What are the causes of hyperthyroidism?
Hyperthyroidism causing symptoms
(thyrotoxicosis) can be primary, secondary, or tertiary.
In primary hyperthyroidism, the thyroid
produces T3 and T4 independently of stimulation by TSH.
The most common cause of hyperthyroidism is Graves’ disease.
This typically occurs in women 20–40 years of
age. In this disease, autoantibodies to thyroid TSH receptors result in
stimulation of hormone production. Thyroiditis also causes release of thyroid
hormones and may be either subacute (probably viral infection) or acute
suppurative (bacterial infection). Toxic solitary nodules and toxic
multinodular goiters may cause primary hyperthyroidism. A rare cause of primary
hyperthyroidism is a molar preg-nancy secreting chorionic gonadotropin, which
has TSH-like activity. The laboratory abnormalities in primary hyperthy-roidism
are elevated levels of T3 and T4 and low levels of TSH.
In secondary hyperthyroidism, the pituitary
produces excessive TSH, independent of stimulation by TRH. Pituitary adenomas are the most common cause of
secondary hyper-thyroidism. The laboratory abnormalities in secondary
hyperthyroidism are elevated levels of TSH, T3 and T4,
but reduced levels of TRH.
Tertiary hyperthyroidism results from excessive
secre-tion of TRH. The laboratory abnormalities in tertiary hyperthyroidism are
elevated levels of TRH, TSH, and T3 and T4.