Examkin

Soru

Zorluk: OrtaFormulating a Differential Diagnosis

A 28-year-old female medical resident presents to the clinic with a 4-week history of diarrhea, palpitations, heat intolerance, and a 44-kg (8.88.8-lb) weight loss. She states she has been under immense stress during her current intensive care unit rotation and admits to taking an over-the-counter "energy and metabolism booster" to help her stay awake. Her temperature is 37.2∘C37.2^\circ\text{C} (99.0∘F99.0^\circ\text{F}), blood pressure is 135/85135/85 mmHg, and pulse is 112112/min. Physical examination reveals a fine tremor in her outstretched hands, warm and moist skin, and brisk deep tendon reflexes. The thyroid gland is nonpalpable and non-tender. There is no proptosis or pretibial myxedema.

Laboratory studies are obtained:

TestResultReference Range
Thyroid-stimulating hormone (TSH)0.020.02 μ\muU/mL0.4−4.00.4 - 4.0 μ\muU/mL
Free thyroxine (T4)2.82.8 ng/dL0.9−1.70.9 - 1.7 ng/dL
Serum thyroglobulinUndetectable3−403 - 40 ng/mL

A 24-hour radioactive iodine uptake (RAIU) scan demonstrates a 1%1\% uptake (reference range: 10%−30%10\% - 30\%).

Which of the following is the most likely diagnosis?

  1. Exogenous thyroid hormone ingestionCevap
  2. B
    Graves disease
  3. C
    Subacute granulomatous thyroiditis
  4. D
    Painless (silent) thyroiditis
  5. E
    Struma ovarii

Cevap

Exogenous thyroid hormone ingestion
The patient presents with symptomatic thyrotoxicosis, confirmed by a suppressed TSH and elevated free T4. The initial step in formulating a differential diagnosis for thyrotoxicosis without obvious goiter or classic physical exam findings (such as exophthalmos) is a radioactive iodine uptake (RAIU) scan. A low RAIU (typically <5%<5\%) indicates that the thyroid gland is not actively synthesizing new hormone, ruling out conditions like Graves disease or toxic multinodular goiter. The differential for thyrotoxicosis with a low RAIU includes thyroiditis (release of preformed hormone), ectopic production, and exogenous thyroid hormone ingestion. Serum thyroglobulin, a glycoprotein produced only by endogenous thyroid tissue, serves as the final distinguishing marker. It is elevated during active synthesis or follicular destruction but is suppressed when exogenous hormone causes negative feedback on the hypothalamic-pituitary-thyroid axis. The undetectable thyroglobulin confirms the diagnosis of exogenous thyroid hormone ingestion (factitious thyrotoxicosis), which is likely hidden in the patient's 'energy booster' supplement.

Adım Adım Çözüm

1
Evaluate the initial thyroid function tests.
The patient has a low TSH and high Free T4.
This confirms the presence of primary thyrotoxicosis and prompts further evaluation to determine the underlying etiology.
2
Interpret the radioactive iodine uptake (RAIU) scan.
The uptake is diffusely decreased at 1%.
A low RAIU differentiates thyrotoxicosis caused by active hormone overproduction (which would have high uptake) from preformed hormone release, ectopic production, or exogenous intake.
3
Assess the serum thyroglobulin level in the context of a low RAIU.
The thyroglobulin is undetectable.
Thyroglobulin distinguishes between endogenous thyroid tissue destruction/ectopic production (high thyroglobulin) and exogenous thyroid hormone administration (low/undetectable thyroglobulin).

Anahtar Kavram

Differentiating etiologies of thyrotoxicosis using radioactive iodine uptake and serum thyroglobulin levels.
Bu soruyu puanla

Konular

Formulating a Differential Diagnosis

Bu konudan daha fazla soru