Examkin

Question

Difficulty: MediumEndocrinology and Metabolism

A 3636-year-old male software engineer visits the clinic complaining of a 33-month history of constant sweating, a 55-kg (1111-lb) unintended weight loss, and frequent bowel movements. He also mentions a new onset of dull, constant headaches and occasionally bumping into doorframes on his sides over the past few weeks. His temperature is 37.2∘C37.2^\circ\text{C} (99.0∘F99.0^\circ\text{F}), blood pressure is 145/85 mmHg145/85 \text{ mmHg}, and pulse is 105/min105/\text{min}. Physical examination reveals a mild resting tremor, moist skin, and a diffusely enlarged, non-tender thyroid gland without palpable nodules. Extraocular movements are intact, and there is no proptosis.

Laboratory studies are obtained and reveal the following:

Laboratory TestResultReference Range
Thyroid-stimulating hormone (TSH)5.2μU/mL5.2 \mu\text{U/mL}0.4−4.0μU/mL0.4 - 4.0 \mu\text{U/mL}
Free thyroxine (T4)3.1 ng/dL3.1 \text{ ng/dL}0.9−1.7 ng/dL0.9 - 1.7 \text{ ng/dL}
Free triiodothyronine (T3)6.5 pg/mL6.5 \text{ pg/mL}2.0−4.4 pg/mL2.0 - 4.4 \text{ pg/mL}

Which of the following is the most appropriate next step in the evaluation of this patient's condition?

  1. Magnetic resonance imaging of the brainAnswer
  2. B
    Measurement of thyroid-stimulating immunoglobulins
  3. C
    Radioactive iodine uptake scan
  4. D
    Measurement of serum thyroglobulin
  5. E
    Ultrasound of the thyroid gland

Answer

Magnetic resonance imaging of the brain
This patient presents with clinical signs of hyperthyroidism (weight loss, tachycardia, tremor, goiter) and bitemporal hemianopsia (evidenced by bumping into doorframes on his sides), suggesting a mass compressing the optic chiasm. His laboratory results show elevated free T4 and free T3 with an inappropriately elevated TSH. In primary hyperthyroidism, the TSH should be severely suppressed due to negative feedback. The lack of TSH suppression in the presence of elevated thyroid hormones indicates a central etiology, specifically a TSH-secreting pituitary adenoma. The most appropriate next step to confirm the anatomical presence of this pituitary macroadenoma is magnetic resonance imaging of the brain.

Step-by-Step Solution

1
Identify the clinical syndrome
The patient demonstrates classic signs of thyrotoxicosis, including weight loss, tachycardia, heat intolerance, tremor, and goiter.
Recognizing the broad clinical picture is required to interpret the laboratory results effectively.
2
Interpret the laboratory findings
Elevated free T4 and free T3 confirm thyrotoxicosis, while the TSH is inappropriately elevated.
In primary hyperthyroidism, the TSH should be suppressed via negative feedback. An elevated TSH paired with elevated thyroid hormones indicates secondary (central) hyperthyroidism.
3
Correlate lab findings with additional clinical clues
The patient's headaches and tendency to bump into doorframes (suggesting bitemporal hemianopsia) point to an intracranial mass compressing the optic chiasm.
This localizes the source of the secondary hyperthyroidism to a pituitary adenoma.
4
Determine the next diagnostic step
Brain imaging is required.
To confirm the anatomical presence and extent of a TSH-secreting pituitary adenoma, magnetic resonance imaging of the brain is the gold standard.

Key Concept

Diagnosis of secondary hyperthyroidism caused by a TSH-secreting pituitary adenoma
Rate this question

Topics

Endocrinology and Metabolism

More questions from this topic