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Hypothyroidism
Autoimmune thyroiditis; Hashimoto's
thyroiditis
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Highlights
What is Hypothyroidism?
Hypothyroidism, also called
underactive thyroid, is a condition
in which the thyroid gland does
not produce enough hormones.
Hypothyroidism can be caused by
the autoimmune disorder
Hashimoto thyroiditis, irradiation
or surgical removal of the thyroid
gland, and medications that
reduce thyroid hormone levels.
Anyone can develop
hypothyroidism, but people ages
50 years and above are at greater
risk, and women are at higher risk
than men. Only a small
percentage of people have fullblown (overt) hypothyroidism. The
prevalence of overt
hypothyroidism in the general
population varies between 0.3%
and 3.7% in the United States.
Many more people have mildly
underactive thyroid glands
(subclinical hypothyroidism).
Symptoms
Symptoms of hypothyroidism
include:
Dry skin
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Thin, brittle hair and
fingernails
Increased sensitivity to cold
Feeling tired
Slow thinking
Constipation
Depression
Muscle and joint pain
Heavier menstrual periods
Hoarse voice
Weight gain or difficulty
losing weight
Fertility problems
In older patients symptoms can
be only fatigue, weakness,
memory loss, or chest pain.
Diagnosis and Treatment
Hypothyroidism can cause serious
complications if left untreated.
Fortunately, it can be easily
diagnosed with blood tests that
measure levels of the pituitary
thyroid-stimulating hormone (TSH)
and the thyroid hormone thyroxine
(T4). Your health care provider
may also want to test for
antithyroid antibodies and check
your cholesterol levels. Based on
these test results, the provider will
decide whether to prescribe
medication or simply see you
again in 6 to 12 months to review
your symptoms with you again, if
necessary.
Medications
The standard drug treatment for
hypothyroidism is a daily dose of
a synthetic thyroid hormone called
levothyroxine. This drug helps
normalize blood levels of thyroid
hormones, T4, and
triiodothyronine (T3). Continuous
treatment with an adequate dose
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of levothyroxine will also normalize
TSH levels.
Many prescription medications
and dietary supplements can
interact with levothyroxine and
either increase or decrease its
potency. (Make sure your provider
knows all the medications and
supplements you are taking.)
Large amounts of dietary fiber can
also interfere with levothyroxine
treatment. People who eat highfiber diets may need higher doses
of the drug. Not taking the
medication as instructed (on an
empty stomach at least 2 hours
after or 1 hour before eating) is
the most common cause of poor
absorption of the medication.
Introduction
Hypothyroidism is a condition in
which the thyroid gland does not
make enough thyroid hormones.
Hypothyroidism is often called
underactive or low thyroid.
The thyroid is a small, butterflyshaped gland located in the front
of the neck. The thyroid gland
produces hormones, notably
thyroxine (T4, 80%) and
triiodothyronine (T3, 20%), which
stimulate vital processes in every
part of the body. These thyroid
hormones have a major impact on
the following functions:
Growth
Use of energy and oxygen
Heat production
Fertility
Metabolism of vitamins,
proteins, carbohydrates, fats,
electrolytes, and water
Immune regulation in the
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intestine
Thyroid hormones can also alter
the actions of other hormones and
drugs.
The thyroid gland, a part of the
endocrine (hormone) system,
plays a major role in regulating the
body's metabolism.
Iodine and Thyroid Hormone
Production
The regulation of thyroid function
is a complex process. It involves 4
hormones and iodine.
Iodine
Iodine is a key element used by
the thyroid gland to make the
hormone thyroxine (T4). Eighty
percent of the body's iodine
supply is stored in the thyroid.
Thyroid Hormones
Four hormones are critical in the
regulation of thyroid function:
Thyrotropin-releasing
hormone (TRH). TRH is
produced in a region of the
brain called the
hypothalamus, which
monitors and regulates
thyrotropin (TSH) levels.
