Hypothyroidism

Excerpt

Hypothyroidism results from low levels of thyroid hormone with varied etiology and manifestations. Hypothyroidism is primarily categorized as primary and secondary (ie, central) hypothyroidism. In primary hypothyroidism, the thyroid gland cannot produce adequate thyroid hormone. The less commonly seen secondary or central hypothyroidism occurs when the thyroid gland functions normally; however, hypothyroidism results from the abnormal pituitary gland or hypothalamus function. Untreated hypothyroidism increases morbidity and mortality. In the United States, autoimmune thyroid disease (ie, Hashimoto thyroiditis) is the most common cause of hypothyroidism, but globally, lack of iodine in the diet is the most common cause.

The presentation can vary from an asymptomatic patient in whom hypothyroidism is only recognized on routine blood work to myxedema coma, which is an extreme presentation of this condition. Classic clinical features, including cold intolerance, puffiness, decreased sweating, and skin changes, may not always be present. A serum TSH level is typically used to assess for primary hypothyroidism in most patients initially. Characteristic laboratory findings of hypothyroidism include elevated TSH levels and low free T4 levels. Today, the diagnosis of hypothyroidism is easily made by the use of simple blood tests and can be treated with exogenous thyroid hormone.