This is a syndrome characterized by hyperactivity of the thyroid gland associated with excess production of thyroxin.
Types of Hyperthyroidism
When hyperthyroidism is associated with goiter and ocular signs, it is called graves disease. When hyperthyroidism is associated with nodular goiter, it is called secondary thyrotoxicosis. Sometimes thyrotoxicosis is associated with autonomous toxic adenoma of the thyroid, and is called Plummer's disease. In case of multinodular goiter, intake of large amounts of iodine during radiographic procedure or during amiodarone therapy may cause toxic changes to appear. This is called jod-basedow disease.
When features of hyperthyroidism are present in the absence of goiter, it is called masked hyperthyroidism. In some elderly patients features of hyper metabolism may be lacking, but patients may develop refractory cardiac failure. This is called apathetic Graves' disease. When the serum T4 level is normal but the serum T3 level is elevated, it is called T3 throtoxicosis.
The Hyperthyroidism Causes
The exact cause of this disease is not known but recent evidence shows that the disease is due to thyroxin homeostasis imbalance between thyroid hormones and peripheral tissues.
Strain, mental stress, and psychic trauma may act via the corticohypothalamic pathway and liberate human specific thyroid stimulators (HSTS). This in turn stimulates the hypothalamus to liberate TRH, which stimulates the anterior pituitary gland to secret TSH to act on the thyroid and produce excessively T3, T4, or sometimes both hormones.
Another protein like TSH also stimulates hormone release and can produce thyroid hyperplasia. This is an immunoglobulin G, which is synthesized by lymphocytes in patients with throtoxicosis and is called "long acting thyroid stimulation" or LATS.