Thyroid-stimulating
hormone (TSH). TSH, also
called thyrotropin, is
secreted by the pituitary
gland. TSH directly affects
the process of iodine
trapping and thyroid
hormone production. When
thyroxine (T4) levels drop
even slightly, the pituitary
gland goes into action to
pump up secretion of TSH so
that it can stimulate T4
production. When T4 levels
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fall, TSH levels increase.
Thyroxine (T4). T4 is the key
hormone produced in the
thyroid gland. Low levels of
T4 produce hypothyroidism,
and high levels produce
hyperthyroidism.
Triiodothyronine (T3).
Thyroxine (T4) converts to
triiodothyronine (T3), which is
a more biologically active
hormone. Only about 20% of
T3 is actually formed in the
thyroid gland. The rest is
synthesized from circulating
T4 in tissues outside the
thyroid, such as the liver and
kidney. Once T4 and T3 are in
the circulation, they typically
bind to substances called
thyroid hormone transport
proteins (thyroid binding
globulins). After having their
effect in various parts of the
body, the thyroid hormones
are later inactivated and the
iodine is recycled to form
new thyroxine.
Click the icon to see an image of
the thyroid.Click the icon to see
an image about thyroidstimulating hormone.
Hypothyroidism
Hypothyroidism occurs when
thyroxine (T4) levels drop so low
that body processes begin to slow
down. Hypothyroidism was first
diagnosed in the late 19th
century, when doctors observed
that surgical removal of the
thyroid gland resulted in swelling
of the hands, face, feet, and the
tissues around the eyes. They
named this syndrome myxedema
and correctly concluded that it
was due to the absence of thyroid
hormones, which are normally
produced by the thyroid gland.
Hypothyroidism is usually
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progressive and irreversible.
Treatment, however, is nearly
always completely successful and
allows a person to live a fully
normal life.
Hypothyroidism is classified as
either overt or subclinical
disease. That diagnosis is
determined on the basis of the
TSH laboratory blood tests:
Levels from 0.45 to 4.5 mU/L
are considered normal. (TSH
results can vary by
laboratory with normal as low
as 0.3 mU/L or as high as 5.5
mU/L.)
Levels from 4.5 to 10 mU/L
indicate mildly underactive
thyroid (subclinical
hypothyroidism).
Levels greater than 10 mU/L
indicate overt
hypothyroidism, which should
be treated with medication.
Subclinical hypothyroidism (mildly
underactive thyroid) is a condition
in which TSH levels have started
to increase in response to an early
decline in T4 levels in the thyroid.
However, blood tests for T4 are
still normal. The person may have
mild symptoms (usually slight
fatigue) or none at all. Mildly
underactive thyroid is very
common and is a topic of
considerable debate among
health care providers because it is
not clear how to manage this
condition.
In many people, subclinical
hypothyroidism eventually
progresses to the full-blown
disorder.
Other factors associated with a
higher risk of developing clinical
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overt hypothyroidism include:
Being an older woman (5% to
10% of women over age 50
have subclinical
hypothyroidism and 2%
women between age 70 and
80 years have overt
hypothyroidism)
Having a goiter (enlarged
thyroid gland)
Having high levels of thyroid
antibodies
Having immune factors that
suggest an autoimmune
condition
Having family members
(mother, sister, aunt) who
have thyroid disease
Causes
Many permanent or temporary
conditions can reduce thyroid
hormone secretion and cause
hypothyroidism. More than 90% of
hypothyroidism cases occur from
problems that start in the thyroid
gland. In such cases, the disorder
is called primary hypothyroidism.
(Secondary hypothyroidism is
caused by disorders of the
pituitary gland. Tertiary
hypothyroidism is caused by
disorders of the hypothalamus.)
The two most common causes of
primary hypothyroidism are:
Hashimoto thyroiditis. This
is an autoimmune condition
(chronic lymphocytic
thyroiditis) in which the
body's immune system
attacks its own thyroid cells.
Overtreatment of
hyperthyroidism (an
overactive thyroid).
