Chapter 40: Disorders of Endocrine Function

Question 1

Thyroid Hormone Disorders

Answer 1

• Thyroid hormones, triiodothyronine (T3) and thyroxine (T4), are regulated by thyroid-stimulating hormone (TSH) secretion from the anterior pituitary
• Thyroid hormones produced in follicular cells of thyroid (Regulators of metabolism; required for normal growth and development of tissues)

Question 2

Hypothyroidism

Answer 2

• May be congenital or acquired
• Majority are primary, due to intrinsic thyroid gland dysfunction
• Congenital hypothyroidism (cretinism) typically due to thyroid dysgenesis (lack of development)
• Secondary, due to defects in TSH production (hyposecretion) usually associated with head/brain conditions
• Most common cause of acquired hypothyroidism: lymphocytic thyroiditis (Hashimoto or autoimmune thyroiditis)
• Irradiation of the thyroid gland
• Surgical removal of thyroid tissue
• Iodine deficiency (required for T3, T4 formation) (Leads to lack of T3/T4, stimulates TSH secretion) (Increased TSH causes thyroid cells to secrete large amounts of thyroglobulin, which leads to goiter)

Question 3

Hypothyroidism: Clinical manifestaitons in infants

Answer 3

• Routine screening in newborns has resulted in increased treatment for congenital hypothyroidism
• Dull appearance, thick, protuberant tongue, and thick lips
• Prolonged neonatal jaundice
• Poor muscle tone, umbilical hernia
• Bradycardia, mottled extremities
• Hoarse cry
• Mental retardation unless treated early

Question 4

Hypothyroidism: Clinical manifestations in children/adults

Answer 4

• Decreased basal metabolic rate
• Weakness, lethargy, cold intolerance, decreased appetite
• Bradycardia, narrowed pulse pressure, and mild/moderate weight gain
• Elevated serum cholesterol and triglycerides
• Enlarged thyroid, dry skin, constipation
• Depression, difficulties with concentration/memory
• Loss of eyebrow
• Menstrual irregularity

Question 5

Diagnosis of Hypothyroidism

Answer 5

• Primary: elevated TSH (sensitive indicator of thyroid hypoactivity)
• Secondary: low TSH
• Low levels of T3 and T4 may not occur until later in the disease course

Question 6

Treatment of Hypothyroidism

Answer 6

• Goal is return of euthyroid (normal) state
• Must progress slowly
• Oral levothyroxine
• Resolution of symptoms occurs over weeks

Question 7

Hypothyroidism (Myxedema)

Answer 7

• occurs in sever or prolonged hypothyroidism
• Generalized, non-pitting edema
• Decreased level of consciousness, hypotension, hypothermia, history of precipitating event (trauma, sepsis, certain drugs)
• May progress to myxedema coma, a life-threatening condition if treatment not received

Question 8

Pathogenesis of Hyperthyroidism

Answer 8

• Most common: autoantibodies bind and stimulate TSH receptors leading to diffuse toxic goiter (Graves disease)
• Associated with certain genetic markers
• Thyromegaly
• Exophthalmos (immune mediated so may not resolve with treatment)
• Widening of the palpebral fissure resulting in exposed sclera
• Lid lag, vision changes, photophobia

Question 9

Etiology of Hyperthyroidism

Answer 9

• Thyroid hyperfunction with increased synthesis and secretion of T4 and T3 (Graves disease)
• Thyroid destruction with release of preformed T4 and T3 (Hashimoto thyroiditis)
• Primary—Graves disease, autoimmune, tumor related, inflammatory (Autoimmune—related to TSH receptor antibodies)
• Secondary—stimulation of TSH receptors by TSH (hypersecretion of TSH)

Question 10

Clinical Manifestations of Hyperthyroidism

Answer 10

• Changes in behavior, insomnia, restlessness, tremor, irritability, palpitations, heat intolerance, diaphoresis, diarrhea, inability to concentrate that interferes with work performance; enlarged thyroid gland
• Increased basal metabolic rate leads to weight loss, although appetite and dietary intake increase
• Amenorrhea/scant menses

Question 11

Diagnosis of Hyperthyroidism

Answer 11

• TSH levels (TSH helpful in differentiating primary (low TSH) from secondary (high TSH) hyperthyroidism)
• Elevated serum T4 and T3 (confirm)
• 24-hour radioactive iodine uptake study can confirm diagnosis of Graves disease and exclude presence of thyroid neoplasms

Question 12

Treatment of Hyperthyroidism

Answer 12

• Beta-blockers to block acute symptoms
• Antithyroid drugs, thionamides (propylthiouracil, methimazole)
• Radioactive iodine treatment (destroys part of thyroid for Graves disease)
• Surgical removal of the thyroid gland typically reserved for tumors
• Pituitary adenoma treated surgically

Question 13

Hyperthyroidism (Thyroid Storm)

Answer 13

• Life-threatening thyrotoxicosis that occurs when excessive amounts of thyroid hormones are acutely released into circulation
• Clinical Manifestations include Elevated temperatures, tachycardia, arrhythmias, congestive heart failure, Extreme restlessness, agitation, and psychosis (Precipitating event: stress, gland manipulation)
• Treatment includes Aggressive management to achieve metabolic balance,
  Antithyroid drugs are given followed by iodine administration, Beta-blockers to alleviate cardiac symptoms,
  Antipyretic therapy, Fluid replacement, Surgical removal of tumors, Fatal if not treated