Diagnostic Considerations

Hyperthyroidism

Disorders associated with thyroid hyperfunction include these:

Excessive production of TSH
Abnormal thyroid stimulation (eg, due to Graves disease, trophoblastic tumors)
Intrinsic thyroid autonomy (eg, hyperfunctioning adenoma, toxic multinodular goiter, thyroid malignancy)

About 30-60% of women with hyperemesis gravidarum have gestational hyperthyroidism. This condition is characterized by elevated FT4 values, suppressed TSH levels, minimal thyroid enlargement, variable evidence of clinical hyperthyroidism, and absent thyroid antibodies. Gestational hyperthyroidism is due to the thyroid-stimulation effects of human chorionic gonadotropin (hCG) and is most likely to arise in the setting of elevated hCG concentrations (eg, molar or multiple pregnancies). Treatment is usually not needed because spontaneous recovery occurs after the first trimester.

Disorders not associated with thyroid hyperfunction include these:

Disorders of hormone storage (eg, subacute thyroiditis, thyrotoxicosis phase of chronic thyroiditis)
Disorders associated with an extrathyroidal source of hormone (eg, thyrotoxicosis factitia, ectopic thyroid tissue [struma ovarii, functioning follicular carcinoma])

Hypothyroidism

Thyroid-related conditions include the following:

Thyroprivic conditions (eg, primary idiopathic, postablative, postradiation)
Goitrous conditions (eg, iodine deficiency, drug-elicited disorders, chronic thyroiditis [Hashimoto thyroiditis])

Other thyroid conditions are related to the following entities:

Suprathyroid conditions
Pituitary conditions (eg, Sheehan syndrome)
Hypothalamic conditions (eg, inadequate thyroid-releasing hormone)
Self-limited conditions (eg, withdrawal of suppressive thyroid therapy, PPT)

Effects of commonly used drugs

Creasy and Resnik described effects of commonly used drugs on the results of tests for thyroid hormone. The following is an adapted list of effects and examples of drugs that cause them:

Inhibition of thyroid function - Iodine, lithium, and sulfonylureas
Inhibition of T4 and triiodothyronine (T3) conversion - Glucocorticoids, propranolol, amiodarone, and propylthiouracil (PTU)
Increase in TSH levels - Iodine, lithium, dopamine antagonists, and cimetidine
Decrease in TSH levels - Glucocorticoids, dopamine agonists, and somatostatin
Inhibition of the binding of T4 and T3 to transport proteins - Phenytoin, sulfonylureas, diazepam, furosemide, and salicylates
Inhibition of GI absorption of thyroid hormones - Cholestyramine, ferrous sulfate, aluminum hydroxide, and sucralfate

Differential Diagnoses

Chronic Myelogenous Leukemia (CML)
Graves Disease
Hashimoto Thyroiditis
Hyperthyroidism and Thyrotoxicosis
Hyperthyroidism, Thyroid Storm, and Graves Disease
Hypothyroidism
Subacute Thyroiditis
Thyroiditis, Subacute

Workup

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