Hypothyroidism

Subclinical or clinical hypothyroidism is the most likely cause of elevated TSH. Hypothyroidism is most commonly primary - i.e., due to failure of the thyroid gland to produce thyroid hormone. The patient may or may not have symptoms with the degree of hypothyroidism reflected in this mild TSH elevation. With untreated primary hypothyroidism, the degree of TSH elevation generally reflects the extent to which circulating thyroid hormone levels are reduced. There are a number of different causes of primary hypothyroidism. The most common are autoimmune thyroiditis or acute viral thyroiditis. Elevations in TSH can also occur with secondary hypothyroidism, i.e., due to pituitary failure to secrete adequate amount of TSH resulting from hypothalamic or pituitary disease. An altered form of TSH with reduced biologic activity is often produced in this condition. Since it is less active, slight elevations in the plasma TSH can occur.