Encyclopedia of Health and Medicine

Graves’s disease 129
occurs as a consequence of PREGNANCY (when the
body’s need for thyroid hormones increases) or in
EUTHYROID SICK SYNDROME (when a health crisis disrupts
the entire endocrine matrix). A goiter may
cause uniform enlargement of the thyroid gland
(diffuse goiter) or isolated enlargement (nodular
goiter). Though typically a goiter is visible on the
front of the neck, occasionally a nodular goiter
forms on the back of a thyroid lobe, near the end,
pressuring the airway. Among the numerous
causes of goiter are
• iodine deficiency
• HYPOTHYROIDISM (underactive thyroid)
• HYPERTHYROIDISM (overactive thyroid), including
GRAVES’S DISEASE
• THYROIDITIS (INFLAMMATION of the thyroid gland)
• radiation exposure (such as from RADIATION
THERAPY to treat CANCER of the larynx, MOUTH, or
upper chest)
• thyroid nodules (noncancerous growths)
• THYROID CANCER
Hypothyroidism, hyperthyroidism, and thyroiditis
are the most common causes of diffuse
goiter. Thyroid nodules, which are fairly common,
and thyroid cancer, which is relatively uncommon,
are more likely to cause nodular goiter.
Iodine deficiency is rare in the United States
because most table salt is iodized. Symptoms of
goiter may include
• visible swelling on one side or both sides of the
neck
• palpable lump in the neck, especially when
swallowing
• difficulty swallowing or the sensation of something
being stuck in the THROAT
• difficulty breathing, usually with exhalation
Many people also have symptoms of hypothyroidism
or hyperthyroidism, when either condition
is the cause of the goiter. The diagnostic path
includes blood tests to measure the level of thyroid
hormones, ULTRASOUND of the neck, and often
a radionuclide scan or COMPUTED TOMOGRAPHY (CT)
SCAN. Treatment depends on the findings and the
extent to which symptoms interfere with functions
such as swallowing or BREATHING. If surgery
to remove the thyroid gland is necessary (thyroidectomy),
the person will need to take lifelong
thyroid supplementation (thyroid HORMONE THER-
APY). Endocrinologists typically take an approach
of watchful waiting with a goiter that causes no
symptoms and does not affect thyroid function
(thyroid hormone levels are normal).
See also AUTOIMMUNE DISORDERS; LYMPHOMA; THY-
ROID NODULE.
gonadotropin-releasing hormone (GnRH) A
peptide HORMONE, also called luteinizing hormonereleasing
hormone (LHRH), the HYPOTHALAMUS
produces to stimulate the anterior lobe of the PITU-
ITARY GLAND to synthesize and release LUTEINIZING
HORMONE (LH) and FOLLICLE-STIMULATING HORMONE
(FSH). LH and FSH in turn stimulate the gonads, or
sex glands, to produce their respective hormones.
In women the effect stimulates the OVARIES to produce
ESTROGENS and PROGESTERONE, and in men
stimulates the TESTES in men to produce TESTOS-
TERONE. When these sex hormones reach certain
levels in the bloodstream the hypothalamus stops
secreting GnRH, and the gonadotropic cascade
stops—a negative-feedback loop. In women these
levels fluctuate according to the menstrual cycle.
Other hormones may also influence the release of
GnRH.
Doctors sometimes use a pharmaceutical preparation
of GnRH, called a GnRH analog, to treat
ENDOMETRIOSIS. Because its chemical composition is
nearly identical to that of endogenous GnRH, a
GnRH analog binds with GnRH receptors to block
endogenous GnRH binding. This prevents the
release of LH and FSH, and consequently suppresses
the menstrual cycle and OVULATION.
For further discussion of GnRH within the context
of the endocrine system’s structure and function
please see the overview section “The
Endocrine System.”
See also ANTIDIURETIC HORMONE (ADH); GROWTH
HORMONE (GH); INHIBIN; MENSTRUATION; OXYTOCIN;
PROLACTIN; THYROID-STIMULATING HORMONE (THS).
Graves’s disease An autoimmune disorder in
which the body produces antibodies that attack
the THYROID GLAND, producing symptoms of HYPER-
THYROIDISM (overactive thyroid gland). The most