08 Thyroid Disorders Quan Flashcards
What are the thyroid hormone functions?
Growth and development (long bone growth and neuronal maturation). Increase basal metabolic rate. Body temperature. Body homeostasis
What are the main steps in Thyroid Hormone Synthesis?
Hypothalamus releases thyrotropin-releasing hormone (TRH) to stimulate anterior pituitary. Pituitary releases thyroid stimulating hormone (TSH) to activate the thyroid gland. Thyroid gland produces T3/T4
For thyroid hormone regulation, what happens with Low T4/T3 levels?
Stimulates release of TRH from hypothalamus
For Thyroid Hormone Regulation, what happens with High T4/T3 levels?
Regulate negative feedback loop. Decrease production of TRH and TSH
What is Thyroxine?
T4
What is Triiodothyronine?
T3
What is the major circulating thyroid hormone?
T4, secreted by the thyroid
Which thyroid is more potent?
T3 is 4x more potent than T4
What is the half-life like for thyroid hormones?
T4 7 days. T3 1.5 days
What are the T3 concentrations like?
T3 has lower serum concentration than T4 (80% of T3 from T4 –> T3 conversion in the periphery)
What are the normal TSH concentrations?
0.5-5 milliinternational units/L
What are the TSH concentrations like in Hyperthyroidism?
Low
What are the TSH concentrations like in Hypothyroidism?
High
What are the normal Free T4 concentrations?
0.8-2.7 ng/dL
What are the Free T4 concentrations like in Hyperthyroidism?
High
What are the Free T4 concentrations like in Hypothyroidism?
Low
What are the normal Total T4 concentrations?
4.5-10.9 mcg/dL
What are the Total T4 concentrations like in Hyperthyroidism?
High
What are the Total T4 concentrations like in Hypothyroidism?
Low
What are the normal Total T3 concentrations?
60-181 ng/dL
What are the Total T3 concentrations like in Hyperthyroidism?
High or normal
What are the Total T3 concentrations like in Hypothyroidism?
Low or normal
What is the normal range for Thyroperoxidase (TPO)?
< 100 IU/mL
What are the normal Antithyroglobulin (ATgA) levels?
< 8%
What are the normal Thyroid Receptor Antibodies (TRAb) titers?
Titers Negative
What is the definition of Hyperthyroidism?
Heterogeneous group of disorders characterized by elevated levels of thyroid hormones in the blood
What is Graves Disease?
Most common cause of hyperthyroidism. Defect in the autoimmune system. Antibodies attack thyroid gland –> hypertrophy and overproduction of thyroid hormone. Antibodies also attack eye muscles and pertibial skin (causing bulging eyes)
How does Hashimoto’s differ from Graves disease?
Hashimoto’s disease is also an autoimmune disease, but causes atrophy instead of hypertrophy of the cells, causing hypothyroidism
What are some drugs that can cause Hyperthyroidism?
Amiodarone. Lithium. Iodines. Interleuin. Interferon-a
What are the lab findings like for Subclinical Hyperthyroidism?
Low TSH. Normal T3 and T4
What are the Subjective Signs of Hyperthyroidism?
Heat intolerance. Weight loss. Amenorrhea. Diarrhea. Photophobia. Palpitations. Nervousness, irritability, insomnia. Fatigue, weakness
What are the Objective Signs of Hyperthyroidism?
Goiter (bruits, thrills). Proximal muscle weakness on physical exam (d/t decrease in serum K). Tremor on physical exam. Proptosis (bulging eyes). Thinning of hair. Tachycardia. Wide pulse pressure. Palmar erythema. Pretibial myxedema
What is the preferred treatment for Hyperthyroidism?
Radioactive Iodine Therapy (I^131). For patients with cardiac disease, elderly, toxic multinodular goiter, failed thioamides, ophthalmopathy. Safe, but can lead to chronic hypothyroidism!!!
What are the contraindications for Radioactive Iodine Therapy?
Pregnancy. Breast feeding. Thyroid cancer
How can pre-treatment with thioamide help?
Decreases stored hormones. Decreases risk of worsening hyperthyroidism. Consider in elderly patients and patients with cardiac disease
When is surgery usually considered for hyperthyroidism?
Not commonly used, with exception of thyroid cancer. Reserved for patients non-responsive or intolerant to antithyroid medications. Patients with large thyroid goiters resistant to I^131. Pregnant patients
What are the complications of surgery for hyperthyroidism?
Hypoparathyroidism. Vocal cord paralysis
What are the pharmacological treatment choices for hyperthyroidism?
Thioamides. Iodide products
What are the Thioamides used for Hyperthyroidism?
Methimazole (Tapazole). Propylthiouracil (PTU)
What is the MOA of Thioamides?
