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Causes of Hyperthyroidism

This is an overview section to explain the basic causes of hyperthyroidism

 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.

High radioactive iodine uptake

Low radioactive iodine uptake

Autoimmune thyroid disease #
Hashitoxicosis 
Subacute thyroiditis (de Quervain's thyroiditis)- common
Painless thyroiditis (silent thyroditis, lymphocytic thyroiditis)
Amiodarone
Radiation thyroiditis
Palpation thyroiditis 
Autonomous thyroid tissue**#
Toxic "hot" nodule
Toxic multinodular goiter 
  Exogenous thyroid hormone intake
Excessive replacement therapy with T3 and/or T4
Intentional suppressive therapy for thyroid cancer
Factitious hyperthyroidism     
TSH-mediated
Pituitary resistance to T4 or T3 
Ectopic 
Struma Ovarii- rare
Pt with already known metastatic thyroid cancer after thyroid surgery
HCG mediated 
Trophoblastic disease 
Caveats:
** uptake may be low if there was recent iodine load leading to iodine-induced hyperthyroidism


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. 
 


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