A 16-year-old girl presents to the gynaecology outpatient department with her mother, reporting that she has never menstruated. On examination, she is 165 cm tall, has normal breast development (Tanner stage 5), and normal external genitalia. Pelvic ultrasound reveals a normal uterus and ovaries with multiple small follicles. Serum FSH is 45 mIU/mL, LH is 38 mIU/mL, and oestradiol is <20 pg/mL. What is the most likely diagnosis?

Explanation

## Diagnosis: Primary Ovarian Insufficiency (POI) ### Clinical Features Supporting POI - **Age of presentation:** 16 years (primary amenorrhea) - **Breast development:** Normal (Tanner stage 5) — indicates prior oestrogen exposure and intact hypothalamic-pituitary-ovarian axis responsiveness - **Pelvic ultrasound:** Normal uterus and ovaries with follicles — rules out anatomical abnormalities - **Hormonal pattern:** Markedly elevated FSH (45 mIU/mL) and LH (38 mIU/mL) with low oestradiol (<20 pg/mL) ### Pathophysiology **Key Point:** Primary ovarian insufficiency is characterized by loss of ovarian follicular reserve and function before age 40, resulting in hypergonadotropic hypogonadism (high FSH/LH, low oestradiol). The elevated gonadotropins reflect the pituitary's attempt to stimulate failing ovaries. Normal breast development indicates that oestrogen was produced earlier in puberty, distinguishing this from complete gonadal dysgenesis. ### Differential Diagnosis Table | Feature | POI | Müllerian Agenesis | Gonadal Dysgenesis | Hypothalamic Amenorrhea | | --- | --- | --- | --- | --- | | **Breast development** | Normal/present | Normal/present | Absent/sparse | Normal/present | | **FSH level** | High (>40 mIU/mL) | Normal | High (>40 mIU/mL) | Low/normal | | **Uterus on USS** | Present | Absent | Present | Present | | **Ovarian follicles** | Present (few) | Normal | Absent (streak) | Normal | | **Oestradiol** | Low | Normal | Low | Low | **High-Yield:** The combination of **primary amenorrhea + normal breast development + high FSH + normal uterus = POI** until proven otherwise. ### Clinical Pearl POI can be associated with autoimmune conditions (thyroiditis, adrenalitis), chromosomal mosaicism (45,X/46,XX), or idiopathic follicle depletion. Karyotyping and thyroid screening are recommended in all cases of POI. ### Management Implications - Hormone replacement therapy (oestrogen + progesterone) for bone health and cardiovascular protection - Fertility counselling: spontaneous pregnancy possible in ~5–10% of cases; assisted reproductive technology (ART) with donor oocytes for most - Screen for associated autoimmune and metabolic conditions