Inhibits synthesis of thyroid hormones by inhibiting thyroid peroxidase-catalyzed reactions required for iodine oxidation. Inhibits the coupling of iodotyrosines. PTU inhibits peripheral conversion of T4 –> T3
How is Prophylthiouracil (PTU) dosed?
100mg PO QID. After 4-8 weeks, 50-150mg/day
How is Methimazole (Tapazole) dosed?
Initial 30-40mg PO QD. After 4-8 weeks, 5-14mg/day
What is the duration of Prophylthiouracil (PTU)?
7 hours
What is the duration of Methimazole (Tapazole)?
24 hours
What are the ADRs associated with Thioamides?
Rash, Arthalgias, Fever, Leukopenia. Serious: Agranulocytosis, Malaise, Gingivitis, Oropharyngeal infection, Granulocyte count < 250, Hepatotoxicity (PTU)
What needs to be monitored while on Thioamides?
TFTs Q6-8 weeks until euthyroid. TFTs Q6-12 months once patient is on a stable dose. TSH level may remain suppressed for the first several months after normalization of T4 and T3. CBC for first four months
What is the DOC for thyroid storm?
Prophylthiouracil (PTU)
What is the BBW associated with Prophylthiouracil (PTU)?
Hepatotoxicity
What is the onset time for Thioamides?
4-6 weeks
Which Thioamide is more potent?
Methimazole (Tapazole)
What DDI do you need to be careful about with Methimazole (Tapazole)?
May decrease the activity of Warfarin
As an adjunctive agent for hyperthyroidism, how does potassium iodide work?
Inhibits thyroid hormone synthesis. Blocks hormone release
When should you usually treat subclinical hyperthyroidism in people >65 years?
When TSH < 0.1
For people < 65 years, which comorbidities require you to treat subclinical hyperthyroidism when TSH < 0.1?
Heart disease. Osteoporosis. Hypoerthyroid symptoms. Consider menopause
What are the risk factors for Grave’s Ophthalmopathy in Hyperthyroidism?
Elderly. Male. Smoker
What is treatment like for Graves Ophthalmopathy?
Treatment is directed at normalizing thyroid function. RAI or surgery preferred since it removes the antigen source. Corticosteroids adjunctive therapy following RAI (prednisone for 3-4 months)
What is Toxic Nodular Goiter?
More common than Graves’ Disease in the elderly. Hyperthyroidism caused by multiple hyperfunctioning nodules. Different from Graves’ in that it doesn’t have autoantibodies involved or ophthalmopathy
What is the Treatment for Toxic Nodular Goiter?
Usually I^131, but surgery may be indicated if goiter is very large
What is the link between AF and Hyperthyroidism?
AF occurs in 10-20% of hyperthyroidism patients. Spontaneous recovery (must treat if no recovery in 1 year). Thromboembolism risk. Hypermetabolic state (if patient is on digoxin, increase dose. If patient is on warfarin, decrease dose)
What is the worst type of hyperthyroidism?
Thyroid Storm
What is Thyroid Storm?
Life-threatening clinical syndrome characterized by exaggerated signs and symptoms of hyperthyroidism, fever, and altered mental status. Precipitated by concurrent illness or injury, withdrawal of antithyroid medications or following I^131
What are the symptoms of Thyroid Storm?
Temperature > 103F. Tachycardia, arrhythmias, CHF, hypotension, tachypnea, dehydration, agitation, psychosis, delirium, coma, N/V/D, hepatic failure
What are the causes of Thyroid Storm?
Abrupt cessation of antithyroid hormone, acute illness, trauma, surgery, radioactive iodine therapy
What are T4 and T3 concentrations like in Hypothyroidism?
Low. T3 can be normal
What is Hypothyroidism?
Thyroid gland fails to secrete an adequate amount of thyroid hormone (most common thyroid disorder). Majority of causes of hypothyroidism are d/t primary thyroid gland failure. May also result from diminished stimulation by TSH
What is Primary Hypothyroidism?
Thyroid gland failure (thyroid can’t produce amount of hormones pituitary calls for). Hashimoto’s disease (chronic autoimmune thyroiditis). More common than secondary
What is Secondary Hypothyroidism?
Pituitary failure. Thyroid isn’t being stimulated by pituitary to produce hormones
What is Tertiary Hypothyroidism?
Hypothalamic failure
What are some drugs that can induce Hypothyroidism?
Lithium. Amiodarone. Rifampin. Sulfonylureas. Iodine
What are the Subjective symptoms of Hypothyroidism?
Weakness, fatigue, sluggishness. Cold intolerance. Weight gain, constipation. Heavy menstrual periods. Dry skin, brittle hair. Slow speech. Muscles ache
What are the Objective symptoms of Hypothyroidism?
