Endocrine Weight Loss Thyroid Function and Weight Loss 2 — Questions and Answers
Question 1: Which finding would be expected in a patient with primary hyperthyroidism causing unintentional weight loss?
- Elevated TSH, low free T4
- Low TSH, elevated free T4 (Correct answer)
- Normal TSH, elevated free T3 only
- Elevated TSH, elevated free T4
Correct answer: Low TSH, elevated free T4
Primary hyperthyroidism (e.g., Graves' disease) is characterized by excess thyroid hormone production, which suppresses TSH via negative feedback, resulting in low TSH and high free T4.
Question 2: Graves' disease causes hyperthyroidism through which unique mechanism?
- Destructive thyroiditis releasing stored T4 into circulation
- TSH receptor-stimulating antibodies (TRAb) that mimic TSH action (Correct answer)
- Autonomous thyroid nodule overproducing thyroid hormone
- Pituitary adenoma secreting excess TSH
Correct answer: TSH receptor-stimulating antibodies (TRAb) that mimic TSH action
In Graves' disease, thyroid-stimulating immunoglobulins (a subtype of TRAb) bind and chronically activate TSH receptors, driving unregulated thyroid hormone synthesis and secretion.
Question 3: A euthyroid obese patient requests thyroid hormone supplementation to boost weight loss. The evidence-based response is:
- T3 supplementation is appropriate as it raises metabolic rate more than T4
- Thyroid hormone supplementation is not indicated and risks thyrotoxicosis, bone loss, and arrhythmia (Correct answer)
- Combination T3/T4 therapy is standard practice for weight loss without thyroid disease
- TSH suppression to 0.1 mIU/L is an accepted obesity treatment strategy
Correct answer: Thyroid hormone supplementation is not indicated and risks thyrotoxicosis, bone loss, and arrhythmia
Thyroid hormone misuse for weight loss in euthyroid individuals is not evidence-based and carries significant risks including iatrogenic thyrotoxicosis, atrial fibrillation, and accelerated bone loss.
Question 4: Which condition can cause low TSH and low free T4, mimicking central hypothyroidism, in a hospitalized or critically ill patient?
- Graves' disease
- Non-thyroidal illness syndrome (sick euthyroid syndrome) (Correct answer)
- Primary hypothyroidism
- Subacute thyroiditis
Correct answer: Non-thyroidal illness syndrome (sick euthyroid syndrome)
Non-thyroidal illness syndrome occurs during acute illness; reduced T4-to-T3 conversion and suppressed hypothalamic TRH lead to low TSH and low thyroid hormone levels despite structurally normal thyroid glands.
Question 5: Which dietary mineral deficiency most directly impairs thyroid hormone synthesis?
- Magnesium
- Zinc
- Iodine (Correct answer)
- Selenium
Correct answer: Iodine
Iodine is an essential substrate for thyroid hormone synthesis; deficiency leads to goiter and hypothyroidism because T3 and T4 both require iodine atoms.
Question 6: Radioactive iodine (RAI) therapy for Graves' disease often results in post-treatment weight gain because:
- RAI directly damages the hypothalamus, increasing appetite
- Destruction of thyroid tissue causes iatrogenic hypothyroidism requiring hormone replacement (Correct answer)
- RAI stimulates insulin resistance in adipose tissue
- RAI raises cortisol levels that promote visceral fat accumulation
Correct answer: Destruction of thyroid tissue causes iatrogenic hypothyroidism requiring hormone replacement
RAI ablates thyroid tissue, commonly resulting in permanent hypothyroidism; until adequately replaced with levothyroxine, the ensuing hypothyroid state promotes weight gain.
Endocrine Weight Loss Thyroid Function and Weight Loss 2
Which finding would be expected in a patient with primary hyperthyroidism causing unintentional weight loss?