Podcast
Questions and Answers
What is the primary mechanism by which amiodarone induces thyrotoxicosis in patients?
What is the primary mechanism by which amiodarone induces thyrotoxicosis in patients?
- By reducing the secretion of thyroid-stimulating hormone
- By causing a destructive thyroiditis with leakage of thyroglobulin and thyroid hormones (correct)
- By inhibiting the metabolism of thyroid hormone
- By increasing the synthesis of thyroid hormone
Which of the following is a physical sign of thyrotoxicosis?
Which of the following is a physical sign of thyrotoxicosis?
- Coarse, brittle hair
- Warm, smooth, moist skin (correct)
- Dry, coarse skin
- Hypoactive deep tendon reflexes
What is the estimated percentage of patients who develop subclinical hypothyroidism due to amiodarone?
What is the estimated percentage of patients who develop subclinical hypothyroidism due to amiodarone?
- 2%–3% of patients
- 5% of patients
- 50% of patients
- 25% of patients (correct)
Which of the following symptoms is NOT typically associated with thyrotoxicosis?
Which of the following symptoms is NOT typically associated with thyrotoxicosis?
What is the term for the separation of the ends of the fingernails from the nail beds?
What is the term for the separation of the ends of the fingernails from the nail beds?
Which of the following is a characteristic feature of Graves' disease?
Which of the following is a characteristic feature of Graves' disease?
What is the term for the inflammation of the thyroid gland?
What is the term for the inflammation of the thyroid gland?
What is the term for the symptoms of thyrotoxicosis, including nervousness, anxiety, and heat intolerance?
What is the term for the symptoms of thyrotoxicosis, including nervousness, anxiety, and heat intolerance?
What is the estimated percentage of patients who develop overt hypothyroidism due to amiodarone?
What is the estimated percentage of patients who develop overt hypothyroidism due to amiodarone?
Which of the following is a characteristic feature of subacute thyroiditis?
Which of the following is a characteristic feature of subacute thyroiditis?
What is the primary purpose of thyroid peroxidase in thyroid hormone production?
What is the primary purpose of thyroid peroxidase in thyroid hormone production?
Which of the following is a characteristic of thyrotoxicosis factitia?
Which of the following is a characteristic of thyrotoxicosis factitia?
What is the main difference between painful subacute thyroiditis and painless thyroiditis?
What is the main difference between painful subacute thyroiditis and painless thyroiditis?
What is the role of transthyretin in thyroid hormone physiology?
What is the role of transthyretin in thyroid hormone physiology?
What is the primary site of thyroid hormone production?
What is the primary site of thyroid hormone production?
What is the term for the combination of mono-iodo-tyrosine (MIT) and diiodotyrosine (DIT) to form triiodothyronine (T3)?
What is the term for the combination of mono-iodo-tyrosine (MIT) and diiodotyrosine (DIT) to form triiodothyronine (T3)?
Which of the following is a characteristic of multinodular goiter?
Which of the following is a characteristic of multinodular goiter?
What is the term for the unbound thyroid hormone that can diffuse into cells and elicit biologic effects?
What is the term for the unbound thyroid hormone that can diffuse into cells and elicit biologic effects?
What is the primary function of thyroid binding globulin (TBG)?
What is the primary function of thyroid binding globulin (TBG)?
What is the term for the formation of thyroxine (T4) from two molecules of diiodotyrosine (DIT)?
What is the term for the formation of thyroxine (T4) from two molecules of diiodotyrosine (DIT)?
What does an increased 24 hour RAIU indicate in a patient who is not pregnant or lactating?
What does an increased 24 hour RAIU indicate in a patient who is not pregnant or lactating?
Why is a T3 level measurement necessary in toxic adenomas?
Why is a T3 level measurement necessary in toxic adenomas?
What is a characteristic of thyroid scans in multinodular goiters?
What is a characteristic of thyroid scans in multinodular goiters?
How is TSH induced hyperthyroidism diagnosed?
How is TSH induced hyperthyroidism diagnosed?
What is a characteristic of subacute thyroiditis?
What is a characteristic of subacute thyroiditis?
What is elevated in the initial phase of subacute thyroiditis?
What is elevated in the initial phase of subacute thyroiditis?
What is a characteristic of TSH secreting pituitary adenomas?
What is a characteristic of TSH secreting pituitary adenomas?
What is a diagnostic criterion for TSH induced hyperthyroidism?
What is a diagnostic criterion for TSH induced hyperthyroidism?
