A 35-year-old woman comes to the clinic due to a 3-month history of constant anxiety, exce… — USMLE Step 2 CK

A $35$ -year-old woman comes to the clinic due to a $3$ -month history of constant anxiety, excessive sweating, unintended weight loss of $4.5$ kg ( $10$ lb), and frequent heart palpitations. She has no significant past medical history and takes no medications. Vital signs show a blood pressure of $138/78$ mm Hg and a heart rate of $114/min$ . Physical examination reveals a fine resting tremor in both hands, warm and diaphoretic skin, and a symmetrically enlarged, non-tender thyroid gland. There is no proptosis, extraocular muscle restriction, or pretibial myxedema.

Laboratory studies reveal:
Thyroid-stimulating hormone (TSH): $6.2 \mu U/mL$ (Normal: $0.4-4.0 \mu U/mL$ )
Free thyroxine (T4): $3.4 ng/dL$ (Normal: $0.9-2.4 ng/dL$ )
Total triiodothyronine (T3): $270 ng/dL$ (Normal: $80-200 ng/dL$ )
Urine human chorionic gonadotropin: Negative

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

Magnetic resonance imaging of the pituitary glandAnswer
B
Radioactive iodine uptake and scan
C
Measurement of thyroid-stimulating immunoglobulins
D
Ultrasound of the thyroid gland
E
Measurement of thyroid peroxidase antibodies

Answer

Magnetic resonance imaging of the pituitary gland

This patient presents with classic signs and symptoms of thyrotoxicosis, including weight loss, palpitations, tremor, and diaphoresis, along with a diffusely enlarged thyroid gland (goiter). Her laboratory results show elevated free T4 and total T3. In a normal physiologic state, these high levels of circulating thyroid hormones would strongly suppress pituitary TSH production via negative feedback. However, her TSH is inappropriately elevated (

6.2 \mu U/mL

). This pattern of hyperthyroidism with a non-suppressed (normal or elevated) TSH indicates a central etiology, most commonly a TSH-secreting pituitary adenoma (TSHoma). TSHomas secrete biologically active TSH that stimulates the thyroid gland to produce excess hormone, overcoming normal negative feedback mechanisms. The most appropriate next step in the evaluation of suspected central hyperthyroidism is magnetic resonance imaging (MRI) of the pituitary gland to visually identify the adenoma.

Step-by-Step Solution

Interpret the thyroid function laboratory results in the context of the patient's hypermetabolic symptoms.

The patient has elevated free T4 and T3 levels with clinical thyrotoxicosis, but her TSH is inappropriately elevated rather than suppressed.

Establishing whether the hyperthyroidism is primary (suppressed TSH) or secondary/central (non-suppressed TSH) dictates the diagnostic pathway.

Determine the anatomic origin of the pathology based on the absence of expected negative feedback.

The failure of high thyroid hormone levels to suppress TSH indicates central hyperthyroidism, which is most commonly caused by a TSH-secreting pituitary adenoma.

Normal pituitary physiology requires TSH to decrease when peripheral thyroid hormones are high.

Select the appropriate diagnostic imaging to confirm the etiology.

Magnetic resonance imaging (MRI) of the pituitary gland is the correct choice.

MRI provides the best visualization of the pituitary fossa and is required to anatomically identify the suspected adenoma.

Key Concept

Central hyperthyroidism (e.g., TSH-secreting pituitary adenoma) presents with clinical thyrotoxicosis, elevated thyroid hormones, and an inappropriately normal or elevated TSH. The next best step in evaluation is a pituitary MRI.

Question

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Topics

More questions from this topic