Goiter (primary hypothyroidism). Nonpalpable thyroid gland. Bradycardia. Edema. Cool, dry skin. Delayed relaxation of deep tendon reflexes. Depression
What is the general treatment outline for Hypothyroidism?
Thyroid hormone replacement options (synthetic (T4, T3 or combination) or natural (Variable potency and concentration ratios of T4 and T3))
What is the content of Levothyroxine?
Synthetic T4
What is the content of Liothyronine?
Synthetic T3
What is the content of Liotrix (Levothyroxine + Liothyronine)?
Synthetic T4:T3 in 4:1 ratio to mimic physiologic ratio
What are the general characteristics of Levothyroxine?
Body’s own physiologic mechanism controls production of active hormone. Stable. Uniform potency. Lack of allergenic content
What is the general dosing of Levothyroxine in Adults?
1.6-1.7 mcg/kg/day
What changes to we need to make in pregnant patients on levothyroxine?
Increase dose by 20-30%
When dose adjusting Levothyroxine, how much can you adjust?
Not to exceed increments of 12.5 to 25mcg/day. Wait at least a month between each adjustment
What do you need to remember when changing PO Levothyroxine to IV?
Use 50% of oral dose
What is the time to steady state for Levothyroxine?
6-8 weeks
What needs to be monitored while on Levothyroxine?
TFTs (in particular T4, TSH)
When is Liothyronine (Cytomel) indicated?
Short-term replacement. Diagnostic agent. IV: treatment of myxedema coma
What is the main objective to using Liotrix (Thyrolar)?
Objective is to mimic natural hormone secretion (no clear therapeutic advantage)
What is a concern about using Desiccated Thyroid Hormone (Armour Thyroid)?
Variable potency. USP allowing for 15% variation in T4 and 10% variation in T3. Check labs every 4-6 weeks when changing manufacturers
What is the main kind of drug interaction with thyroid medications?
Chelation
What is the interaction between T4 and warfarin?
T4 enhances response to anticoagulant therapy
When should patients take their thyroid medications?
30 minutes before breakfast or other medications. Food can reduce absorption and fluctuate thyroid levels
How long will patients be on their thyroid medication?
Taken for life and will require laboratory blood tests every 6-12 months once you are on a stable dose
What side effects could indicate that the thyroid hormone dose is too high?
Fast HR. Diarrhea. Nervousness, tremor, insomnia. Heat intolerance, excessive sweating. Weight loss
What is Myxedema Coma?
Life-threatening state in which severe, usually long-standing hypothyroidism markedly worsens
What are the signs/symptoms of Myxedema Coma?
TSH, T4 and T3, electrolyte abnormalities. Hypothermia. Hemodynamic instability. Difficulty thinking. Lethargy to coma. Respiratory acidosis d/t decreased respiratory rate
What are the precipitating factors of Myxedema Coma?
Cold exposure, infection trauma. Anesthesia. Abrupt discontinuation of thyroid hormones after overuse of antithyroid medications
What is the treatment plan for Myxedema Coma?
Thyroid replacement (T4: IV bolus 300-600mcg, maintenance 50-100mcg T4 daily). Hydrocortisone (50mg IV Q6h). Supportive care. Eliminate precipitating factors
What is “Euthyroid Sick”?
Abnormal TFTs (low T4 and T3) commonly found in euthyroid patients with various systemic diseases (starvation, acute infections, acute psychiatric disorders, HIV disease, chronic cardiac, pulmonary, renal, hepatic and neoplastic diseases
What are the symptoms of hypothyroidism like in elderly patients?
Symptoms may not be as pronounced. Hoarseness, deafness, confusion, dementia, ataxia, DEPRESSION, dry skin, or hair loss
What can hyperthyroidism lead to in pregnancy?
Increases the rate of fetal loss. Goal is to maintain euthyroid state
Which medication is ok to use for hyperthyroidism in pregnancy?
Previously, PTU preferred because less crosses the placenta when compared with MTM. Both may be used during pregnancy
Why does hypothyroidism occur more often in pregnancy?
Pregnant women have lower TSH and FT4 d/t the increased amount of protein in the body
How do you treat hypothyroidism in pregnancy?
Treat with T4 prior to pregnancy. DOC: Levothyroxine
What should the TSH levels be during each of the trimesters of pregnancy?
1st: 0.1-2.5, 2nd: 0.2-3, 3rd: 0.3-3
What are the consequences of having hypothyroidism in pregnancy?
Increased risk of premature birth. Low birth weight. Questionable neurocognitive defects. Miscarriage. Gestational HTN
