Module 3 - Thyroid Disorders Flashcards
What is hyperthyroidism?
Hyperthyroidism = Excessive secretion of thyroxine (T4) and triiodothyronine (T 3)
Describe the thyroid hormone pathway
TRH increases the secretion of TSH, which stimulates the synthesis and secretion of T3 and T4 by the thyroid gland. T3 and T4 inhibit the secretion of TSH, both directly and indirectly by suppressing the release of TRH. T4 is converted to T3 in the liver and many other tissues by the action of T4 monodeiodinases. Some T4 and T3 is conjugated with glucuronide and sulfate in the liver, excreted in the bile, and partially hydrolyzed in the intestine. Some T4 and T3 formed in the intestine may be reabsorbed. Drug interactions may occur at any of these sites.
What are the 4 causes of hyperthyroidism?
A. Grave’s disease – most common cause; a/w goiter and ocular changes
B. Subacute thyroiditis – no clinical manifestations of hyperthyroidism; low serum TSH, but normal serum T4, T3 and free T3 concentrations
C. Thyroid stimulating hormone (TSH) pituitary adenoma – rare; normal or high TSH despite high free T4 and T3 concentrations
D. Toxic nodular goiter or thyroid carcinoma
E. Amiodarone therapy – inhibits conversion of T4 to T3 in all patients; thus patients with amiodarone induced hyperthyroidism may also have T4 hyperthyroidism
F. Higher incidence among women 8:1 female: male ratio
What are the subjective/physical exam findings associated with hyperthyroidism?
A. Anxiety
B. Emotional Lability
C. Weakness
D. Tremor
E. Palpitations
F. Heat intolerance
G. Increased perspiration
H. Weight loss despite normal or increased appetite
I. Hyperreflexia
J. Exertional Dyspnea
K.Fine/Thin hair
L. Graves’ ophthalmopathy- noted in 20-40% of cases; exophthalmous (bulging eyes), redness and retracting eyelids, dry/gritty ocular sensations, photophobia, excessive tearing, double vision, pressure sensation behind eye; can become sight threatening with corneal ulceration or compressive optic neuropathy
How is hyperthyroidism diagnosed?
TSH is the most sensitive test and best initial test; if TSH value is normal the likelihood of primary hyperthyroidism is low; if TSH is low, then a serum free T4 and T3 are obtained.
Once a diagnosis of hyperthyroidism is established, the cause should be determined
What test can be performed to determine the cause of hyperthyroidism?
Radioactive iodine uptake tests may be performed (contraindicated in pregnancy):
- High iodine uptake is usually indicative of Grave’s disease, but will show increased uptake in iodine-deficiency states and toxic nodular goiter.
- Low iodine uptake is usually indicative of subacute thyroiditis.
What medications can be used for symptomatic relief of hyperthyroidism?
- Propanolol (Inderal) 10mg po qid
- Metoprolol (Lopressor) 25mg po q 6-8 hours.
Subacute thyroiditis is best treated with propanolol
What are some antithyroid medications for hyperthyroidism and what are their prescribed dosages?
Methimazole (Tapazole)
- Initial Dosing: 30-60mg daily divided in three doses.
- Maintenance: 5-15 mg daily
If intolerant of Methimazole, and not surgical or radioactive iodine candidates, consider:
Propylthiouracil:
- Initial Dosing: 300-600mg daily in four divided doses
- Maintenance: 100-150mg/day in three divided doses.
When is radioactive iodine used and for how long?
- It is Utilized to kill goiters
- Normally takes up to 3-4 months to kill goiter and become euthyroid
- May need to be repeated
What is a Thyroid Storm (Thyrotoxic Crisis)?
Life-threatening condition characterized by severe manifestations of hyperthyroidism
What causes a Thyroid storm (thyrotoxic crisis)?
- Precipitated by thyroid surgery, trauma, infection, acute iodine load, thyroid medication overdose
- Proper thyroidectomy patient preparation pre-operatively has decreased incidence, it rarely occurs
- Mortality rate 10-30%
What are the symptoms of a Thyroid storm (thyrotoxic crisis)?
- Exaggeration of the usual symptoms of hyperthyroidism
- Hyperpyrexia (37.8 – 41 degrees C)
- Dilated vessels/flushing
- Profuse diaphoresis (may lose up to 4L fluid/24 hours)
- Marked tachycardia (SVT)
- Mental status changes- extreme agitation, delirium, psychosis, stupor/coma)
- GI disturbances- hyperdefecation
- Hyperglycemia
How is a Thyroid Storm (Thyrotoxic Crisis) diagnosed?
- Low TSH and high free T4 and T3 concentration –typically not more profound that in uncomplicated hyperthyroidism
- Diagnosis is based upon presence of severe and life threatening symptoms in a patient with biochemical evidence of hyperthyroidism
How do you manage patients with a Thyroid Storm (Thyrotoxic Crisis)?
Basic measures: supportive care, antipyretics, avoid aspirin-containing products or NSAIDs – potentially can interfere with binding of T4 and thyroid binding globulin resulting in exacerbated hypermetabolism
Pharmacologic therapy (3 classes):
- Agents that inhibit synthesis of thyroid hormone (anti-thyroid meds)
a. Propylthiouracil
b. Methimazole - Agents that inhibit the release of thyroid hormone (iodine preparations); given after administration of anti-thyroid meds
a. Lugol’s solution - oral
b. Sodium iodine: IV, blocks effects of thyroid hormone - Agents that block the effects of thyroid hormones (beta blockers) - controls symptoms induced by increased adrenergic tone
a. Esmolol
b. Hydrocortisone taper – reduces T4 to T3 conversion and promotes vasomotor stability
How is hypothyroidism diagnosed?
- Primary hypothyroidism: characterized by elevated serum TSH and low serum T4
- Secondary hypothyroidism: characterized by low serum T 4 and TSH that is not appropriately elevated.
What are the subjective/physical exam findings associated with hypothyroidism?
A. Extreme fatigue
B. Confusion/Coma
C. Puffiness of face/eyes
D. Bradycardia
E. Hypoventilation
F. Hypothermia
G. Hypoglycemia
H. Anorexia
I. Weight gain
J. Decreased bowel sounds
K. Constipation,
L. Coarse, brittle hair
M. Thin, brittle nails
N. Cold intolerance
O. Myxedema in extremities and periorbital edema
P. Decreased DTRs
Q. Paresthesias
R. Hair loss
S. Hoarseness
T. Decreased sweating
U. Enlarged tongue
V. Ataxia
What are some diagnostic findings associated with hypothyroidism?
- Elevated TSH
- Low or low normal T4 level
- T3 is not a reliable test for hypothyroidism
- Hypoglycemia
- Hyponatremia
- Anemia
- Elevated transaminases
- Hypercholesterolemia and elevated triglyceride levels
How do you manage a patient in myxedema coma?
- O2 supplementation and mechanical ventilation for hypercapnia as warranted
- Fluid restriction and 3% normal saline for severe hyponatremia
- D50W for severe hypoglycemia
- IV thyroid replacement:
- Levothyroxine (T4)
- Liothyronine sodium (Cytomel) (T3) as alternative
- If adrenal insufficiency is suspected, hydrocortisone IV
- Slow rewarming with blankets
