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Difficulty: MediumMenstrual Cycle Abnormalities and Contraception

A 15-year-old girl is brought to the clinic by her parents due to the absence of menarche. She reports no cyclical lower abdominal pain. A urine beta-hCG test obtained in the clinic is negative. Her height is at the 5th percentile for her age, and her weight is at the 40th percentile. Vital signs are within normal limits. Physical examination reveals Tanner stage 1 breast development and Tanner stage 1 pubic hair. She has a broad chest with widely spaced nipples and a low posterior hairline. Arrange the following diagnostic steps in the most appropriate sequential order to evaluate and manage this patient's condition.

  1. 1Perform a pelvic ultrasonography to confirm the presence of a uterus
  2. 2Measure serum follicle-stimulating hormone (FSH) level
  3. 3Perform a karyotype analysis
  4. 4Obtain a transthoracic echocardiogram

Answer

The correct sequence is: 1) pelvic ultrasonography, 2) serum FSH measurement, 3) karyotype analysis, 4) transthoracic echocardiogram.
The diagnostic evaluation for primary amenorrhea follows a rigid stepwise algorithm. After ruling out pregnancy (beta-hCG is negative), the first step is a pelvic ultrasound to confirm the presence of a uterus. If the uterus is present and the patient lacks secondary sexual characteristics (Tanner stage 1 breasts), serum FSH is measured next to distinguish between hypergonadotropic hypogonadism (ovarian failure) and hypogonadotropic hypogonadism (central defect). In a patient with short stature, a broad chest, and low hairline, the FSH will be elevated. The next step is a karyotype analysis to definitively diagnose Turner syndrome (45,X). Upon confirming Turner syndrome, a transthoracic echocardiogram must be obtained to screen for associated cardiovascular defects, such as a bicuspid aortic valve or coarctation of the aorta.

Step-by-Step Solution

1
Confirm the presence of reproductive anatomy
Perform a pelvic ultrasonography
In primary amenorrhea, identifying whether Mullerian structures (the uterus) are present determines the correct diagnostic branch of the algorithmic pathway.
2
Differentiate central versus peripheral hypogonadism
Measure serum FSH level
With a uterus present and absent breast development, an FSH level determines if the cause is primary ovarian failure (high FSH) or a hypothalamic/pituitary defect (low/normal FSH).
3
Diagnose the specific genetic etiology
Perform a karyotype analysis
An elevated FSH confirms hypergonadotropic hypogonadism. In a patient with short stature and specific physical stigmata, a karyotype provides the definitive diagnosis of Turner syndrome.
4
Screen for life-threatening comorbidities
Obtain a transthoracic echocardiogram
Once Turner syndrome is diagnosed, immediate screening for highly prevalent and potentially fatal cardiovascular defects is required.

Key Concept

Stepwise evaluation and management of primary amenorrhea
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Topics

Menstrual Cycle Abnormalities and Contraception

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