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Zorluk: OrtaEndocrinology and Metabolism

A 35-year-old woman comes to the clinic for evaluation of profound fatigue, a 6-kg (13.2-lb) weight gain, and feeling constantly cold over the past 8 months. She also reports that her menstrual periods have been absent for the past 6 months. Her last pregnancy was 4 years ago and was uncomplicated. She takes no medications. Vital signs show a blood pressure of 110/70 mm Hg and a heart rate of 56/min. Physical examination reveals dry, pale skin and delayed relaxation of the deep tendon reflexes. A urine pregnancy test is negative. Laboratory evaluation shows:

Laboratory TestResultReference Range
TSH1.2 µU/mL0.5–5.0 µU/mL
Free T40.4 ng/dL0.9–1.7 ng/dL

Which of the following is the most likely underlying mechanism for this patient's clinical presentation?

  1. Compression of the anterior pituitary by a benign neoplasmCevap
  2. B
    Autoimmune destruction of the thyroid gland
  3. C
    Excessive ovarian androgen production leading to chronic anovulation
  4. D
    Physiologic increase in circulating hormone-binding globulins
  5. E
    Inadequate dietary consumption of iodine

Cevap

The most likely mechanism is compression of the anterior pituitary by a benign neoplasm (causing central hypothyroidism and hypogonadism).
The patient's clinical presentation of fatigue, weight gain, cold intolerance, bradycardia, and delayed deep tendon reflexes is highly characteristic of hypothyroidism. In a healthy hypothalamic-pituitary-thyroid (HPT) axis, a drop in free T4 removes negative feedback on the pituitary, resulting in a compensatory elevation in TSH. In this patient, the free T4 is clearly low, but the TSH is inappropriately normal. This discordance indicates a failure at the level of the pituitary gland or hypothalamus, known as central (or secondary) hypothyroidism. The concomitant presentation of amenorrhea suggests multiple pituitary axes are involved (panhypopituitarism). The most common cause of panhypopituitarism in an adult is a non-functioning pituitary adenoma compressing the anterior pituitary gland.

Adım Adım Çözüm

1
Analyze the clinical presentation.
The patient has symptoms of a hypometabolic state (fatigue, weight gain, cold intolerance, bradycardia, delayed reflexes) and amenorrhea.
Identifying the affected organ systems guides the interpretation of the laboratory data.
2
Interpret the thyroid laboratory profile.
Free T4 is overtly low, but the TSH is within the normal reference range (1.2 µU/mL).
A healthy pituitary should respond to a low T4 by secreting massive amounts of TSH. An inappropriately normal TSH in the face of low T4 indicates central (secondary) hypothyroidism.
3
Synthesize the findings to determine the underlying mechanism.
The combination of central hypothyroidism and secondary amenorrhea (hypogonadotropic hypogonadism) strongly points to a structural pituitary lesion, such as a non-functioning pituitary adenoma.
Mass effect from a benign neoplasm compresses the thyrotroph and gonadotroph cells, leading to decreased secretion of multiple anterior pituitary hormones.

Anahtar Kavram

Central (secondary) hypothyroidism is characterized by a low free T4 and an inappropriately normal or low TSH. When combined with other pituitary hormone deficiencies (e.g., amenorrhea), a structural pituitary lesion should be highly suspected.
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Endocrinology and Metabolism

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