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Difficulty: MediumMenstrual Cycle Abnormalities and Contraception

A 32-year-old woman comes to the office due to the absence of menstrual periods for the past 9 months. Her menarche occurred at age 13, and her menses were previously regular, occurring every 28 days and lasting 5 days. Over the last year, she has experienced progressive fatigue, cold intolerance, and a 5-kg (11-lb) weight gain despite a decreased appetite. She has no headaches, visual disturbances, or galactorrhea. Her medical history is unremarkable, and she takes no medications. Vital signs show a blood pressure of 102/64 mmHg and a pulse of 54/min. Physical examination reveals dry, cool skin and a delayed relaxation phase of the deep tendon reflexes. Pelvic examination is normal with no clitoromegaly. A urine pregnancy test is negative.

Laboratory evaluation shows:
Thyroid-stimulating hormone (TSH): 1.3 mIU/L (Normal: 0.5–5.0 mIU/L)
Free thyroxine (T4): 0.4 ng/dL (Normal: 0.8–1.8 ng/dL)
Prolactin: 12 ng/mL (Normal: < 25 ng/mL)
Follicle-stimulating hormone (FSH): 3 mIU/mL (Normal: 5–20 mIU/mL)
Luteinizing hormone (LH): 2 mIU/mL (Normal: 5–20 mIU/mL)

Which of the following is the most appropriate next step in management?

  1. Magnetic resonance imaging of the pituitary glandAnswer
  2. B
    Initiation of levothyroxine therapy
  3. C
    Measurement of early morning serum 17-hydroxyprogesterone
  4. D
    Administration of a 10-day course of medroxyprogesterone acetate
  5. E
    Endometrial biopsy

Answer

Magnetic resonance imaging of the pituitary gland
The patient presents with secondary amenorrhea, fatigue, weight gain, and delayed deep tendon reflexes, which strongly suggest hypothyroidism. However, her laboratory results show a low free T4 level paired with an inappropriately normal TSH. In primary hypothyroidism, the intact pituitary responds to low T4 by increasing TSH production. The absence of this normal feedback response (a normal TSH despite low T4) indicates central (secondary) hypothyroidism. Furthermore, her amenorrhea is accompanied by low-normal FSH and LH levels, pointing to concurrent hypogonadotropic hypogonadism. The presence of multiple anterior pituitary hormone deficiencies (panhypopituitarism) raises high suspicion for a pituitary or hypothalamic disorder, such as a non-functioning pituitary macroadenoma. Therefore, the most appropriate next step in management is to perform magnetic resonance imaging (MRI) of the brain and pituitary gland to evaluate for a structural lesion.

Step-by-Step Solution

1
Interpret the clinical presentation and initial laboratory findings.
The patient has secondary amenorrhea, clinical signs of hypothyroidism, a low free T4, and an inappropriately normal TSH.
To differentiate between primary and secondary (central) causes of endocrine dysfunction.
2
Identify the underlying pathophysiologic process.
The combination of central hypothyroidism and hypogonadotropic hypogonadism indicates panhypopituitarism.
Multiple anterior pituitary hormone deficiencies suggest a structural lesion in the pituitary or hypothalamus.
3
Determine the most appropriate next step in management.
Magnetic resonance imaging of the pituitary gland is indicated.
To evaluate for a compressive mass, such as a non-functioning pituitary macroadenoma, causing the hypopituitarism.

Key Concept

Evaluation of secondary amenorrhea and panhypopituitarism
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Topics

Menstrual Cycle Abnormalities and Contraception

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