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Difficulty: EasyEndocrinology and Metabolism

An executive health screening is performed for a 45-year-old man who reports a 6-month history of significant fatigue, reduced libido, and a constant feeling of coldness. Physical examination shows a heart rate of 56/min56/min, normal blood pressure, and delayed relaxation of the deep tendon reflexes. Laboratory evaluation reveals:

Thyroid-stimulating hormone (TSH): 1.1μU/mL1.1 \mu U/mL (Normal: 0.4−4.0μU/mL0.4 - 4.0 \mu U/mL)
Free thyroxine (T4): 0.4ng/dL0.4 ng/dL (Normal: 0.9−1.7ng/dL0.9 - 1.7 ng/dL)

Which of the following additional findings is most likely to be present in this patient?

  1. A
    Elevated serum anti-thyroid peroxidase antibody titers
  2. B
    Enlarged, firm, and rubbery thyroid gland on palpation
  3. C
    Elevated serum luteinizing hormone concentration
  4. Decreased serum adrenocorticotropic hormone concentrationAnswer
  5. E
    Elevated serum thyroid-stimulating immunoglobulin levels

Answer

Decreased serum adrenocorticotropic hormone concentration
The patient's laboratory results (low free T4 with an inappropriately normal TSH) are diagnostic of central hypothyroidism, which is caused by a failure of the pituitary gland or hypothalamus to produce sufficient TSH. This is frequently due to a mass lesion such as a pituitary adenoma. When the anterior pituitary gland is compromised, other hormones are also frequently deficient (panhypopituitarism). Therefore, a decreased serum adrenocorticotropic hormone (ACTH) concentration, as well as decreased gonadotropins (LH, FSH) causing his reduced libido, would most likely be present.

Step-by-Step Solution

1
Interpret the thyroid function tests.
The patient has a low free T4 level, indicating hypothyroidism, but the TSH level is within the normal reference range.
To establish the primary hormonal abnormality.
2
Determine the etiology of the hypothyroidism based on the TSH response.
A low free T4 with an inappropriately normal (or low) TSH points to central (secondary) hypothyroidism, typically due to pituitary or hypothalamic dysfunction.
Primary hypothyroidism would present with an elevated TSH due to a lack of negative feedback on the intact pituitary gland.
3
Identify associated findings of pituitary dysfunction.
Patients with central hypothyroidism often have panhypopituitarism, which involves deficiencies in other anterior pituitary hormones, including adrenocorticotropic hormone (ACTH) and gonadotropins.
To predict what other clinical or laboratory abnormalities the patient might have.

Key Concept

Diagnosis of central hypothyroidism and recognition of associated panhypopituitarism
Estimated Time:1m 0s
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Topics

Endocrinology and Metabolism

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