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

Diagnosis