Thyroid Monograph - FreeCE

The most common cause of hyperthyroidism, accounting for 60 to 80 percent of
cases, is Graves’ disease. 10 This is an autoimmune disease caused by an
antibody that binds to and activates the TSH receptor and stimulates the gland to
synthesize and secrete excess thyroid hormone. Autonomous production of
thyroid hormone occurs when thyrocytes function independently of TSH receptor
activation, which could result from a benign thyroid adenoma or nodules from a
toxic multinodular goiter. Toxic adenomas are common in younger patients and
in iodine-deficient areas. 11 Toxic multinodular goiter (also known as Plummer
disease) accounts for about 15 to 20 percent of hyperthyroidism cases and can
be 10-fold more common in areas where there is iodine deficiency. 11 This also
occurs more commonly among elderly patients with a long-standing goiter. 12
Thyroiditis is an inflammatory condition that could cause transient excess
secretion of thyroid hormones. This includes subacute thyroiditis (caused by a
viral infection and may resolve within eight months), lymphocitic thyroiditis,
postpartum thyroiditis (can occur in up to 5 to 10 percent of women 3 to 6 months
following delivery), radiation-induced thyroiditis, and pharmacologic thyroiditis
(precipitated by amiodarone). 13 Iodine-induced hyperthyroidism can sometimes
occur after intake of excess iodine in the diet or exposure to radiographic
contrast media, leading to an increase in the synthesis and release of thyroid
hormone in individuals with iodine deficiency and in older patients with preexisting
multi-nodular goiter. 14 Rarely, hyperthyroidism can be caused by tumors
like metastatic thyroid cancer, an ovarian tumor called struma ovarii that
produces thyroid hormone, and trophoblastic tumors that produce beta human
chorionic gonadotropin (β-hCG) which could weakly activate TSH receptors.
C. Other thyroid problems
Thyroid nodules are common and can be seen in as many as 50 percent of all
adults, although this condition is more common in women (6%) than in men
(2%). 4 Most of these nodules are small and benign nodules, and only 5 percent
of the cases represent malignancy.
III. Clinical Features and Diagnosis
Hypothyroidism causes a wide range of clinical presentations, from
asymptomatic to myxedema coma, or multisystem organ failure. These
symptoms can be due to derangements in the metabolic processes or
myxedematous infiltration or accumulation of glucosaminoglycans in the tissue.
In the heart, myxedematous changes can result in heart enlargement, pericardial
effusion, and poor function (ie, decreased contractility, decreased cardiac
output). Decreased thyroid hormones can also lead to increased levels of total
cholesterol and low density lipoprotein (LDL) cholesterol in the bloodstream
because of a change in metabolic clearance. An increase in insulin resistance
may also result. In the gastrointestinal tract, decreased acid secretion,
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