Causes of Hyperthyroidism

Overview

Prior to reading this section, it is helpful to understand the overall structure and function relationship in the thyroid. The causes of hyperthyroidism can be viewed from the functional perspective of the radioactive iodine (RAI) uptake scans. These scans are the best way to evaluate over-production of thyroid hormone, also known as thyrotoxicosis. The diagnostic RAI scan will either show high uptake or low uptake when interpreted in the setting of a clinically hyperthyroid patient. We have a Radioactive Iodine Clinic for our patients.

Distinguishing between the different causes of hyperthyroidism can be difficult and should be left to specialists with training in thyroid disease. The doctors at Houston Thyroid and Endocrine Specialists have diagnosed and taken care of all forms of hyperthyroidism from the common presentations to the rare causes.

There are several major causes for high levels of thyroid hormone. The most common reason for hyperthyroidism in those without prior thyroid disease is Graves' Disease which is an autoimmune disease causing the body's immune system to stimulate the thyroid gland to overproduce thyroid hormone. The reasons why Graves' disease develop is not entirely clear but it does appear to be, in part, genetically passed down in families. In addition to high thyroid levels, Graves' disease can be associated with an enlarged thyroid gland, or goiter, as well with eye disease which may include bulging, painful and watery eyes or double vision and loss of sight.

Another common reason for high thyroid levels are thyroid nodules, or small benign tumors in the thyroid, which are present in an otherwise normal thyroid gland and which overproduce thyroid hormone. This type of hyperthyroidism, due to a hot nodule", may also cause an enlargement of the thyroid gland but does not usually produce significant eye disease. See a comparison of Graves versus Toxic goiters.

Occasionally, high thyroid levels can develop with inflammation and destruction of the thyroid gland, which causes a release of thyroid hormone from destroyed or damaged thyroid cells into the blood stream. This type of hyperthyroidism, called thyroiditis, can develop after an infection, after pregnancy or as part of an autoimmune syndrome and usually only lasts weeks to months. Often this type of hyperthyroidism will resolve on its own but it can occasionally result in low thyroid levels.

Another common cause of hyperthyroidism is overtreatment of hypothyroidism with thyroid hormone replacement. Rarely, high thyroid levels can develop as a side effect of certain types of medications or from a pituitary tumor which can stimulate a normal thyroid gland to overproduce thyroid hormone.