Question

The Women’s Health Nurse Practitioner evaluated Sara, a 17-year old female. Sara has not had a menstrual period for 6 months. Her history reveals that menarche occurred at the age of 12 years, and her menses were regular at 28-day intervals until they became irregular 1 year ago. Sara is a member of her high school gymnastics team. She has been spending long hours training with the team, as she hopes to get a gymnastic scholarship at her “dream” university – the University of California, Los Angeles. In addition, she has ramped up her aerobic exercise program to strengthen her endurance. She states that she often does not have time to eat or is simply too tired to eat after training and getting her schoolwork done. She often relies on energy bars. She denies abdominal pain or bloating. Sara appears emaciated. She is 5 ft 4 in tall and weighs 88 lb; BMI is 15 kg/m2. Her pulse is 54/min, and blood pressure is 80/50 mm Hg. The rest of her physical exam is non-remarkable. Impression - The Nurse Practitioner suspects secondary amenorrhea(i.e., the absence of 3 to 12 consecutive menstrual periods after menarche). The secondary amenorrhea is most likely due to her exercise program, which has increased in intensity and duration over the last 6 months. It is also possible that Sara is not eating enough, given her high energy expenditure. To determine the cause of her amenorrhea, laboratory tests are ordered. Laboratory Test Results Pregnancy test negative LH Below normal FSH Below normal Estradiol Below normal Serum total calcium 7.8 mg/dl (normal range = 8.6-10.3 mg/dl) Serum ionized calcium 3.9 mg/dl (normal range = 4.4-5.2 mg/dl) Serum vitamin D, 25 hydroxy 25 ng/ml (normal range = 30-80 ng/ml) Serum PTH Increased above normal Follow Up Tests: Given that Sara’s serum calcium and vitamin D results were below normal, Sara had a bone density (DXA scan). Results revealed a Z score = -1 (lower than normal bone density). Given the low LH and FSH, Sara was tested with a priming dose of intravenous pulsatile GnRH (1-2 mg/90 minutes). Results showed normal levels of LH and FSH, in response to GnRH.

1. Considering Sara’s level of PTH, describe what adaptive response might be taking place within Sara’s bone (i.e., focus on the inter-relationship between the cells within the osteon)? How does this relate to her bone density results? How does estrogen affect bone physiology?

Answer 1