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Updated: Jun 1 2021

Hashimoto Thyroiditis
  • A 38-year-old woman presents to her primary care physician with complaints of increased fatigue. On further review, she also reports that she has been experiencing a 15-pound weight gain, cold intolerance, and constipation over the past few months. On physical exam, she is bradycardic, has a puffy face with periorbital edema, has thinning hair, exhibits delayed relaxation of deep tendon reflexes, and is without a goiter.
  • Clinical definition
    • primary hypothyroidism due to the autoimmune destruction of the thyroid gland
  • Epidemiology
    • most common cause of primary hypothyroidism
    • predominantly female (10-15 x higher)
    • 30-50 years of age
  • Risk factors
    • family history
    • autoimmune disease
  • Pathogenesis
    • anti-thyroid antibodies destroy thyroid cells leading to insufficient production of thyroid hormone
      • anti-thyroid peroxidase 
      • anti-thyroglobulin
    • damaged thyroid cells can initially leak stored thyroid hormone into circulation leading to transient hyperthyroidism before the onset of hypothyroidism
  • Associated conditions
    • pernicious anemia
    • celiac disease
    • type 1 diabetes
  • Prognosis
    • excellent with treatment
    • myxedema coma has a high mortality rate
  • Symptoms 
    • weakness and fatigue
    • cold intolerance
    • constipation and ileus
    • weight gain
    • depression, slow mentation, and inability to concentrate
    • heavy menstruation
    • galactorrhea  
      • thyrotropin-releasing hormone can stimulate prolactin secretion
    • hoarseness
    • myopathy
    • dementia/memory loss  
  • Physical exam
    • dry and cold skin
    • puffy face with periorbital edema
    • non-pitting edema (myxedema due to glycosaminoglycan in the interstitium)
    • thinning hair and nails
    • bradycardia
    • delayed relaxation of the deep tendon reflexes
    • thyroid gland can be atrophic, normal, or enlarged
  • Special presentation
    • subclinical 
      • elevated thyroid stimulating hormone (TSH) but normal thyroid hormones
      • does not require treatment unless auto-antibody positive or symptomatic
  • Diagnostic testing
    • diagnostic approach
      • screen and confirm with lab tests
    • studies
      • TSH and free T4
        • primary screening
        • TSH is the most sensitive measure
        • lab results may be confounded by high doses of biotin supplementation
      • autoantibody
        • diagnose Hashimoto versus other etiologies of hypothyroidism
        • anti-thyroid peroxidase (90% of cases)
        • anti-thyroglobulin (50% of cases)
        • 10-15% are antibody negative
    • imaging
      • not routinely indicated
    • biopsy
      • fine needle aspiration for any dominant nodule or fast-growing goiter
      • histopathology is the gold standard for diagnosis but invasive
        • diffuse lymphocytic and plasma cell infiltration is characteristic of Hashimoto thyroiditis 
  • Diagnostic criteria
    • ↑ TSH and ↓ free T4
      • in early disease, TSH and free T4 may be normal
    • positive antithyroid autoantibodies
  • Euthyroid sick syndrome
    • distinguishing factors
      • ↓ thyroid hormone but also ↓TSH
      • secondary to nonthyroidal systemic illness
  • Thyroid lymphoma
    • distinguishing factors
      • rapidly enlarging goiter
      • lymphoma on histopathology
  • Panhypopituitarism
    • distinguishing factor
      • loss of pituitary hormones in addition to ↓ T4 including ↓ cortisol, ↓ sex steroids, ↓ growth hormone, and ↓ antidiuretic hormone
  • Major depressive disorder
    • distinguishing factor
      • lack of cold intolerance, integumentary changes, myxedema, and goiter
  • Management approach
    • thyroid hormone replacement to achieve a euthyroid state within 2-4 weeks
    • monitor clinically and with TSH
    • monitor for other associated complications
      • mild anemia
      • ↑ total cholesterol, low-density lipoprotein, and triglycerides
      • ↓ high-density lipoprotein
      • hyponatremia
  • First-line
    • lifelong levothyroxine replacement
      • requires adjustment during pregnancy 
      • adverse effects include overreplacement leading to osteoporosis and arrhythmias
      • administer empirically without lab confirmation in myxedema coma 
  • Second line
    • surgery
      • indicated for obstructive symptoms (dysphagia, stridor, and hoarseness), malignancy, and cosmesis 
  • Thyroid lymphoma or other thyroid malignancy 
  • Iatrogenic overreplacement
  • Myxedema coma
    • life threatening complication of hypothyroidism
    • start empiric treatment with IV levothyroxine if high suspicion
    • can support diagnosis with TSH and free T4 level 
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