Thyroid Disorders: Hypothyroidism

• Thyroid disorders involve both thyroid and antithyroid drugs.

Thyroid Gland

• The thryroid gland secretes three hormones essential for metabolism regulation.
• It secretes thyroxine (T4), triiodothyronine (T3), and calcitonin (which helps build T3 and T4).
• The conversion of T4 to T3 requires iodine.
• The thyroid gland lies near the parathyroid gland and is responsible for mantaining adequate calcium levels in extracellular fluid.

Hypothyroidism: Etiology and Pathophysiology

• Hypothyroidism can be primary, secondary, or tertiary.
• Primary hypothyroidism involves an issue with the thyroid gland itself.
• It is commonly related to the destruction of thyroid tissue or defective hormone synthesis.
• Hormone findings in primary hypothyroidism include decreased T3, decreased T4, and increased thyroid stimulating hormone (TSH).
• Secondary hypothyroidism is rare and related to pituitary disease (tumor) with decreased TSH secretion.
• Tertiary hypothyroidism involves a reduced level of thyrotropin releasing hormone (TRH) from the hypothalamus.

Disorders of Thyroid Gland

• The disorders of the thyroid gland can be visualized on a continuum.
• Moving from hyperthyroidism to hypothyroidism goes from thyroid storm, hyperthyroidism, euthyroid, hypothyroidism, and myxedema coma.

Transient Hypothyroidism

• Hypothyroidism may be transient
• It can be related to thyroiditis or discontinuing thyroid hormone therapy.

Congenital Hypothyroidism

• Congenital hypothyroidism involves hyposecretion of thyroid hormone during youth.
• Low metabolic rate, retarded growth, and mental development.

Myxedema

• Myxedema is caused by hyposecretion of thyroid hormone during adulthood.
• It results in a decreased metabolic rate, loss of mental and physical stamina, weight gain, loss of hair, firm edema, and yellow dullness of the skin.

Goiter

• Goiter is caused by the enlargement of the thyroid gland.
• It results from overstimulation by elevated levels of TSH.
• TSH is elevated because there is little to no thyroid hormone in circulation.

Normal Negative Feedback

• Normal negative feedback starts with the hypothalamus releasing TRH.
• Then the pituitary releases TSH.
• Then the thyroid gland releases T3 and T4.
• T3 and T4 are sensed by the hypothalamus and/or pituitary.
• When the T3 and T4 levels are adequate, TRH and TSH turns off.

Goiter Process

• Goiter process starts with the hypothalamus releasing TRH.
• The pituitary releases TSH.
• The thyroid gland does not produce T4 and T3.
• There is no message to stop TRH and TSH.
• Overstimulation results from elevated TSH levels.
• TSH is elevated because there is little or no thyroid hormone in circulation.

Hypothyroidism

• Iodine deficiency causes hypothyroidism because iodine converts T4 to T3.
• It is the most common cause worldwide and prevalent in iodine-deficient areas.
• Atrophy of the gland is the primary cause where iodine intake is adequate.
• Hypothyroidism can also develop because of treatment for hyperthyroidism (Graves Disease).
• Amiodarone and lithium can cause hypothyroidism.
• Treatments essentially kill the gland to stop thyroid hormone overproduction, thus patients need lifelong thyroid replacement prescriptions.

Hypothyroidism: Clinical Manifestations

• Clinical manifestations vary depending on severity and duration.
• Systemic effects are characterized by a slowing of body processes.
• Clinical manifestations range from no symptoms to easily detected physical changes.
• Onset of symptoms occurs over months to years.
• Unless the onset occurs after thyroidectomy, thyroid ablation or treatment with antithyroid drugs.

Myxedema Coma

• Myxedema coma involves mental sluggishness and drowsiness.
• It results in lethargy progressing gradually or suddenly to impairment of consciousness or coma.
• Infection, exposure to cold, trauma, and certain drugs can be precipitants.
• Myxedema coma is characterized by subnormal temperature, hypotension, and hypoventilation.
• The vital functions must be supported and the patient must be administered an IV hormone replacement to survive.

Thyroid Replacement Drug Therapy

• Thyroid hormones are a form of thyroxine (T4), liothyronine (T3), or a combination of T3 and T4.
• Thyroid preparations increase metabolic rate, protein synthesis, cardiac output, renal perfusion, oxygen use, body temperature, blood volume and growth process.
• Thyroid preparations replace what the thyroid gland cannot produce to achieve normal thyroid levels.
• Levothyroxine (Synthroid, Levothyroid, Levoxyl) is a synthetic thyroid hormone T4.
• Liothyronine (Cytomel) is a synthetic thyroid hormone T3.
• Liotrix (Thyrolar) is a synthetic thyroid hormone T3 and T4 combined.
• Oral medications should be taken ½ hour to 1 hour before breakfast to facilitate absorption.

Indications for Thyroid Replacement Drug Therapy

• Thyroid replacement drugs treat all three forms of hypothyroidism
• Levothyroxine is the preferred drug for its predictable hormonal content and effect.
• Thyroid medications are used for thyroid replacement in patients who've had the thyroid glands surgically removed or destroyed.
• It can also be used for emergency treatment of myxedema coma and hypothyroidism in pregnancy.

Adverse Effects of Thyroid Drug Therapy

• Cardiac dysrhythmia, most significant adverse effect of thyroid meds.
• Other adverse effects include tachycardia, palpitations, angina, hypertension, insomina, tremors, and headache.
• Also see heat intolerance, sweating, appetite changes, weight loss from increased metabolism, menstrual irregularities, diarrhea, nausea, and anxiety.
• All medications can result in hyperthyroidism.