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Autoimmune Diseases of the
Thyroid
Hashimoto thyroiditis, atrophic
thyroiditis, and postpartum
thyroiditis are all autoimmune
diseases of the thyroid. An
autoimmune disease occurs when
the immune system mistakenly
attacks the body's own healthy
cells. In the case of autoimmune
thyroiditis, a common form of
primary hypothyroid disease, the
cells under attack are in the
thyroid gland and include, in
particular, a thyroid protein called
thyroid peroxidase. The
autoimmune disease process
results in the destruction of
thyroid cells.
Hashimoto Thyroiditis
The most common form of
hypothyroidism is Hashimoto
thyroiditis, a genetic disease
named after the Japanese doctor
who first described thyroid
inflammation (swelling of the
thyroid gland). Women are more
likely than men to develop this
disease.
Click the icon to see an image of
Hashimoto disease.
An enlargement of the thyroid
gland, called a goiter, is almost
always present and may appear
as a growth in the neck.
Hashimoto thyroiditis is
permanent and requires lifelong
treatment. Both genetic and
environmental factors appear to
play a role in its development.
The other main type of
autoimmune thyroid disease is
Graves disease, which causes
hyperthyroidism (overactive
thyroid).
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Click the icon to see an image of
Graves disease.
Atrophic Thyroiditis
Atrophic thyroiditis is similar to
Hashimoto thyroiditis, except a
goiter is not present.
Riedel Thyroiditis
Riedel thyroiditis is a rare
autoimmune disorder, in which
scar tissue progresses in the
thyroid until it produces a hard,
stony mass that suggests cancer.
Hypothyroidism develops as the
scar tissue replaces healthy
tissue. Surgery is usually required,
although early stages may be
treated with corticosteroids or
other immunosuppressive drugs.
Autoimmune Thyroiditis Due to
Pregnancy
Hypothyroidism may also occur in
women who develop antibodies to
their own thyroid during
pregnancy, causing inflammation
of the thyroid after delivery.
Subacute Thyroiditis
Subacute thyroiditis is a
temporary condition that passes
through 3 phases:
hyperthyroidism, hypothyroidism,
and a return to normal thyroid
levels.
People may have symptoms of
both hyperthyroidism and
hypothyroidism (such as rapid
heartbeat, nervousness, and
weight loss, along with or followed
by depression and fatigue), and
they can feel extremely sick.
Symptoms last about 6 to 8 weeks
and then usually resolve, although
each form carries some risk for
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becoming chronic.
The 3 forms of subacute
thyroiditis follow a similar course.
Painless Postpartum Subacute
Thyroiditis
Postpartum thyroiditis is an
autoimmune condition that occurs
in up to 10% of pregnant women
and tends to develop between 4
to 12 months after delivery. In
most cases, the woman develops
a small, painless goiter. This
condition is generally self-limiting
and requires no therapy unless
the hypothyroid phase is
prolonged. If so, therapy may be
thyroxine replacement for a few
months. A beta-blocker drug may
also be recommended if the
hyperthyroid phase needs
treatment. About 20% of women
with this condition go on to
develop permanent
hypothyroidism.
Painless Sporadic, or Silent
Thyroiditis
This painless condition is very
similar to postpartum thyroiditis,
except it can occur in both men
and women and at any age. About
20% of people with silent
thyroiditis may develop chronic
hypothyroidism. Treatment
considerations are the same as
for postpartum subacute
thyroiditis. Some medications may
cause this type of thyroiditis.
Painful, or Granulomatous
Thyroiditis
Subacute granulomatous
thyroiditis, also called de Quervain
thyroiditis, comes on suddenly
with mild to severe neck pain and
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swelling, and often occurs several
weeks after flu-like symptoms. It
is thought to be caused by a viral
infection and generally occurs in
the summer. It is much more
common in women than men and
is usually a temporary condition.
Treatments typically include pain
relievers and, in severe cases,
corticosteroids or beta-blockers.
After Treatment of
Hyperthyroidism
Many people who receive
radioactive iodine treatments for
an overactive thyroid develop
permanent hypothyroidism within
a year of therapy. Radioactive
iodine is a common treatment for
Graves disease, which is the most
common form of
hyperthyroidism, an autoimmune
condition resulting in excessive
secretion of thyroid hormones.
