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Essentials of Diagnosis
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Autoimmune (Hashimoto) thyroiditis is the most common cause of hypothyroidism
Weakness, cold intolerance, constipation, depression, menorrhagia, hoarseness
Dry skin, bradycardia, delayed return of deep tendon reflexes
Free tetraiodothyronine (FT4) low
Thyroid-stimulating hormone (TSH) elevated in primary hypothyroidism
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General Considerations
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Primary hypothyroidism is due to thyroid gland disease
Secondary hypothyroidism is due to lack of pituitary TSH
Maternal hypothyroidism during pregnancy results in cognitive impairment in child
Hypothyroidism with goiter is caused by
Hashimoto thyroiditis
Subacute (de Quervain thyroiditis) (after initial hyperthyroidism)
Riedel thyroiditis
Iodine deficiency
Genetic thyroid enzyme defects
Hepatitis C
Medications: Iodide, propylthiouracil or methimazole, sulfonamides, amiodarone, interferon-alpha, interferon-beta, interleukin-2, and lithium
Food goitrogens in iodide-deficient areas
Peripheral resistance to thyroid hormone
Infiltrating diseases
Hypothyroidism without goiter is caused by
Radiation therapy to the head-neck-chest-shoulder region can cause hypothyroidism with or without goiter or thyroid cancer many years later
TSH may be mildly elevated in some euthyroid individuals, especially elderly women (10% incidence)
Amiodarone, due to high iodine content, causes clinical hypothyroidism in 15–20%
High iodine intake from other sources may also cause hypothyroidism, especially in those with underlying lymphocytic thyroiditis
Myxedema is caused by interstitial accumulation of hydrophilic mucopolysaccharides, leading to fluid retention and lymphedema
Euthyroid sick syndrome
Functional hypothyroidism that occurs in serious nonthyroidal disease e.g. severe illness, caloric deprivation, or major surgery
Patients without known thyroid disease have a low serum FT4 and a serum TSH that is not elevated
Does not require treatment with levothyroxine
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Differential Diagnosis
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