Atlas of pathophysiology, 2 Edition

Part II - Disorders

Endocrine Disorders

Simple goiter

Simple (or nontoxic) goiter is a thyroid gland enlargement that isn't caused by inflammation or a neoplasm, and is commonly classified as endemic or sporadic. Inherited defects may be responsible for insufficient thyroxine (T4) synthesis or impaired iodine metabolism. Because families tend to congregate in a single geographic area, this familial factor may contribute to the incidence of both endemic and sporadic goiters.

Causes

Endemic goiter

·   Inadequate dietary iodine

Sporadic goiter

·   Large amounts of foods containing agents that inhibit T4 production, such as rutabagas, cabbage, soybeans, peanuts, peaches, peas, strawberries, spinach, radishes

·   Drugs, such as propylthiouracil, iodides, phenylbutazone, para-aminosalicylic acid, cobalt, lithium; may cross placenta and affect fetus

Pathophysiology

Goiters can occur in the presence of hypothyroidism, hyperthyroidism, or normal levels of thyroid hormone. In the presence of a severe underlying disorder, compensatory responses may cause both thyroid enlargement (goiter) and hypothyroidism. Simple goiter occurs when the thyroid gland can't secrete enough thyroid hormone to meet metabolic requirements. As a result, the thyroid gland enlarges to compensate for inadequate hormone synthesis, a compensation that usually overcomes mild to moderate hormonal impairment.

Signs and symptoms

·   Enlarged thyroid

·   Respiratory distress

·   Dysphagia

·   Venous engorgement; development of collateral venous circulation in the chest

·   Dizziness or syncope (Pemberton's sign) when the patient raises her arms above her head

Diagnostic test results

Laboratory tests reveal:

·   normal serum thyroid levels

·   high or normal thyroid-stimulating hormone (TSH) levels

·   low-normal or normal T4 concentrations

·   normal or increased radioactive iodine uptake.

Treatment

·   Exogenous thyroid hormone replacement with levothyroxine (treatment of choice)—inhibits TSH secretion and allows gland to rest

·   Small doses of iodide (Lugol's iodine or potassium iodide solution)—commonly relieves goiter due to iodine deficiency

·   Avoidance of known goitrogenic drugs and foods

·   For large goiter that's unresponsive to treatment—subtotal thyroidectomy

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RECOGNIZING TYPES OF GOITERS

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