After treatment for Graves
disease, many people gradually
develop hypothyroidism and need
to take thyroid hormones for the
rest of their lives. Other types of
treatment for overactive thyroid
glands (such as anti-thyroid drugs
or surgery) may also result in
hypothyroidism.
Iodine Abnormalities
Too much or too little iodine can
cause hypothyroidism. If there is a
deficiency of iodine, the body
cannot manufacture thyroxine
(T4). Millions of people around the
world have hypothyroidism
because of insufficient iodine in
their diets. This global public
health issue used to be even more
widespread, but has now been
almost completely resolved due to
salt iodization programs. Too
much iodine is a signal to inhibit
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the conversion process of T4 to
T3. The end result in both cases is
inadequate production of thyroid
hormones. Some evidence
suggests that excess iodine may
trigger the process leading to
Hashimoto thyroiditis.
Thyroid Surgery
People who have complete
removal (total thyroidectomy) of
the thyroid gland to treat thyroid
cancer need lifetime treatment
with thyroid hormone. Removing
one of the two lobes of the thyroid
gland (hemithyroidectomy),
usually because of benign
growths on the thyroid gland,
rarely produces hypothyroidism.
The remaining thyroid lobe will
generally grow so that it can
produce sufficient amounts of
thyroid hormone for normal
function. However, to prevent the
formation of additional nodules,
many doctors recommend thyroid
hormone treatment.
Click the icon to see a series on
thyroid surgery.
People with Graves disease who
have surgery to remove most of
both thyroid lobes (subtotal
thyroidectomy) may develop
hypothyroidism.
Drugs and Medical Treatments
that Reduce Thyroid Levels
Lithium
A drug used to treat bipolar
disorder, has multiple effects on
thyroid hormone synthesis and
secretion. Many people treated
with lithium go on to develop
hypothyroidism and some develop
a goiter. Most people develop
subclinical hypothyroidism, but a
small percentage experience
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overt hypothyroidism.
Amiodarone (Cordarone)
Is used to treat abnormal heart
rhythms, contains high levels of
iodine and can induce hyper- or
hypothyroidism, particularly in
people with existing thyroid
problems.
Other Drugs
Drugs used for treating epilepsy,
such as phenytoin and
carbamazepine, can reduce
thyroid hormone levels.
Interferons and interleukins, which
are used to treat hepatitis,
multiple sclerosis, and other
conditions, can induce either
hypothyroidism or
hyperthyroidism. Some drugs
used in cancer chemotherapy,
such as sunitinib (Sutent) or
imatinib (Gleevec), can also cause
or worsen hypothyroidism.
Radiation Therapy
High-dose radiation for cancers of
the head or neck and for Hodgkin
disease can cause
hypothyroidism up to 10 years
after treatment.
Other Medical Conditions
Several medical conditions involve
the thyroid and can change the
normal gland tissue so that it no
longer produces enough thyroid
hormone. Examples include
hemochromatosis, scleroderma,
and amyloidosis.
Causes of Secondary and
Tertiary Hypothyroidism
In rare instances, usually due to a
tumor, the pituitary gland will fail
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to produce TSH, the hormone that
stimulates the thyroid to produce
its hormones. In such cases, the
thyroid gland shrinks and
secondary hypothyroidism occurs.
Causes of Hypothyroidism in
Infants
Hypothyroidism in newborns
(known as congenital
hypothyroidism) occurs in one in
every 3,000 to 4,000 births. It
usually persists throughout life.
Permanent Congenital
Hypothyroidism
In most cases of permanent
congenital hypothyroidism, the
thyroid gland is missing,
underdeveloped, or not properly
located. In other cases, hormone
production is impaired or the
pituitary or hypothalamus glands
function abnormally. Genetic
abnormalities may be a factor in
congenital hypothyroidism, but in
many cases the cause is
unknown.
Temporary Hypothyroidism in
Infants
Temporary hypothyroidism can
also occur in infants. Possible
causes include various
immunologic, environmental, and
genetic factors, including the
following:
Women who have an
underactive (low) thyroid,
including those who develop
the problem during
pregnancy, are at increased
risk for delivering babies with
congenital (newborn)
hypothyroidism. Maternal
hypothyroidism can also
cause premature delivery
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and low birth weight.
