(scarred) and merges with surrounding structures,
and acute thyroiditis, which is a serious and
potentially life-threatening bacterial infection of
the thyroid gland that requires emergency medical
treatment.
Symptoms and Diagnostic Path
Sometimes the first indications of thyroiditis are
the symptoms of hyperthyroidism, as the inflam-
mation causes the follicular cells to release a surge
of thyroid hormones into the BLOODcirculation.
When the effect of this surge subsides thyroid hor-
mone levels in the blood drop below normal,
establishing a state of hypothyroidism. The diag-
nostic path begins with blood tests to measure
thyroid hormone and ANTIBODYlevels, and may
include diagnostic imaging procedures such as
ULTRASOUNDor radioisotope iodine reuptake test to
further evaluate thyroid function and the pres-
ence of any nodules or swelling.
Treatment Options and OutlookWhen thyroid symptoms are transitory, as with
silent thyroiditis and often with subacute thyroidi-
tis, HORMONE THERAPYwith thyroid supplement is
not necessary. Nor is it necessary to treat the
hyperthyroid phase, because this is typically of
short duration. Lifelong thyroid supplement hor-
mone therapy becomes necessary when scarring
permanently destroys thyroid follicular cells.
Risk Factors and Preventive MeasuresThe primary risk for autoimmune thyroiditis is the
existence of any other autoimmune disorders.
Silent thyroiditis nearly always follows CHILDBIRTH,
and subacute thyroiditis follows a viral infection.
Knowing of these risks increases the chance of
early diagnosis, which can minimize the course of
the duration. However, there are no preventive
measures for thyroiditis.
See also GRAVES’S DISEASE; THYROID CANCER; THY-
ROID NODULE; THYROID STORM.
thyroid nodule A small growth that develops
within the tissues of the THYROID GLAND. Most thy-
roid nodules (about 90 percent) are noncancer-
ous. Thyroid nodules, like other thyroid disorders,
are significantly more common in women than
men and become increasingly common with
advancing age. Endocrinologists call a thyroid
nodule “hot” when its tissue secretes thyroid hor-
mones and “cold” when it does not. Most malig-
nant (cancerous) thyroid nodules are cold, while
nearly all hot nodules are benign (noncancerous).
Most thyroid nodules do not cause symptoms.
The person may notice a lump on the front of the
neck when looking in the mirror. Often the doctor
detects a thyroid nodule during a ROUTINE MEDICAL
EXAMINATION. Thyroid nodules may oversecrete
thyroid hormones, resulting in symptoms of
HYPERTHYROIDISM. The diagnostic path may include
ULTRASOUND examination of the neck and a
radioisotope iodine reuptake test, which measures
the ability of the nodule to take in iodine. Normal
thyroid tissue uses iodine to synthesize thyroid
hormones. A nodule composed of tissue other
than thyroid tissue (a cold nodule) does not take
up iodine. A fine-needle aspiration (FNA) biopsy,
in which the endocrinologist withdraws a small
tissue sample from the nodule using a thin needle
and a syringe, provides cells for laboratory exami-
nation to determine whether the nodule is cancer-
ous. A single node is more suspicious than are
multiple nodes.
Some thyroid nodules resolve on their own
without treatment. The endocrinologist may pre-
fer to surgically remove a thyroid nodule that is
causing symptoms, including those of hyperthy-
roidism, or that is growing though often chooses a
course of watchful waiting for asymptomatic nod-
ules that biopsy negative for CANCERand are not
growing. Thyroid nodules may occur in THYROIDITIS
(INFLAMMATIONof the thyroid gland) orHYPOTHY-
ROIDISM(underactive thyroid gland).
See also AGING, ENDOCRINE CHANGES THAT OCCUR
WITH; GOITER; THYROID CANCER.thyroid-stimulating hormone (TSH) A peptide
HORMONEthe anterior lobe of the PITUITARY GLAND
synthesizes in response to the HYPOTHALAMUS’s pro-
duction of THYROTROPIN-RELEASING HORMONE (TRH).
TSH subsequently binds with TSH receptors on the
follicular cells in the THYROID GLAND, stimulating
them to synthesize the primary thyroid hormones
TRIIODOTHYRONINE(T 3 ) and THYROXINE(T 4 ), as well as
a number of minor or precursor hormones. TSH
also influences the pituitary gland’s secretion of
PROLACTINand GROWTH HORMONE(GH). TSH levels in164 The Endocrine System