Hypothyroidism

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Background

  • 3-10x more common in females
  • Peak incidence age >60
  • Emergent manifestation of severe hypothyroid = myxedema coma

Etiology

  • Primary
    • Autoimmune (Hashimoto)
    • Thyroiditis (subacute, silent, postpartum)
      • Often preceded by hyperthyroid phase
    • Iodine deficiency
    • After ablation (surgical, radioiodine)
    • After external radiation
    • Infiltrative disease (lymphoma, sarcoid, amyloid, TB)
    • Congenital
    • Meds
    • Idiopathic
  • Secondary

Spectrum of Thyroid Disease

Thyroid physiology

Clinical Features

Differential Diagnosis

Symptomatic bradycardia

Evaluation

Work-up

  • TSH
  • Total and Free T4
  • Total and Free T3
  • Thyroid Binding Globulin (TBG)
  • Auto-antibodies (anti-TPO, anti-microsomal, anti-Tg)
  • Thyroid ultrasound
  • ECG - bradycardia, low voltage
  • VBG - hypercapnia from hypoventilation, possibly compensated if chronic

Categorization

Type Cause TSH FT4
Primary Failure of thyroid Elevated Low
Secondary Failure of pituitary Low Low
Tertiary Failure of hypothalamus

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Management

  • Depends on etiology [1][2]
  • If treatment started, initiate low dose as daily doses too high may lead to thyroid storm

Primary (Central) Hypothyroidism

  • Consider starting low dose levothyroxine at 25mcg daily
  • Close follow-up with primary care or endocrinology

Subclinical Hypothyroidism

  • TSH ≥10 mU/L
    • Start low dose levothyroxine at 25mcg daily with close outpatient follow up
    • Patients are at higher risk for atherosclerosis, myocardial infarction, and risk of progression to overt hypothyroidism
    • The American Thyroid Association (ATA), American Association of Clinical Endocrinologists (AACE) and the European Thyroid Association guidelines recommend initiating treatment[3][4]
  • TSH 7.0 to 9.9 mU/L
    • <65 years old
      • Start low dose levothyroxine at 25mcg daily with close outpatient follow up
    • >65 years old
      • Risk of over treatment vs. benefit is unclear[5]
      • If patient has signs and symptoms of hypothyroidism, consider endocrinology consult prior to initiating treatment
  • TSH between upper limit of normal to 6.9 mU/L
    • <65 years old
      • Initiate low dose levothyroxine at 25mcg daily only if patient has signs and symptoms of hypothyroidism
    • >65 years old
      • May be normal for older age, do not initiate treatment
      • Close outpatient follow-up for repeat labs

Disposition

  • Most hypothyroidism is treated as an outpatient
  • Admit and treat severe hypothyroidism or myxedema coma

See Also

References

  1. Ross D. Treatment of primary hypothyroidism in adults. In: UpToDate, UpToDate, Waltham, MA. (Accessed on September 21, 2022.)
  2. Ross D. Subclinical hypothyroidism in nonpregnant adults. In: UpToDate, UpToDate, Waltham, MA. (Accessed on September 21, 2022.)
  3. Garber JR, Cobin RH, Gharib H, et al. Clinical practice guidelines for hypothyroidism in adults: cosponsored by the American Association of Clinical Endocrinologists and the American Thyroid Association. Thyroid 2012; 22:1200.
  4. Pearce SH, Brabant G, Duntas LH, et al. 2013 ETA Guideline: Management of Subclinical Hypothyroidism. Eur Thyroid J 2013; 2:215.
  5. Mooijaart SP, Du Puy RS, Stott DJ, et al. Association Between Levothyroxine Treatment and Thyroid-Related Symptoms Among Adults Aged 80 Years and Older With Subclinical Hypothyroidism. JAMA 2019; 322:1977.