What is a characteristic of thyrotoxic patients with normal T4 levels?
What is a characteristic of thyrotoxic patients with normal T4 levels?
What is a diagnostic test for toxic adenomas?
What is a diagnostic test for toxic adenomas?
What is the primary indication of true hyperthyroidism in a 24-hour radioactive iodine uptake (RAIU) test?
What is the primary indication of true hyperthyroidism in a 24-hour radioactive iodine uptake (RAIU) test?
A patient presents with thyrotoxic symptoms, but exophthalmos is absent. Which type of thyroiditis is most likely?
A patient presents with thyrotoxic symptoms, but exophthalmos is absent. Which type of thyroiditis is most likely?
What is the primary cause of thyroid storm in a patient with thyrotoxicosis?
What is the primary cause of thyroid storm in a patient with thyrotoxicosis?
What is the effect of elevated thyroid hormone levels on TSH levels in patients with thyrotoxic Graves' disease?
What is the effect of elevated thyroid hormone levels on TSH levels in patients with thyrotoxic Graves' disease?
What is the characteristic finding in the thyroid gland on physical examination in patients with painful subacute thyroiditis?
What is the characteristic finding in the thyroid gland on physical examination in patients with painful subacute thyroiditis?
What is the primary diagnostic tool for confirming thyrotoxicosis in patients with symptomatic disease?
What is the primary diagnostic tool for confirming thyrotoxicosis in patients with symptomatic disease?
What is the characteristic laboratory finding in patients with thyrotoxic Graves' disease?
What is the characteristic laboratory finding in patients with thyrotoxic Graves' disease?
What is the primary difference between painful subacute thyroiditis and painless thyroiditis?
What is the primary difference between painful subacute thyroiditis and painless thyroiditis?
What is the primary laboratory finding in patients with thyroid storm?
What is the primary laboratory finding in patients with thyroid storm?
What is the primary treatment goal for patients with thyroid storm?
What is the primary treatment goal for patients with thyroid storm?
Study Notes
Thyrotoxicosis
- Can occur when thyroid hormone is used inappropriately, in excessive doses, or accidentally ingested
- Amiodarone can induce thyrotoxicosis (2%-3% of patients), overt hypothyroidism (5% of patients), subclinical hypothyroidism (25% of patients), or euthyroid hyperthyroxinemia
- Amiodarone's high iodine content (37% by weight) can exacerbate thyroid dysfunction in patients with preexisting thyroid disease
- Symptoms of thyrotoxicosis include nervousness, anxiety, palpitations, emotional lability, easy fatigability, heat intolerance, weight loss, increased appetite, and scanty or irregular menses in women
- Physical signs include warm, smooth, moist skin, fine hair, onycholysis, lid lag, tachycardia, widened pulse pressure, and systolic ejection murmur
Thyroid Hormone Physiology
- Thyroxine (T4) and triiodothyronine (T3) are formed within thyroglobulin, a large glycoprotein synthesized in the thyroid cell
- Inorganic iodide is oxidized by thyroid peroxidase and covalently bound to tyrosine residues of thyroglobulin
- Iodinated tyrosine residues combine to form iodothyronines, which are then released into the bloodstream
- T4 and T3 are transported by thyroid binding globulin (TBG), transthyretin, and albumin
- Only unbound (free) thyroid hormone can diffuse into cells, elicit biologic effects, and regulate thyroid stimulating hormone (TSH) secretion from the pituitary
Thyroid Disorders
- Multinodular goiter: follicles with autonomous function coexist with normal or nonfunctioning follicles, leading to thyrotoxicosis
- Painful subacute thyroiditis: often develops after a viral syndrome, characterized by thyroid pain and tenderness
- Painless thyroiditis: a common cause of thyrotoxicosis, etiology not fully understood, may be caused by autoimmunity
- Thyrotoxicosis factitia: hyperthyroidism due to ingestion of exogenous thyroid hormone
- Thyroid storm: a life-threatening medical emergency characterized by decompensated thyrotoxicosis, high fever, tachycardia, and dehydration
Diagnosis
- Elevated 24-hour radioactive iodine uptake (RAIU) indicates true hyperthyroidism
- Low RAIU indicates that excess thyroid hormone is not a consequence of thyroid gland hyperfunction
- In thyrotoxic Graves' disease, there is an increase in the overall hormone production rate with a disproportionate increase in T3 relative to T4
- Measurement of serum free T4, total T4, total T3, and TSH can confirm the diagnosis of thyrotoxicosis
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