Some of the drugs used to
treat hyperthyroidism
(overactive thyroid) block the
production of thyroid
hormone. These same drugs
can also cross the placenta
and cause hypothyroidism in
the infant.
If a pregnant woman has
untreated hyperthyroidism,
her newborn infant may have
hypothyroidism for a short
period of time. This is
because the excess thyroid
hormone in the woman's
blood crosses the placenta
and signals the fetus not to
produce as much of its own
thyroid hormone.
Iodine deficiency may cause
temporary hypothyroidism.
(Exposure to too much iodine
immediately after birth, for
example from iodinecontaining disinfectants or
medicines, can also cause
thyroid dysfunction.)
Premature birth increases the
risk of temporary
hypothyroidism in the infant.
Children with temporary
congenital hypothyroidism should
be followed up regularly during
adolescence and adulthood for
possible thyroid problems. The
risk for future thyroid problems is
highest when girls born with this
condition reach adulthood and
become pregnant.
Risk Factors
Many people have some degree of
thyroid disease, mostly subclinical
hypothyroidism (mildly
underactive thyroid). Only a small
percentage of people have fullblown (overt) clinical
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hypothyroidism.
Gender
Women are much more likely than
men to develop hypothyroidism.
While hypothyroidism most often
occurs in middle-aged and older
women, it is also common during
pregnancy.
Pregnancy affects the thyroid in a
number of ways. The thyroid gland
may increase in size, and changes
in reproductive hormones and
thyroid hormone transport
proteins can cause changes in
thyroid hormone levels. Pregnancy
also boosts iodine requirements in
both the mother and fetus. In
addition, some women develop
antibodies to their own thyroid
during pregnancy, which causes
postpartum subacute thyroiditis
and can increase the risk of
developing permanent
hypothyroidism.
Age
The risk for hypothyroidism is
greater after age 50 years and
increases with age. Symptoms
may overlap with and be similar to
those of menopause. However,
hypothyroidism can affect people
of all ages.
Family History
Genetics plays a role in many
cases of underactive and
overactive thyroid. Many people
with hypothyroidism have a family
history of thyroid problems,
particularly Hashimoto thyroiditis.
Lifestyle Factors
Smoking affects thyroid function
and significantly increases risk for
thyroid disease, especially
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autoimmune Hashimoto thyroiditis
and postpartum thyroiditis.
Smoking also increases
hypothyroidism's negative effects
on the arteries and heart.
Medical Conditions Associated
with Hypothyroidism
People with certain medical
conditions have a higher risk for
hypothyroidism. These conditions
include:
Autoimmune disorders such
as type 1 diabetes, systemic
lupus erythematosus,
pernicious anemia,
rheumatoid arthritis, celiac
disease, Addison disease
(primary adrenal
insufficiency), and
myasthenia gravis.
Chromosomal disorders such
as Down syndrome and
Turner syndrome.
Eating disorders such as
anorexia nervosa or bulimia
nervosa.
Symptoms
Symptoms of hypothyroidism tend
to develop slowly over a long
period of time and vary widely
from person to person.
Intermittent symptoms that vary
from hour to hour or day to day
are rarely due to thyroid hormone
problems.
Early Symptoms
Common early symptoms of
hypothyroidism may include:
Dry, pale skin
Thin, brittle hair and
fingernails
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Increased sensitivity to cold
Feeling tired
Constipation
Slow thinking
Depression
Muscle and joint pain
Slow heart rate
Heavier menstrual periods
Hoarse voice
Enlarged tongue
Weight gain or difficulty
losing weight
Fertility problems
Later Symptoms
Symptoms of severe, untreated
hypothyroidism may include:
Carpal tunnel syndrome
Puffy "moon" face
Cognitive problems, including
slow speech and difficulty
concentrating
Numbness in fingers and
toes (peripheral neuropathy)
Hair loss
Decreased sense of taste
and smell
Sleep apnea
Milky discharge from breasts
(galactorrhea)
Accumulation of fluid in the
skin and tissues (myxedema)
Decreased heart function
Symptoms in Infants and
Children
In the United States, nearly all
babies are screened for
hypothyroidism in order to prevent
cognitive developmental problems
that can occur if treatment is
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delayed. Symptoms of
hypothyroidism in children vary
depending on when the problem
first develops.
