A 16-year-old girl is brought to her pediatrician for a well-child visit

A 16-year-old girl is brought to her pediatrician for a well-child visit. During the interview, she notes that she has not yet had a period, although she notes that she has been exercising more often during the past few months. On exam, she has a BMI of 22, breasts are Tanner stage I, and measured follicle stimulating hormone (FSH) level is 167 mIU/mL (normal 0.3-10 mIU/mL). Which of the following is the next best step?

  1. Measure serum thyroid stimulating hormone

  2. Measure serum electrolytes and initiate refeeding protocol

  3. Measure serum cortisol levels

  4. Prescribe a combined oral contraceptive pill

  5. Karyotyping

View Explanation

This patient’s clinical presentation is consistent with Turner’s Syndrome (TS), which can be diagnosed by karyotyping.

TS is the most common cause of primary amenorrhea with an elevated follicle stimulating hormone (FSH). TS is characterized by lack of a second sex X-chromosome, such that patients have the karyotype 45, X. Patients with TS typically undergo ovarian failure early in childhood and can have a normal or underdeveloped uterus. Other abnormal features include minimal breast development and wide-set nipples. Estrogen replacement therapy can be used to increase development of secondary sex characteristics.

Illustration A lists the major features of TS. Illustration B is a photo showing the classic appearance of children with TS.