Differential Diagnosis for Amenorrhea in a 16-year-old Girl
- Single most likely diagnosis:
- Müllerian agenesis (Mayer-Rokitansky-Küster-Hauser syndrome): This condition is characterized by the congenital absence of the uterus and upper part of the vagina in individuals with a 46,XX karyotype. The presence of normal ovarian function (indicated by Tanner stage 4 breast development and pubic and axillary hair) and the absence of a uterus on pelvic ultrasonography strongly support this diagnosis.
- Other Likely diagnoses:
- Anorexia athletica or athletic amenorrhea: Although the patient's weight is at the 20th percentile and she is intensely involved in sports, her normal vital signs and the absence of other symptoms suggestive of an eating disorder make this less likely. However, it's still a consideration given her athletic activities and low weight percentile.
- Polycystic ovary syndrome (PCOS): PCOS could explain amenorrhea, but the absence of a uterus and the presence of normal-sized ovaries with no mention of cysts on ultrasonography make this less likely. PCOS typically presents with hyperandrogenism, ovulatory dysfunction, and polycystic ovaries.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed):
- Androgen insensitivity syndrome (AIS): This is a condition where an individual with a 46,XY karyotype is resistant to androgen, leading to the development of female external genitalia despite the presence of testes. It's crucial to rule out AIS because it involves the presence of testes, which can increase the risk of testicular cancer if not removed. The absence of a uterus and the presence of normal breast development could suggest AIS, but the normal ovarian tissue seen on ultrasonography makes this less likely.
- Gonadal dysgenesis: This condition involves abnormal development of the gonads and can be associated with various karyotypic abnormalities. It's essential to consider because some forms can increase the risk of gonadal tumors.
- Rare diagnoses:
- Congenital adrenal hyperplasia: Although this condition can cause amenorrhea due to hormonal imbalances, it typically presents with symptoms of androgen excess and is less likely given the patient's presentation and normal ovarian function.
- Other genetic syndromes affecting the reproductive system: There are several rare genetic syndromes that can affect the development of the female reproductive system, leading to amenorrhea. These would be considered if the more common diagnoses are ruled out and genetic evaluation is pursued.