Most children who are born
with a defect that causes
congenital hypothyroidism
initially have no obvious
symptoms. Symptoms that
sometimes appear in
newborns may include
jaundice (yellowish skin),
noisy breathing, and an
enlarged tongue.
Early symptoms of
undetected and untreated
hypothyroidism in infants
include feeding problems,
failure to thrive, constipation,
hoarseness, and sleepiness.
Later symptoms in untreated
children include protruding
abdomen; rough, dry skin;
and delayed teething. In
advanced cases, yellow
raised bumps (called
xanthomas) may appear
under the skin, the result of
cholesterol buildup.
If children with
hypothyroidism do not
receive proper treatment in
time, they may be extremely
short for their age; have a
puffy, bloated appearance;
and have intellectual
disabilities. Any child whose
growth is abnormally slow
should be examined for
hypothyroidism.
Complications
Hypothyroidism increases the risk
for physical and mental problems.
Emergency Conditions
Myxedema Coma
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A rare, life-threatening
complication of untreated
hypothyroidism. Symptoms
include:
Constipation
Delirium
Fluid buildup
Reduced lung function
Seizures
Severe drop in body
temperature (hypothermia)
Slow heart rate
Stupor
Urine retention
Coma
Myxedema coma is uncommon,
but it may develop in untreated
people who are under severe
stress, such as those with an
infection or severe cold, or after
surgery. Certain drugs (such as
sedatives, painkillers, narcotics,
amiodarone, and lithium) may
increase the risk. Emergency
treatment is required.
Suppurative Thyroiditis
A life-threatening infection of the
thyroid gland. It is very rare, since
the thyroid is normally resistant to
infection. People with pre-existing
thyroid diseases, such as
Hashimoto thyroiditis may be at
higher than average risk for
suppurative thyroiditis. It often
begins with an upper respiratory
infection. Symptoms include:
Difficulty swallowing and
speaking
Fever
Neck pain
Rash
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Immediate treatment is required.
Heart Problems
Thyroid hormones, particularly
triiodothyronine (T3), affect the
heart directly and indirectly. They
are closely linked with heart rate
and heart output. T3 provides
particular benefits by relaxing the
smooth muscles of blood vessels.
This helps keep the blood vessels
open so that blood flows smoothly
through them.
Hypothyroidism is associated
with:
Unhealthy cholesterol
levels. Hypothyroidism raises
levels of total cholesterol,
LDL (bad) cholesterol,
triglycerides, and other lipids
associated with heart
disease. Treating the thyroid
condition with thyroid
replacement therapy can
significantly reduce these
levels.
High blood pressure.
Hypothyroidism can slow the
heart rate, reduce the heart's
pumping capacity, and
increase the stiffness of
blood vessel walls. These
effects can lead to high
blood pressure. Everyone
with chronic hypothyroidism,
especially pregnant women,
should have their blood
pressure checked regularly.
Heart failure. Hypothyroidism
can affect the heart muscle's
contraction and increase the
risk of heart failure in people
with heart disease.
Pericardial effusion.
Hypothyroidism sometimes
leads to the buildup of fluid
in the sac that surrounds the
heart, known as a pericardial
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effusion.
The evidence for effects of
subclinical hypothyroidism on
heart disease is mixed. Some
studies, but not all, indicate that
subclinical hypothyroidism
increases the risks for coronary
artery disease, heart failure, and
even stroke. However, many
researchers believe that treatment
of subclinical hypothyroidism will
not help prevent or improve these
problems.
Mental Health Effects
Depression
Common in hypothyroidism and
can be severe. Hypothyroidism
should be considered as a
possible cause of any chronic
depression, particularly in older
women.
