Hypothyroidism

Question 1

Signs and Symptoms

Answer 1

DEC BMR AND DEC SYMP NS

• Adrenergic - tired, apathetic, bradycardia, diastolic HTN, hyporeflexia, constipation
• Metabolic - cold intolerance, hypothermia, wt gain, hypercholesterolemia, Carpal tunnel, edema
• Misc - lose lateral brows, periorbital edema, dry skin, nail ridging, coarse or thin hair, hoarse voice, absent or heavy periods, depression, myalgias

Question 2

Diagnosis

Answer 2

• Initially notice low free T4
• Check TSH …
  • if high then suspect primary
  • if low or normal suspect secondary/tertiary (hypothalamus or pituitary problem)

Question 3

Causes of Tertiary Hypothyroidism

Answer 3

TRH/ hypothalamus problem

• Tumor, irradiation, MS plaque
• Meds - dopamine, high dose steroids
• Hypoathalamic adaptive / “euthyroid sick” - when illness, starvation or anorexia you adapt by dec TSH –> dec T3/T4 to reduce metabolism
• *Do not treat these patients w/ thyroxine b/c may worsen wt loss and metabolic insufficiency

Question 4

Causes of Secondary Hypothyroidism

Answer 4

TSH / pituitary problem

• Pituitary adenoma, primary tumor or mets, post-surgical, apoplexy, autoimmune, granuloma infiltration

Question 5

Causes of Primary Hypothyroidism

Answer 5

TH production problem

• Autoimmune - Hashimoto
• Other autoimmune - post partum thyroiditis when immune system inc again (many have underlying Hashimoto’s); can be transient or permanent
• Endemic - iodine def (esp in poor countries); iodine tablets as tx
• Iodine excess - contrast, amiodarone, too many supplements (STOP)
• Post - RAI Tx or Post-surgery (purposeful low TH)
• Meds - iodine, anti-thyroid drugs, lithium
• Radiation - for lymphoma, carcinoma of larynx or esophagus
• Infiltration
• Congenital - agenesis or lingual thyroid (lifelong replacement), enzyme defects
• Transient - recovery from thyroiditis (subacute or painless/post-partum) often start as hyperthyroid as stores released but may progress to hypothyroid
• Goitergens

Question 6

Hashimoto

Answer 6

• Lymphocytic invasion and germinal center formation in thyroid
• Damage via TSH receptor antibodies and destruction of gland by invading cells
• If active inflammation/ destruction - can have painful gland and release TH from follicles –> hyperthyroid
• Gross - fleshy and tan; any size (usually small)
• Histo - atrophic follicles and filled w/ lymphocytic infiltrate (may even form germinal centers)
  
  • More lymphocytes than follicles
  • Hurthle cell change - when thyroid cells are irritated they take on cracked egg appearance
• Later scar formation and antibodies disappear; diagnosed w/ “idiopathic hypothyroid” but likely burnt out Hashimoto’s
• Tx - thyroid replacement

Question 7

Specific Congenital Enzyme Defects

Answer 7

• TSH receptor defects
• TPO, thyroglobulin, sodium iodide symporter, pendrid or thyroid oxidase 2 mutations
• MCT8 defect
• Pendrid Syndrome - inherited deafness from cochlear defect and goiter by 20s (mild)

Question 8

Goitergens

Answer 8

• ingestion of foods w/ chemicals similar to anti-thyroid drugs (weak but can cause problems if substantial part of diet)
• Ex) cabbage, turnips, rutabagas, cassava, millet

Question 9

Thyroid Hormone Replacement Therapy

Answer 9

• Levothyroxine LT4 (assume people can convert T4 to T3); T3 has much shorter half life
• T3 is available as liothyronine or Cytomel; rarely used
• MONITOR - takes 6 wks to reach new steady state so check 6-8 wks after administration

Question 10

Who may need greater dose of thyroid hormone replacement?

Answer 10

• Pregnancy (use T4 - crosses placenta)
• Oral contraceptives (inc TBG binding)
• Dec absorption (PPIs, celiac)
• Meds that inc thyroid hormone metabolism (carbemazepine, phenytoin, barbiturates)
• Nephrotic syndrome

Question 11

Myxedema

Answer 11

emergency

• Hypothermia, hypoventilation, bradycardia, pleural/pericardial effusions, cardiac failure, ileus, altered mental status, seizures or coma
• May have absent or delayed deep tendon reflexes
• Often in elderly w/ untreated or under-treated hypothyroid and precipitating event (illness, cold, surgery, meds w/ CNS depression)
• Tx - start immediately if high clinical suspicion while wait for TSH and free T4
  - LT4 alone, LT3 then LT4 or combo of LT3 and LT4
  - Give initial IV bolus then daily dose