Hyperthyroidism

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Chapter 30 Hyperthyroidism

INTRODUCTION

Description: Hyperthyroidism is excess production of thyroid hormone. Hyperthyroidism is three times more common in women and may result in menstrual irregularity or fertility disturbances, or it may complicate pregnancy. It may occur because of Graves’ autoimmune disease (most common) or toxic single or multinodular goiters. Rarely, trophoblastic tumors or dermoid cysts may be the cause.

Prevalence: One of 1000 women.

Predominant Age: 20 to 40 years.

Genetics: Graves’ disease may follow a familial pattern.

ETIOLOGY AND PATHOGENESIS

Causes: Graves’ disease—an autoimmune disease in which thyroid-stimulating immunoglobulins bind to thyroid-stimulating hormone (TSH) receptors mimicking the action of thyroid-stimulating hormone and causing excess secretion of triiodothyronine (T₃) and thyroxine (T₄). Goiter and exophthalmos are common. Toxic single or multinodular goiter—one or more autonomous benign nodules that slowly grow. Exophthalmos and myxedema are generally absent.

Risk Factors: Family history, other autoimmune disorders, and iodine deprivation followed by replacement.

MANAGEMENT AND THERAPY

Nonpharmacologic

General Measures: Evaluation, education about the need for continuing therapy, beta blockers for symptoms of tachycardia or tremor.

Specific Measures: Antithyroid medication, therapeutic radioiodine, surgical reduction of thyroid or excision of nodules.

Diet: No specific dietary changes indicated. Maintain adequate calories to avoid weight loss.

Activity: No restriction, as tolerated.

Patient Education: Education regarding need for compliance with medication and follow-up; American College of Obstetricians and Gynecologists Patient Education Pamphlet AP128 (Thyroid Disease).

Drug(s) of Choice

For thyrotoxic crisis—propylthiouracil (PTU) 15 to 20 mg PO every 4 hours during the first day in addition to other therapies.

Initial treatment: PTU 30 to 300 mg PO three times daily (no more than 300 mg/day during pregnancy), maintain at 25 to 300 mg PO two times daily, methimazole (Tapazole, MMI) 15 to 60 mg PO daily, maintain at 5 to 30 mg PO daily; radioiodine therapy: sodium iodine (I¹³¹); adjunctive therapy: propranolol (Inderal) 40 to 240 mg PO daily.

Contraindications: Radioiodine therapy is contraindicated in pregnancy (may cause fetal hypothyroidism or malformation). Propranolol is contraindicated in the presence of congestive heart failure, asthma, chronic bronchitis, and hypoglycemia and during pregnancy.

Precautions: Both PTU and methimazole may cause agranulocytosis, dermatitis, or hepatotoxicity.

Interactions: PTU may potentiate the actions of anticoagulants.

Alternative Drugs

Ipodate sodium (Oragrafin) 0.5 g PO four times daily.

FOLLOW-UP

Patient Monitoring: Normal health maintenance, follow thyroid function test twice yearly. After radioiodine therapy, thyroid function should be checked at 6 and 12 weeks, 6 months, and then yearly.

Prevention/Avoidance: None.

Possible Complications: Hypothyroidism after medical therapy, vision change or loss caused by ophthalmopathy, pretibial myxedema or cardiac failure, muscle wasting and proximal muscle weakness. Surgical therapy—hypoparathyroidism, recurrent laryngeal nerve damage, hypothyroidism.

Expected Outcome: With early diagnosis and adequate treatment, a good outcome is expected.

MISCELLANEOUS

Pregnancy Considerations: Difficult to diagnose in pregnancy. Increased risk of spontaneous abortion. Thyrotoxicosis often improves during pregnancy only to relapse postpartum—must be alert for this possibility. Any goiter is abnormal. Doses of PTU and methimazole must be reduced. Radioiodine therapy is contraindicated.

ICD-9-CM Codes: Based on cause.

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