Goiter, Endemic

Essentials of Diagnosis

• Common in regions with low-iodine diets

• High rate of congenital hypothyroidism and cretinism

• Goiters may become multinodular and enlarge

• Most adults with endemic goiter are euthyroid; however, some are hypothyroid or hyperthyroid

General Considerations

• Cretinism occurs in up to 0.5% of iodine-deficient populations; less severe manifestations of congenital hypothyroidism more common

• Causes

  • Iodine deficiency (most common)

  • Certain foods (eg, sorghum, millet, maize, cassava)

  • Mineral deficiencies (selenium, iron, zinc)

  • Water pollutants

  • Congenital partial defects in thyroid enzyme activity

Symptoms and Signs

• Thyroid may become multinodular and very large

• Growth often occurs during pregnancy, increasing the size of thyroid nodules and causing new nodules; compressive symptoms may occur

• Substernal goiters usually asymptomatic but can cause

  • Tracheal compression

  • Respiratory distress

  • Dysphagia

  • Superior vena cava syndrome

  • Phrenic or recurrent laryngeal nerve palsy, or Horner syndrome

  • Gastrointestinal bleeding from esophageal varices

  • Pleural or pericardial effusions (rare)

• Cerebral ischemia and stroke can result from arterial compression or thyrocervical steal syndrome

• Malignancy in < 1%

• Some patients with goiter become hypothyroid

• Other patients become thyrotoxic as goiter grows and becomes more autonomous, especially if iodine added to diet

• Congenital hypothyroidism

  • Isolated deafness

  • Short stature

  • Impaired mentation

Differential Diagnosis

• Benign multinodular goiter

• Pregnancy (in areas of iodine deficiency)

• Graves disease

• Hashimoto thyroiditis

• Subacute (de Quervain) thyroiditis

• Drugs causing hypothyroidism

  • Lithium

  • Amiodarone

  • Propylthiouracil

  • Methimazole

  • Phenylbutazone

  • Sulfonamides

  • Interferon-alpha

  • Iodide

• Infiltrating disease, eg, malignancy, sarcoidosis

• Suppurative thyroiditis

• Riedel thyroiditis

Laboratory Tests

• Serum thyroxine and thyroid-stimulating hormone (TSH) usually normal

  • TSH low if multinodular goiter becomes autonomous in presence of sufficient iodine for thyroid hormone synthesis, causing hyperthyroidism

  • TSH high in hypothyroidism

• Serum levels of antithyroid antibodies usually undetectable or low

• Serum thyroglobulin often elevated above 13 mcg/L

Imaging Studies

• Thyroid radioactive iodine uptake usually elevated, but may be normal if iodine intake has improved

Medications

• Dietary iodine supplementation (eg, addition of potassium iodide to table salt)

  • Greatly reduces prevalence of endemic goiter and cretinism but is less effective in shrinking established goiter

  • Has not proven effective for treating adults with large multinodular goiter and actually increases their risk of developing thyrotoxicosis

Surgery

• Thyroidectomy indicated for cosmesis, compressive symptoms, or thyrotoxicosis in adults with very large multinodular goiters

Procedures

• Patients may be treated with ¹³¹I for large compressive goiters

Follow-Up

• Partial thyroidectomy is followed by a high goiter recurrence rate in iodine-deficient geographic areas, so total thyroidectomy is preferred when surgery is indicated

Complications

• Dietary iodine supplementation increases the risk of autoimmune thyroid dysfunction, which may cause hypothyroidism or hyperthyroidism

• Excessive iodine supplementation increases the risk of goiter

• Levothyroxine supplementation

  • May induce hyperthyroidism in individuals with autonomous multinodular goiters

  • Therefore, levothyroxine suppression should not be started in patients with suppressed TSH levels

• Rarely, Graves disease can develop 3–10 months after ¹³¹I treatment in patients with large multinodular goiters

Prevention

• Iodized salt contains iodine at about 20 mg per kg salt

• Other sources of iodine include commercial bread, milk, and seafood.

• The daily minimum dietary requirement for iodine is 150 mcg/day in nonpregnant adults, and 250 mcg/day for pregnant or lactating women

When to Refer

• Refer to endocrinologist for hyperthyroidism, enlarging goiter, suspicious nodules

• Refer to thyroid surgeon for thyroidectomy for cosmesis, compressive symptoms, or thyrotoxicosis in adults with very large multinodular goiters

When to Admit

• Thyroidectomy

• ¹³¹I treatment