Hypothyroidism

Question 1

Etiologies of hypothyroidism

Answer 1

• Chronic lymphocytic (hashimotos) thyroiditis
• Idiopathic/atrophic thyroiditis
• Iatrogenic (thyroidectomy, I131 Rx, radiation, drugs: Li, iodine, PTU, tapazole, TKIs, amiodorone)
• Pituitary/hypothalamic disease
• Cretinism

Question 2

Physiologic response to hypothyroidism

Answer 2

• Reduced heat production due to decreased metabolic rate (feel cold)
• Decrease in beta adrenergic responsiveness (decreased receptor number and sensitivity, increased phosphodiesterase activity)
• Unaltered alpha adrenergic response, leading to vasoconstriction and reduced heart rate

Question 3

Signs and Sx of hypothyroidism

Answer 3

• Aches and pains, fatigue, depression, trouble concentrating, modest weight gain, constipation, cold intolerance, increased sleeping, dry skin and hair, yellowish skin
• Cool/dry skin, mild HTN, delayed return of DTRs (upstroke normal, but return stroke is prolonged), bradycardia, muscle weakness
• TSH is best test since its most sensitive (TSH will be high)

Question 4

Chronic autoimmune thyroiditis (hashimotos)

Answer 4

• Autoimmune T cell destruction of the thyroid gland
• There are defective T suppressor cells, combined w/ environmental/genetic factors, leading to abnormal Ag presentation and immune invasion of thyroid gland
• Th1 response leads to cytokine and T cell destruction, along
• Early stage (adolescence): rubbery, diffuse contender goiter (like a lymph node), ASx and euthyroid
• Late stage (adults): atrophic fibrotic gland, signs and Sx of hypothyroidism, low T4 and markedly elevated TSH, positive anti-TPO
• T3 will usually be normal, since all of the T4 is being converted to T3 for maximum activity
• Progression: first there is positive TPO, then TSH rises, then FT4 falls (after TSH falls there’s a 5% chance/yr of hypothyroidism to develop)

Question 5

Rx of hypothyroidism

Answer 5

• Life-long thyroid hormone replace (LT4), follow FT4 levels for first 8 wks then TSH after 12 wks (TSH lag phase)
• Cannot take LT4 w/ Ca, Fe, PPI (H+ pump inh) b/c these reduce the absorption of LT4
• High risk pts are elderly (want to start them off slowly), b/c don’t want to provoke angina by increasing O2 demand when they don’t have the ability to supply the O2
• Must increase LT4 to upper 1/3rd nl range in women who are pregnant (and hypothyroid) during 1st trimester, and maintain that level for the entire pregnancy

Question 6

Fetal thyroid ontogenesis

Answer 6

• Maternal thyroid hormone supplies fetus for first 1/2 of pregnancy, at which point the fetal thyroid supplies the fetus
• Untreated congenital hypothyroidism (cretinism) leads to severe mental and growth retardation

Question 7

Hypothyroidism in the elderly

Answer 7

• Do not present w/ classic Sx, there is more insidious onset (getting old)
• Minor Sx: dry skin, confusion, puffy face, deafness, loss of memory, cold intolerance
• Depression
• HTN, dyslipidemia (LDL elevation)