Hypothyroidism

Hypothyroidism – Griffin Bullock

Background

  • Elevated TSH and Low FT4 (primary hypothyroidism):
    • Hashimoto’s (autoimmune) thyroiditis, Iodine deficiency, drugs (amiodarone, dopamine antagonists), adrenal insufficiency, thyroid hormone resistance (genetic), non-thyroidal illness (recovery phase), post-surgery or ablation for hyperthyroidism
  • Elevated TSH and Normal FT4: subclinical hypothyroidism
  • Low-Normal TSH, Low FT4: central hypothyroidism, sick euthyroid

 

Presentation

  • Often non-specific and vague: Fatigue, cold intolerance, weight gain, constipation, dry skin, myalgia, edema menstrual irregularities, depression, mental dysfunction
  • Goiter, bradycardia, diastolic hypertension, delayed relaxation following reflex testing
  • Lab abnormalities: microcytic anemia, hypercholesterolemia, hyponatremia, elevated CK

 

Evaluation

  • TSH: If elevated repeat TSH and obtain T4
  • Lipid panel, CBC, BMP

 

Management

  • Required if T4, significantly TSH (>10), or symptoms with any lab abnormality
  • Titrate therapy to a normal TSH (unless central hypothyroidism, then target Free T4 levels)
  • Observation of asymptomatic pts w/ subclinical hypothyroidism (normal T4, mild TSH)
  • Treatment is with formulation of T4 (full replacement is approximately 1.6 mcg/kg/day)
  • Initial Dose:
    • Young/healthy patients: full anticipated dose
    • Older patients or patients w CAD: 25-50 mcg daily
  • Increased doses will be required in the following:
    • Pregnancy
    • Estrogen therapy
    • Weight gain​​​​​​​
    • PPI therapy
    • GI disorders absorption
    • Ferrous sulfate therapy

 

Additional Information

  • Pts should take Levothyroxine alone, 1 hr prior to eating to ensure appropriate absorption
  • Of note, missed doses can be taken along with the next dose
  • Symptoms improve in 2-3 weeks. TSH steady state requires 6 weeks
  • Dose can be titrated every 6 weeks based on TSH (standard management)
  • Can titrate dose in 4 weeks in pregnancy, or in 2-4 weeks for profoundly hypothyroid pts, with titration based on Free T4 rather than TSH
  • Pregnancy: signs and symptoms are similar. Pregnancy causes lab changes due to differing levels thyroid binding globulin. Use tables based on trimester to interpret values
    • TPO antibody testing should be conducted if abnormal as this affects risk of complications.
    • Referral to endocrine for close monitoring and adjustment to avoid fetal complications
    • Pts are at risk for preeclampsia, placental abruption, preterm labor/delivery