Chapter 49: Thyroid Disorders Flashcards
TH
Profound effect on:
Metabolism
Stimulates energy use
Cardiac function
Cardiac stimulation
Growth
Promotes maturation in infancy and childhood
Development
Thyroid
Produces two active hormones whose synthesis is stimulated by low plasma levels of iodine
Triiodothyronine (T3)
Synthetic T3: Liothyronine
Thyroxine (T4, tetraiodothyronine)
Synthetic T4: Levothyroxine
Thyroid function test
Serum thyroid-stimulating hormone (TSH)
Screening and diagnosis of hypothyroidism
Elevated TSH is an indicator of hypothyroidism (inverse relationship)
Serum T4 test
Can measure total T4 or free T4
Serum T3 test
Can measure total T3 or free T3
Hypothyroidism
Severe deficiency of thyroid hormone
Myxedema (adults)
Replacement therapy with thyroid hormones; in almost all cases, treatment must continue lifelong
Hypothyroidism during pregnancy
To help ensure healthy fetal development, maternal hypothyroidism must be diagnosed and treated very early
Cretinism (infancy)
Replacement therapy with thyroid hormones
Hypothyroidism in adults -clinical presentation
Pale, puffy face
Cold, dry skin
Brittle hair or loss of hair
Lowered heart rate and temperature
Lethargy and fatigue
Intolerance to cold
Impaired mentality
Hypothyroidism in adults: causes
Usually due to malfunction of the thyroid
Hashimoto disease: Chronic autoimmune thyroiditis
Insufficient iodine in the diet
Surgical removal of thyroid and destruction of thyroid with radioactive iodine
Insufficient secretion of TSH and thyrotropin-releasing hormone (TRH)
Hypothyroidism in adults -tx
Therapeutic strategy
Lifelong replacement therapy
Levothyroxine (T4)
Liothyronine (T3)
Hypothyroidism: Life Span Issues
During pregnancy
In first trimester can result in permanent neuropsychologic deficits in the child
In infants
May be permanent or transient
Can cause mental retardation and derangement of growth
Two Forms of Hyperthyroidism
Graves disease
Most common form
Affects women age 20 to 40 years
Causes exophthalmos
Toxic nodular goiter (Plummer disease)
Hyperthyroidism causes
Thyroid-stimulating immunoglobulins (TSI)
Hyperthyroidism tx
Surgical removal of thyroid tissue
Destruction of thyroid tissue
Suppression of thyroid hormone synthesis
Beta blockers (e.g., propranolol) -Treat overworking heart and tremor
Nonradioactive iodine
Thyrotoxic Crisis (Thyroid Storm) cause
Patients with thyrotoxicosis who undergo significant stress (e.g., surgery, illness)
Not triggered by a rise in thyroid hormones
Cannot be identified by laboratory testing
Thyrotoxic Crisis (Thyroid Storm) s/sx
Hyperthermia (105 F or higher), severe tachycardia, restlessness, agitation, tremor, unconsciousness, coma, hypotension, heart failure
Thyrotoxic crisis tx
Methimazole
Beta blocker
Sedation, cooling, glucocorticoids, IV fluids
Levothyroxine [Synthroid]
TH prep
Synthroid admin
Should be taken in the morning at least 30 to 60 minutes before breakfast
Synthroid ADR
Tachycardia
Angina
Tremors
Can intensify effects of warfarin
Synthroid drug interactions
Drugs that reduce levothyroxine absorption
Drugs that accelerate levothyroxine metabolism
Warfarin
Catecholamines
Other thyroid prep
Liotrix [Thyrolar]
Thyroid (Armour Thyroid, others)
From desiccated animal thyroid glands
Rarely used
Methimazole
First-line drug for hyperthyroidism
Prototype of the thioamides
Does not cause the liver damage associated with propylthiouracil (PTU)
Does not destroy existing stores of thyroid hormone
May take 3 to 12 weeks for euthyroid state
More dangerous than PTU during lactation and during the first trimester of pregnancy
Methimazole ADR
Agranulocytosis
Make sure pt knows s/sx of infection and seek medical attention
Methimazole 4 uses in hyperthyroidism
Sole form of therapy for Graves disease
Adjunct to radiation therapy until the effects of radiation become manifest
Suppresses thyroid hormone synthesis in preparation for thyroid gland surgery (subtotal thyroidectomy)
Thyrotoxic crisis
Propylthiouracil (PTU)
Inhibits thyroid hormone synthesis
Second-line drug for Graves disease
Short half-life (about 90 min)
Full benefits may take 6 to 12 months
PTU therapeutic uses
Graves disease
Adjunct to radiation therapy
Preparation for thyroid gland surgery
Thyrotoxic crisis
PTU ADR
Agranulocytosis (most serious)
Hypothyroidism
Pregnancy and lactation
Can cause severe liver damage
PTU Versus Methimazole
PTU can cause severe liver injury, whereas methimazole does not
PTU has a shorter half-life than methimazole (90 min compared to 6 to 13 hr), so it requires two or three daily doses rather than one
PTU crosses the placenta less readily than does methimazole, and concentrations in breast milk are lower
PTU blocks conversion of T4 to T3 in the periphery, whereas methimazole does not
Radioactive Iodine-131 (131I)
Radioactive isotope of stable iodine
Emits gamma and beta rays
Half-life: 8 days
2 to 3 months for full effect
Radioactive iodine 131 use in Graves’ disease
destorys thyroid tissue
Pt becomes hypothyroid
Radioactive iodine 131 advantages and disadvantages
Adv: low cost, pt do not have to get thyroid sx, death is rare, no other tissue besides thyroid is harmed,
Dis: tx has delayed effect, hypothyroidism
Nonradioactive Iodine: Strong iodine solution (Lugol solution)
Used to suppress thyroid function in preparation for thyroidectomy. PO
Lugol solution ADR
Brassy taste
Burning sensation in the mouth and throat
Soreness of the teeth and gums
Frontal headache
Coryza
Salivation
Various skin eruptions
Beta blockers
Propranolol: Can suppress tachycardia and other symptoms of Graves’ disease
Benefits derive from beta-adrenergic blockade, not from reducing levels of T3 or T4
Beneficial in thyrotoxic crisis
