadotropic Hypogonadism (High FSH >25 IU/L, Low Estradiol)

These indicate ovarian/gonadal failure:

• Turner syndrome (45,X or mosaic) - Most common chromosomal cause 4, 3
• Primary ovarian insufficiency - Idiopathic, autoimmune oophoritis, or iatrogenic (chemotherapy/radiation) 5, 4
• 46,XY disorders of sex development (gonadal dysgenesis) - 28.8% of cases in some series 4, 2
• 17α-hydroxylase deficiency (rare enzymatic defect) 4

3. Hypogonadotropic Hypogonadism (Low/Normal FSH, Low Estradiol)

These reflect hypothalamic-pituitary dysfunction:

• Functional hypothalamic amenorrhea (FHA) - Associated with:

  • Energy deficit from restrictive eating, excessive exercise (>12 hours/week), or low body weight 1
  • Psychological stress, perfectionism, high need for social approval 1
  • Presents with bradycardia, cool extremities, hypercarotenemia 1

• Congenital hypogonadotropic hypogonadism - Including Kallmann syndrome (with anosmia/hyposmia) 1, 4

• Constitutional delay of growth and puberty 4

• Hyperprolactinemia - Check for galactorrhea, visual field defects, headaches 1, 6

• Pituitary/hypothalamic tumors - Craniopharyngioma, prolactinoma 4

4. Normogonadotropic Causes (Normal FSH, Variable Estrogen)

• Polycystic ovary syndrome (PCOS) - Most common cause of secondary amenorrhea; look for acne, hirsutism, acanthosis nigricans, elevated LH:FSH ratio 1, 6, 3
• Chronic systemic diseases - Inflammatory bowel disease, celiac disease, chronic kidney disease 1, 4
• Thyroid disorders - Both hypothyroidism and hyperthyroidism 1, 6
• Late-onset congenital adrenal hyperplasia - Elevated 8 AM 17-hydroxyprogesterone, virilization 1, 7
• Cushing syndrome - Weight gain, striae, hypertension 8

Critical Evaluation Approach

History Must Include:

• Menstrual history: age of thelarche, presence/absence of prior menses
• Weight changes, dietary patterns, binge/purge behaviors, exercise intensity and duration 1
• Psychological stressors, perfectionism traits, mood disorders 1
• Galactorrhea, headaches, visual changes, anosmia 1
• Hirsutism, acne, voice deepening 1
• Cyclic pelvic pain (suggests outflow obstruction) 1
• Medications (antipsychotics, antidepressants, opioids) 1
• Family history of eating disorders, delayed puberty, premature menopause 1

Physical Examination Must Assess:

• Height, weight, BMI trends
• Tanner staging of breast and pubic hair development
• External genitalia: look for imperforate hymen (bluish bulge), clitoromegaly, vaginal atrophy 1
• Hyperandrogenic signs: acne, hirsutism, male pattern alopecia 1
• Acanthosis nigricans (insulin resistance/PCOS) 1
• Galactorrhea, thyromegaly 1
• Bradycardia, cool extremities, hypercarotenemia (FHA) 1
• Visual field testing, fundoscopy (pituitary lesions) 1

Initial Laboratory Testing (All Patients):

Per Endocrine Society guidelines 1:

1. β-hCG (pregnancy test - mandatory first step)
2. FSH, LH, estradiol - Pattern determines category
3. Prolactin
4. TSH, free T4
5. AMH (reflects ovarian reserve) 1
6. Complete blood count, comprehensive metabolic panel 1
7. ESR/CRP if chronic illness suspected 1

Additional Testing Based on Initial Results:

• If hyperandrogenic signs present: Total testosterone, DHEA-S, 8 AM 17-hydroxyprogesterone 1
• If FSH >25 IU/L (twice, 1 month apart): Karyotype to identify Turner syndrome or 46,XY DSD 5, 3
• If primary amenorrhea with normal breast development: Pelvic ultrasound or MRI to evaluate uterine presence and anatomy 1
• If very low/undetectable LH and FSH: Brain MRI to exclude pituitary/hypothalamic lesions 1

Key Clinical Pitfalls

Critical Warning: In patients on combined oral contraceptives or progestins with antigonadotropic effects, FSH will be falsely suppressed. Discontinue for ≥3 months before retesting 5.

Important Distinction: FHA can mask underlying PCOS. Women with normoandrogenic oligomenorrhea, polycystic ovary morphology, and elevated AMH may develop hyperandrogenic PCOS when hypothalamic function normalizes with weight gain 1. These patients require closer monitoring.

Age-Specific Consideration: At age 16, if menarche has not occurred and it has been >3 years since thelarche, this constitutes primary amenorrhea requiring full evaluation 9, 10.

Bone Health Priority: FHA, primary ovarian insufficiency, and prolonged hypogonadism from any cause result in irreversible bone loss during this critical period of peak bone mass accrual 1. This represents significant long-term morbidity requiring urgent intervention.