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For further information, see CMDT Part 26-08: Hypothyroidism & Myxedema

Key Features

Essentials of Diagnosis

  • 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

General Considerations

  • 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

    • Thyroid surgery, irradiation, or radioiodine treatment

    • Deficient pituitary TSH

    • Severe illness

  • 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

Clinical Findings

Symptoms and Signs

  • Common manifestations

    • Weight gain, fatigue, lethargy, depression

    • Weakness, dyspnea on exertion

    • Arthralgias or myalgias, muscle cramps, paresthesias

    • Cold intolerance

    • Constipation

    • Dry skin

    • Headache

    • Carpal tunnel syndrome

    • Menorrhagia

    • Bradycardia; diastolic hypertension

    • Thin, brittle nails

    • Thinning of hair

    • Peripheral edema, puffy face and eyelids

    • Skin pallor or yellowing (carotenemia)

    • Delayed relaxation of deep tendon reflexes may be present

    • Palpably enlarged thyroid (goiter) that arises due to elevated serum TSH levels or the underlying thyroid pathology

  • Less common manifestations

    • Diminished appetite and weight loss

    • Hoarseness

    • Decreased sense of taste and smell and diminished auditory acuity

    • Dysphagia or neck discomfort

    • Menorrhagia, scant menses, or amenorrhea

    • Thinning of the outer halves of the eyebrows

    • Thickening of the tongue

    • Hard pitting edema

    • Effusions into the pleural and peritoneal cavities as well as into joints

    • Galactorrhea may also be present

    • Cardiac enlargement ("myxedema heart") and pericardial effusions may occur

    • Psychosis ("myxedema madness") may occur

Differential Diagnosis

  • Conditions and drugs that cause a low serum T4 or T3 or high serum TSH in the absence of hypothyroidism


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