Thyroid Replacements Drug Therapy: Contraindications

• Thyroid replacement drugs are not used to treat obesity.
• Because of cardiac stimulation, thyroid replacement drugs are contraindicated following an MI.

Thyroid Replacements Drug Therapy: Interactions

• Binding agents, cholestyramine, antacids, antiseizure medications, and anticoagulants can cause interactions.

Nursing Implications

• Assess for drug allergies, contraindications, potential drug interactions and obtain baseline vital signs as well as weight.
• Use with caution for those with cardiac disease, hypertension, and pregnant women.
• During pregnancy, treatment for hypothyroidism should continue for the well-being of the fetus.
• Fetal growth may be retarded if maternal hypothyroidism is untreated.
• Adjust dosage every 4 weeks to keep TSH at the lower end of the normal range.

Nursing Implications

• Teach patients to take thyroid drugs once daily in the morning.
• Take the medication at the same time every day.
• Not to switch brands without physician approval.
• Patients need to report unusual symptoms, chest pain, or palpitations to a physician.
• Do not take over-the-counter medications without physician approval.
• Therapeutic effects may take several months to occur.

Nursing Implications

• Teach patients the importance of alerting health care providers of thyroid medication use.
• May enhance activity of antiocoagulants (stimulation of glucose)
• Diabetic patients may need increased dosages of hypoglycemic meds.
• May decrease serum digoxin levels.

Hyperthyroidism

• Grave's disease, an autoimmune disease
• Multinodular disease
• Plummer's disease (rare, toxic nodular disease)
• Thyroid storms are all causes of hyperthyroidism.
• Thyroid storm (induced by stress or infection) and is severe and life-threatening.

Hyperthyroidism: Etiology and Pathophysiology

• Sustained increase in synthesis and release of thyroid hormones by thyroid gland.
• It occurs more often in women, in their 20-40s.
• Thyrotoxicosis is the clinical syndrome of hypermetabolism resulting from increased circulating levels of T3 and/or T4.
• Hyperthyroidism and thyrotoxicosis occur together as graves' disease.

Hyperthyroidism: Graves Disease (Etiology and Pathophysiology)

• Grave's disease is an autoimmune disease of uncertain origin.
• It causes diffuse thyroid enlargement and excessive thyroid hormone secretion (T3 and T4).
• Antibodies develop to the TSH receptor, leading to clinical manifestations of thyrotoxicosis, potentially progressing to destruction of thyroid tissue resulting in hypothyroidism.
• Precipitating factors include insufficient iodine supply, infection, and stressful events interacting with genetic factors.
• Grave's disease accounts for 75% of cases of hyperthyroidism.

Hyperthyroidism: Clinical Manifestations

• Hyperthyroidism is related to the effect of thyroid hormone excess and increased metabolism coupled with increased tissue sensitivity to stimulation by the sympathetic nervous system.
• Patients with hyperthyroidism have an intolerance to heat, increased sensitivity to stimulant drugs, as well as an elevated basal temperature.

Hyperthyroidism: Complications

• Thyrotoxic crisis is caused by excess amounts of thyroid hormones.
• It is an acute, rare condition, where all manifestations are heightened (life-threatening).
• Death is rare when treatment is initiated.
• Presumed causes are additional stressors.

Thyrotoxic Crisis: Clinical Manifestations

• Tachycardia
• Heart failure
• Shock
• Hyperthermia
• Restlessness and agitation
• Seizures
• Abdominal pain and nausea
• Vomiting and diarrhea
• Delirium and coma

Thyrotoxic Crisis: Treatment

• Treatment's goal is to decrease thyroid hormone levels and clinical manifestations with drug therapy.
• Therapy aims to reduce respiratory distress and fever, provide fluid replacement and manage stressors.

Treatment of Hyperthyroidism

• Radioactive iodine works by destroying the thyroid gland, but results in lifelong thyroid hormone replacement.
• Surgery removes all or part of the thyroid gland, resulting in lifelong thyroid hormone replacement.
• Antithyroid drugs: thioamide derivatives such as methimazole (Tapazole) or propylthiouracil (PTU).
• Betablockers are used for symptom management only by blocking sympathetic response.

Antithyroid Drugs

• Antithyroid drugs include methimazole (Tapazole) and propylthiouracil (PTU).
• Inhibit the incorporation of iodine molecules into the amino acid tyrosine.
• Tyrosine is required to make T3 and T4.
• Therapeutic uses include Grave's disease and achieving a euthyroid state prior to removal of thyroid.
• This also becomes an adunct to irradiation of the thyroid gland and emergency treatment of thyrotoxicosis.

Anti-thyroid Drugs: Concerns

• Adverse effects include red blood cells, white blood cells, bone marrow toxicity, inability to fight infection, and liver injury.
• Over medication can lead to symptoms of hypothyroidism.
• Drug allergies are the only contraindication.
• Nursing considerations are monitoring vital signs and I&O, weighing a patient.
• Instruct patients to take the medications at a consistent time each day with food, and do not discontinue abruptly.
• Monitor for indications of hypothyroidism, and monitor CBC.
• Beta-blockers may be given to decrease tremors and tachycardia.

Cost of Drugs

• Levothyroxine – 90 tablets is about $56 without insurance.
• PTU - $100 without insurance, $18 with insurance
• Methimazole – 90 tablets $20 with insurance