Hyperthyroidism

Basics

Description

  • Hyperthyroidism is the result of inappropriate overproduction of thyroid hormones by the thyroid gland
  • Occurs in 0.2–2.5% of the population in the US
  • Thyrotoxicosis is the result of having too much thyroid hormone in the body (not necessarily from overproduction):
    • Excessive exogenous thyroid hormone ingestion
    • Tumor
    • Hyperthyroidism
  • Excessive thyroid hormone production results in a continuum of disease:
    • Subclinical hyperthyroidism
    • Thyrotoxicosis
    • Thyroid storm (aka thyrotoxic crisis with life-threatening manifestations):
      • 1–2% of patients with hyperthyroidism
  • Regulation of thyroid hormone:
    • Thyrotropin-releasing hormone (TRH) from hypothalamus acts on the anterior pituitary
    • Thyroid-stimulating hormone (TSH) released by anterior pituitary gland and results in increased T3 and T4 from the thyroid gland:
      • Most of circulating hormone is T4, which is peripherally converted to T3
      • T3 is much more biologically active than T4 although it has a shorter half-life
  • The causes of hyperthyroidism can be broken down into 4 categories:
    • Excessive thyroid stimulation
    • Inappropriate thyroid hormone synthesis
    • Stores of hormones are released
    • Excessive sources of hormone (endogenous or exogenous)

Etiology

  • Primary hyperthyroidism (resulting in inappropriate hormone synthesis):
    • Toxic diffuse goiter (Graves disease)
    • Etiology for 60–80% of middle-age patients
    • Toxic multinodular (Plummer disease) or uninodular goiter
    • Excessive iodine intake
  • Thyroiditis (thyroid inflammation):
    • Postpartum thyroiditis
    • Radiation-induced thyroiditis
    • Subacute thyroiditis (de Quervain)
    • Amiodarone-associated thyroiditis
    • Chronic thyroiditis (Hashimoto/lymphocytic)
  • Metastatic thyroid cancer
  • Ectopic thyroid tissue (struma ovarii)
  • Pituitary adenoma
  • Drug induced:
    • Amiodarone
    • Lithium
    • α-interferon
    • Interleukin-2
    • Iodine (radiographic contrast agents)
    • Excessive thyroid hormone (factitious thyrotoxicosis)
    • Aspirin overdose

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