Thyroid Flashcards
Thyroid stimulating hormone - stimulates the thyroid to do what?
Iodinize thyroglobulin and produce thyroxine (T4) and triiodothyronine (T3)
What does thyroid peroxidase do?
Oxidizes iodide to form iodine atoms which are then added onto thyroglobulin to produce thyroid hormones
What percentage of thyroid hormone secreted by the thyroid is T4?
80%
What percentage of thyroid hormone secreted by the thyroid is T3?
20%
What is the primary extra-thyroidal site of T3 production?
The liver
Thyroid effect on the brain?
Promote normal brain development
Thyroid effect on bones?
Promote normal growth and skeletal development
Thyroid effect on the heart?
Increases sympathetic response (increased B-receptors)
Thyroid effect on lungs?
Increased ventilation
Thyroid effect on kidneys?
Overall increase in renal function
Thyroid effect on overall metabolism?
Increased rate of carbohydrate consumption
Increased body temp
Primary hypothyroidism - describe?
90% of all cases of hypothyroidism are primary
Problem is malfunctioning thyroid
Increased TSH (Hellooooo, McFly!!)
Primary causes of hypothyroidisim - name three
- Hashimoto
- Surgery or radiation
- Iodine deficiency
What is going wrong in Hashimoto’s Disease?
Autoantibodies target thyroid peroxidase, resulting in decreased T3/T4 production
Hypothyroid disease
Secondary hypothyroidism - describe:
Hypothalamus or pituitary insufficiency (lack of TRH or TSH)
Thyroid gland itself is fine
Hypothyroidism - S/S?
Intolerance to cold Facial/eyelid edema Fatigue Anorexia Brittle nails and hair Menstrual disturbances Lethargy Dry skin Constipation Muscle aches
A neck goiter would be seen in…?
Iodine deficiency hypothyroidism
What is cretinism?
Severely stunted mental and physical retardation due to sustained congenital hypothyroidism
What is the drug of choice for treatment of primary hypothyroidism?
Levothyroxine (Synthroid)
Monitoring for thyroid replacement therapy?
Baseline TSH and FT4
Every 6 to 8 weeks until normal
Every 6 to 12 months if controlled
What type of drug is Levothyroxine?
Synthetic T4
Dessicated thyroid - problems?
Animal source
Greatest risk of hypersensitivity
Varied potency
Mad cow disease risk
Levothyroxine - note regarding older adults with cardiac disease?
They should start on a lower dose (25mcg/day)
Liothyronine - MOA?
Synthetic T3
Liothyronine - notable for..?
Good option for patients who cannot convert T4 to T3
Liotrix - MOA?
T4/T3 4:1 ratio (mimic the body’s natural balance)
Remember LioTRIX is a MIX of T4 and T3
Myxedema coma - describe:
The end state of untreated hypothyroidism
Loss of brain function
Myxedema coma - tx?
Levothyroxine
Hydrocortisone (until adrenal suppression can be rules out)
Thyrotoxicosis - describe:
Condition caused by overactive thyroid leading to too much thyroid hormone in the body
Hyperthyroidism - values for TSH and FT4?
Low TSH (pituitary saying “stop making it!”)
High FT4 (thyroid making too much)
Thyroid storm - describe:
Decompensated form of thyrotoxicosis
Can be fatal
What is the most common cause of hyperthyroidism?
Graves Disease (60-80% of cases)
Describe Graves Disease:
Autoimmune disorder
Autoantibodies that mimic TSH stimulate T4/T3 production in the thyroid
What is Plummer’s Disease?
Excessive thyroid secretion from autonomous hyperfunctioning nodules
Hyperthyroidism - S/S?
Hyperthermia Exopthalmos Facial flushing Tachycardia Hypertension Muscle wasting Tremors Diarrhea
Older patients: anorexia, confusion, constipation
What is the treatment of choice for non-pregnant patients with Graves Disease, multinodular goiter, or toxic ademona?
Radioactive iodine
What is a common unintended effect of radioactive iodine?
Patients become hypothyroid (then we can just give synthroid)
Contraindication for radioactive iodine?
Pregnancy
Treatment of choice for severe hyperthyroidism?
Partial or total thyroidectomy
Thioamide - MOA?
Inhibits thyroid perioxidase, blocking iodination of thyroid hormones
May block T4-T3 conversion in the periphery, as well
Takes several weeks to work
What is the preferred agent for pharmacologic tx of hyperthyroid?
Methimazole (Tapazole)
Methimazole - pregnancy category?
D
Propythiouracil (PTU) - use?
Tx of Hyperthyroid
Drug of choice for pregnancy, nursing, and thyroid storm
Thioamides (PTU and methimazole) - Black box warning?
Severe liver injury and acute liver failure
Thioamides - AE’s?
Jaundice Agranulocytosis Leukopenia Arthralgia (lupus-like symptoms) Rash
Which thioamide uses once daily dosing?
Methimazole
Which thioamide must be dosed three times a day?
Propylthiouracil (PTU)
Iodides - MOA?
Temporary inhibition of thyroid hormone synthesis (acute) by flooding the thyroid with iodide
Reduces thyroid gland’s vascularity and size
Iodides - clinical use?
Pre-op thyroidectomy
Toxic adenoma or toxic nodular goiter
Iodide - drug interactions?
Must discontinue anti-thyroid meds (methimazole, PTU) at least 3-4 days prior to administration of iodide
Radioactive iodine - what must you check before administration?
If the patient is pregnant
Which procedure results in a 25-yr 80% incidence of permanent hypothyroidism?
Administration of Radioactive iodine
Effects of lithium with respect to radioiodine?
Lithium may prolong the retention of radioiodine and increase its efficacy
Non-selective beta blockers - use in hyperthyroidism?
Control the sympathetic symptoms of thyroiditis or thyroid storm
What medicine has the most evidence of use in treatment of thyrotoxicosis?
Propranolol
Which medicine is given in the ICU for thyroid storm?
Esmolol (IV)
Which two beta blockers also inhibit the peripheral conversion of T4 to T3?
Propranolol and Nadolol
Metoprolol - use in hyperthyroidism?
Not as common because it is specific to B1 (non-specific beta blockers are preferred)
If B-blockers are contraindicated in your hyperthyroid patient, what could you use to control tachycardia?
Verapamil or diltiazem
What is thyrotoxicosis factitia?
Refers to any state characterized by thyroid hormone excess, including ingestion of excess thyroid hormone and THYROIDITIS
Precipitating causes of thyroid storm?
Trauma, infection, antithyroid agent withdrawal
Thyroid storm - presentation?
Tachycardia, tachypnea, N/V, dehydration, delirium
Therapeutic management of thyroid storm - how many therapies involved?
6
First step of thyroid storm treatment?
Suppress new hormone synthesis (PTU, methimazole)
Second step in thyroid storm treatment?
Block the release of thyroid hormone (iodide solution - rapidly blocks release of pre-formed thyroid hormone)
Third step in thyroid storm treatment?
Antiadrenergic therapy (symptom control)
Propranolol (most common) or Esmolol
Fourth step of thyroid storm management?
Administration of Acetaminophen
Lowers fever and stabilizes BP
Fifth step in thyroid storm management
Corticosteroid therapy
Reduces T4 to T3 conversion
Sixth step in thyroid storm management?
Bile acid sequestrants
Decrease recycling of existing thyroid hormone
