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¶
-
Treatment 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 with 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 with CAD: 25-50 mcg daily
-
-
Increased doses required for: 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
-
Pregnancy: 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
-
Hypothyroid pts are at increased risk for preeclampsia, placental abruption, preterm labor/delivery
-
Refer to endocrine for close monitoring and adjustment to avoid fetal complications
-
Inpatients who are pregnant and have abnormal TFTs warrant endocine consult.