40 Questions
What is the primary mechanism by which amiodarone induces thyrotoxicosis in patients?
By causing a destructive thyroiditis with leakage of thyroglobulin and thyroid hormones
Which of the following is a physical sign of thyrotoxicosis?
Warm, smooth, moist skin
What is the estimated percentage of patients who develop subclinical hypothyroidism due to amiodarone?
25% of patients
Which of the following symptoms is NOT typically associated with thyrotoxicosis?
Weight gain concurrent with decreased appetite
What is the term for the separation of the ends of the fingernails from the nail beds?
Onycholysis
Which of the following is a characteristic feature of Graves' disease?
Thyrotoxicosis and diffuse thyroid enlargement
What is the term for the inflammation of the thyroid gland?
Thyroiditis
What is the term for the symptoms of thyrotoxicosis, including nervousness, anxiety, and heat intolerance?
Hyperthyroid symptom complex
What is the estimated percentage of patients who develop overt hypothyroidism due to amiodarone?
5% of patients
Which of the following is a characteristic feature of subacute thyroiditis?
Severe pain in the thyroid region
What is the primary purpose of thyroid peroxidase in thyroid hormone production?
To catalyze the coupling reaction of iodinated tyrosine residues
Which of the following is a characteristic of thyrotoxicosis factitia?
It is a form of hyperthyroidism due to ingestion of exogenous thyroid hormone
What is the main difference between painful subacute thyroiditis and painless thyroiditis?
The presence of a viral syndrome preceding thyroiditis
What is the role of transthyretin in thyroid hormone physiology?
To transport thyroid hormone in the bloodstream
What is the primary site of thyroid hormone production?
Thyroid follicular cells
What is the term for the combination of mono-iodo-tyrosine (MIT) and diiodotyrosine (DIT) to form triiodothyronine (T3)?
Coupling reaction
Which of the following is a characteristic of multinodular goiter?
Follicles with autonomous function coexist with normal or nonfunctioning follicles
What is the term for the unbound thyroid hormone that can diffuse into cells and elicit biologic effects?
Free thyroid hormone
What is the primary function of thyroid binding globulin (TBG)?
To transport thyroid hormone in the bloodstream
What is the term for the formation of thyroxine (T4) from two molecules of diiodotyrosine (DIT)?
Coupling reaction
What does an increased 24 hour RAIU indicate in a patient who is not pregnant or lactating?
Inappropriate iodine usage by the thyroid gland in thyrotoxic patients
Why is a T3 level measurement necessary in toxic adenomas?
To rule out T3 toxicosis in normal T4 levels
What is a characteristic of thyroid scans in multinodular goiters?
Patchy areas of autonomously functioning thyroid tissue
How is TSH induced hyperthyroidism diagnosed?
By peripheral hypermetabolism, diffuse thyroid gland enlargement, elevated free thyroid hormone levels, and elevated serum immunoreactive TSH concentrations
What is a characteristic of subacute thyroiditis?
A triphasic course of thyroid function tests
What is elevated in the initial phase of subacute thyroiditis?
Serum T4 levels
What is a characteristic of TSH secreting pituitary adenomas?
Lack of TSH response to TRH stimulation
What is a diagnostic criterion for TSH induced hyperthyroidism?
Peripheral hypermetabolism, diffuse thyroid gland enlargement, elevated free thyroid hormone levels, and elevated serum immunoreactive TSH concentrations
What is a characteristic of thyrotoxic patients with normal T4 levels?
Elevated T3 levels
What is a diagnostic test for toxic adenomas?
Failure of autonomous nodules to decrease iodine uptake during exogenous T3 administration
What is the primary indication of true hyperthyroidism in a 24-hour radioactive iodine uptake (RAIU) test?
RAIU > 30%
A patient presents with thyrotoxic symptoms, but exophthalmos is absent. Which type of thyroiditis is most likely?
Painless thyroiditis
What is the primary cause of thyroid storm in a patient with thyrotoxicosis?
All of the above
What is the effect of elevated thyroid hormone levels on TSH levels in patients with thyrotoxic Graves' disease?
TSH levels are undetectable
What is the characteristic finding in the thyroid gland on physical examination in patients with painful subacute thyroiditis?
The gland is firm and exquisitely tender
What is the primary diagnostic tool for confirming thyrotoxicosis in patients with symptomatic disease?
Measurement of serum free T4, total T4, total T3, and TSH
What is the characteristic laboratory finding in patients with thyrotoxic Graves' disease?
Elevated T4 and T3 with a disproportionate increase in T3
What is the primary difference between painful subacute thyroiditis and painless thyroiditis?
Thyroid gland tenderness
What is the primary laboratory finding in patients with thyroid storm?
Elevated T4 and T3
What is the primary treatment goal for patients with thyroid storm?
Management of symptoms and supportive care
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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