Hypothyroidism: Diagnosis and Treatment

Diagnosis

Because clinical presentation is highly variable, diagnosis relies on laboratory testing. Several factors may lead to altered thyroid test results in the absence of thyroid disease. These include malnutrition, chronic illness, diabetic ketoacidosis, drugs, and pregnancy.

Initial laboratory testing includes serum TSH and free T4 levels.

• Serum TSH is increased in primary hypothyroidism. This is the most sensitive test for primary hypothyroidism, but it is less useful for secondary hypothyroidism, in which TSH is usually decreased, but may also be normal or elevated.
• Serum free T4 is decreased.

Further laboratory testing may be useful in selected cases.

• Thyrotropin–releasing hormone is elevated in primary hypothyroidism.
• Thyroid autoantibodies are present in Hashimoto’s thyroiditis.
• Radioactive iodine uptake will be low in cases of hypothyroidism. However, this study is more useful for evaluating cases of hyperthyroidism.
• Elevated cholesterol, triglycerides, and creatine phosphokinase may occur.

Radioimaging can evaluate the size, shape, and iodine distribution of the thyroid gland and evaluate for compression of vital structures.

Fine needle aspirate can confirm the diagnosis and rule out cancer.

Treatment

In most cases, hypothyroidism requires lifelong thyroid hormone replacement (L–thyroxine). The usual regimen begins at 50μg per day and increases by 25 to 50 μg per day every 4 to 8 weeks until a maintenance dose is reached. The dose is adjusted until an appropriate TSH level is attained.

Iodine deficiency is treated with potassium iodide.

Myxedema coma is treated initially with intravenous L–thyroxine, L–triiodothyronine, and corticosteroids, followed by maintenance doses of oral thyroid hormones.