Hypothyroidism

Primary Hypothyroidism

49 y/o F with h/o HTN, hyperlipidemia, recurrent miscarriages presents with chronic fatigue and cold intolerance. Reports h/o autoimmune disease, ovulatory/menstrual dysfunction, and neck irradiation. Denies currently being pregnant. ROS positive for poor concentration, depression, and diffuse muscle pain. Medications include amiodarone and lithium. Hair thinning, goiter, proximal muscle weakness, lower extremity edema, dry skin, and delayed deep tendon reflexes on exam.

• TSH > 10 mIU/L with low free T4

• Start levothyroxine 1.6 mcg/kg/day PO and repeat TSH testing in 6 weeks

  • Adjust levothyroxine dose every six weeks until TSH within reference range

• Levothyroxine counseling

  • Take every morning on an empty stomach at least 30 minutes before food

  • Do not take within 4 hours of calcium, iron, and/or bile acid sequestrants (e.g. cholestyramine)

Notes

• Initial workup

  • Fatigue and cold intolerance are the most common symptoms of hypothyroidism

  • May be preceded by signs/symptoms of hyperthyroidism, i.e. Hashimoto’s thyroiditis. In these cases, autoimmune destruction of the thyroid gland leads to chronic hypothyroidism.

  • Amiodarone and lithium may cause thyroid dysfunction

  • Start with TSH testing

    • General reference range is 0.5 < TSH < 10 mIU/L

    • If TSH > 5.5 mIU/L, obtain free T4

• Treatment

  • TSH < 10 mIU/L and normal free T4 indicates subclinical hypothyroidism (see vignette/chart below)

  • Hypothyroidism treatment depends on age, symptoms, and pregnancy status

    • For patients 50 or older, start levothyroxine 25 mcg daily and increase by 25 mcg every 4 weeks until TSH reaches desired range

    • In newly pregnant patients, increase current levothyroxine from 7 to 9 tablets weekly (e.g. two tablets on Tuesday/Thursday and one tablet as usual on other days)

• TSH changes in previously stable hypothyroid patients being treated with levothyroxine:

  • Numerous medications may alter TSH, including SSRIs

  • Decreased levothyroxine absorption may occur with atrophic gastritis, chronic PPI use, and/or H. Pylori infection

Subclinical Hypothyroidism

69 y/o F with h/o autoimmune disease and neck irradiation presents with chronic fatigue and cold intolerance. Denies weight gain, constipation, arthralgias/myalgias, weakness, difficulty concentrating, depression. Vital signs WNL. Normal hair, thyroid, and skin on exam.

• TSH 6.9 mIU/L with normal free T4

• Obtain lipid panel, anti-thyroid peroxidase antibodies

• Treat as indicated per laboratory results

Notes

• Subclinical hypothyroidism = elevated TSH with normal free T4

• Treatment depends on age, symptoms, TSH, anti-TPO antibodies, and lipid panel (see below)

• Rule of 7’s: TSH 7 mIU/L or greater and

  • 70+ y/o = treat if symptomatic

  • Less than 70 y/o = treat