Part 1 Flashcards
What is T3 and its main source?
Triiodothyronine (T3); main source is peripheral deiodination
10% is derived from direct thyroidal secretion
What percentage of thyroid hormone physiological effects are due to T3 binding to receptors?
More than 90%
What is the effect of ionic/anion inhibitors on thyroid hormone production?
Decreases the active transport of iodine into the thyroid, leading to a reduction in thyroid hormone production
What condition is associated with the use of Guanethidine eye-drops?
Decreased Exophthalmos
What role do glucocorticoids play in hyperthyroid states?
Protect against adrenal insufficiency and relieve thyroid pain and tenderness
What is a contraindication for beta-blockers?
Decompensated heart failure unless caused solely by tachycardia
What is the effective dosage range of beta-blockers for adrenergic symptoms?
20 to 40 mg four times daily
What is the use of radioactive iodine (RAI) in hyperthyroidism?
Ablates thyroid tissue by emitting rays and particles
What is the agent of choice for Graves’ disease?
Sodium iodide 131 (131I)
What should be given prophylactically to patients receiving 131I?
Laxatives
What is the initial dosage of Propylthiouracil for hypothyroidism?
200-400 mg in divided dosages until euthyroid state
What are two causes of primary hypothyroidism?
- Autoimmune (Hashimoto’s disease)
- Iatrogenic (surgery or 131I)
What is the average daily adult replacement dose of Levothyroxine (L-T4)?
112 mcg given as a single dose
What are the goals of therapy for hypothyroidism?
- Restore normal thyroid hormone in tissue
- Provide symptomatic relief
- Prevent neurologic deficits in newborns and children
- Reverse biochemical abnormalities associated with hypothyroidism
What are the symptoms of hypothyroidism?
- Tiredness
- Weakness
- Sexual dysfunction
- Dry skin
- Hair loss
- Difficulty concentrating
- Muscle cramps
- Menorrhagia and infertility in women
What is the drug of choice for hyperthyroidism?
Carbimazole
Fill in the blank: The role of thioamides is based on _______ hormone synthesis.
[decrease in iodination of tyrosine residues]
What is the effect of thyroid hormones on the cardiovascular system in hyperthyroidism?
Increases heart rate and myocardial strength
What condition causes excessive levels of T4 or T3 in tissues?
Hyperthyroidism (Thyrotoxicosis)
What are common symptoms of hyperthyroidism?
- Hyperactivity
- Irritability
- Heat intolerance
- Palpitations
- Weight loss with increased appetite
What is the treatment approach for reducing thyroid hormone synthesis?
- Antithyroid drugs
- Ionic/Anion inhibitors
- Radioiodine (131I)
- Surgery
What is gynecomastia?
Enlargement of breast tissue in males
This condition can be caused by hormonal imbalances, medications, or certain health conditions.
What is exophthalmos?
Protrusion of the eyeballs
Often associated with hyperthyroidism, particularly Graves’ disease.
What does pretibial myxedema refer to?
Thickening of the skin on the shins
This condition can occur in patients with thyroid disease, especially hyperthyroidism.
What is the first approach to treating hyperthyroidism?
Reducing thyroid hormone synthesis
This can be achieved through antithyroid drugs, ionic/anion inhibitors, radioiodine, or surgery.
Name three antithyroid drugs.
- Propylthiouracil
- Carbimazole
- Methimazole (thiamazole)
These drugs help reduce the synthesis of thyroid hormones.
What is the role of propranolol in hyperthyroidism treatment?
To relieve symptoms by reducing thyroid hormone effects
Propranolol is a beta-blocker that helps manage symptoms such as rapid heartbeat.
What is the Wolf-Chaikoff effect?
Reduction in synthesis of thyroxin due to large doses of iodide
This phenomenon can temporarily inhibit thyroid hormone production.
What are the desired outcomes of hyperthyroidism therapy?
- Eliminate excess thyroid hormone
- Minimize symptoms and long-term consequences
Effective management aims to restore normal thyroid function and improve quality of life.
What factors influence individualized therapy for hyperthyroidism?
- Type and severity of hyperthyroidism
- Patient age and gender
- Existence of non-thyroidal conditions
- Response to previous therapy
Tailoring treatment to the individual patient is critical for effective management.
What does a suppressed radioactive iodine uptake (RAIU) indicate?
Inflammation or thyroiditis reflecting thyrotoxicosis
This suggests an excess of thyroid hormones due to the release of preformed stores.
What is the normal level of TSH?
Practically excludes abnormality
Abnormal elevated TSH levels signify hypothyroidism.
What is the initial recommended dose of L-T4 for cretinism therapy?
10–15 µg/kg daily
This helps rapidly normalize serum T4 concentration.
How is levothyroxine sodium used in adult hypothyroidism?
- 50 µg/day for 2 weeks
- 100 µg/day for 2 weeks
- 150 µg/day for life
This gradual increase helps achieve optimal thyroid hormone levels.
What is the strength of Liothyronine sodium compared to T4?
Stronger than T4 (4 times more potent)
It has a quicker onset but shorter duration of action.
What is the significance of T4 in thyroid hormone synthesis?
It is the most important source of T3 by peripheral tissue deiodination
T4 is converted to T3, the most active thyroid hormone.
What is the feedback mechanism regulating thyroxine release?
Involves hypothalamic-pituitary axis
TSH from the anterior pituitary regulates thyroxine release, which is influenced by TRH from the hypothalamus.
What are the three types of hormones synthesized by the thyroid gland?
- Thyroxine (T4)
- Tri-iodothyronine (T3)
- Thyrocalcitonin (Calcitonin)
Each hormone plays a distinct role in metabolism and calcium regulation.
What is the primary treatment for thyroid cancer following surgical removal?
L-T4 therapy to suppress TSH stimulation
This helps prevent the growth of differentiated thyroid cancers.
What is the prevalence of lithium-induced hypothyroidism in patients taking lithium?
Occurs in 20-30% of patients
Lithium can inhibit T3 and T4 secretion and is associated with goiter.
What is the impact of amiodarone on thyroid function?
Can induce hyperthyroidism in 3% of patients
Amiodarone has a high iodine content and may cause abnormal thyroid function tests.
What is the most sensitive test for diagnosing thyroid disorders?
Serum TSH
It is also the best test to evaluate treatment results in thyroid disorders.