Mental and Behavioral
Impairment
Untreated hypothyroidism can,
over time, cause mental and
behavioral impairment and,
eventually, even dementia
(memory loss). Whether treatment
can completely reverse problems
in memory and concentration is
uncertain, although research
suggests that only mental
impairment in hypothyroidism that
occurs at birth is permanent.
Other Health Effects of
Hypothyroidism
The following medical conditions
have also been associated with
hypothyroidism. Often the causal
relationship is not clear in
individual cases. These conditions
include:
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Iron deficiency anemia.
Respiratory problems.
Abnormal kidney function.
Glaucoma.
Headache (hypothyroidism
may worsen headaches in
people predisposed to them).
Thyroid cancer (people with
Hashimoto thyroiditis and
people who received
childhood radiation
treatments to the head or
neck are at higher risk for
this rare form of cancer).
Infertility and Pregnancy
Hypothyroidism can interfere with
fertility and increase the risk for
miscarriage and preterm births.
Many women with overt
hypothyroidism have menstrual
cycle abnormalities and some fail
to ovulate. In women who do
become pregnant, overt
hypothyroidism can affect normal
fetal development.
Women who have a history of
miscarriages often have
antithyroid antibodies during early
pregnancy and are at risk for
developing autoimmune thyroiditis
over time. Postpartum thyroiditis is
a specific type of autoimmune
thyroiditis that develops within the
first year following delivery. It can
cause overactive thyroid
(thyrotoxicosis), followed by
underactive thyroid
(hypothyroidism).
Effects of Hypothyroidism on
Infants and Children
Children of Untreated Mothers
Children born to untreated
pregnant women with
hypothyroidism are at risk for
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impaired mental performance,
including attention problems and
verbal impairment.
Effects of Hypothyroidism
During Infancy
Transient hypothyroidism is
common among premature
infants. Although temporary,
severe cases can cause
difficulties in neurologic and
mental development.
Infants born with permanent
congenital (inborn) hypothyroidism
need to receive treatment as soon
as possible after birth to prevent
intellectual disability, stunted
growth, and other aspects of
abnormal development (a
syndrome referred to as
cretinism). An early start of lifelong
treatment avoids or minimizes this
damage. Even with early
treatment, mild problems in
memory, attention, and mental
processing may persist into
adolescence and adulthood.
Effects of Childhood-Onset
Hypothyroidism
If hypothyroidism develops in
children older than 2 years, severe
intellectual disability is not a
danger, but physical growth may
be slowed and tooth eruption
delayed. If treatment is delayed,
adult height could be affected.
Even with treatment, some
children with severe
hypothyroidism may have
attention problems and
hyperactivity.
Diagnosis
A health care provider will
diagnose hypothyroidism after
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completing a medical history and
physical exam, and performing
laboratory tests on the person's
blood. The standard test for
diagnosing hypothyroidism is to
measure blood levels of thyroid
stimulating hormone (TSH). Based
on the results of the TSH test, your
provider may order additional
thyroid tests.
Physical Examination
The provider will check your neck
for signs of an enlarged thyroid
(goiter), which may be a sign of
Hashimoto thyroiditis. The
provider will also check your
heart, eyes, hair, skin, and
reflexes for signs of
hypothyroidism.
Blood Tests
Blood tests measuring thyroid
hormone and TSH levels are
needed to make a correct
diagnosis. In some cases,
antibody tests are also helpful.
Thyroid-Stimulating Hormone
(TSH)
TSH levels are the most important
indicator of hypothyroidism.
However, certain medical
conditions, such as pregnancy,
can affect thyroid hormone levels.
In general, TSH results indicate
the following:
TSH levels over 10mU/L
indicate overt
hypothyroidism. People will
usually need thyroxine (T4)
replacement therapy.
TSH levels between 4.5 and
10 mU/L indicate mildly
underactive (subclinical)
hypothyroidism. People
should be retested every 6 to
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12 months. The decision to
treat is made on an individual
basis.
TSH levels between 0.45 and
4.5 mU/L indicate normal
thyroid function.
TSH levels under 0.45 mU/L
suggest hyperthyroidism,
which is overactive thyroid,
or overtreated
hypothyroidism.
Thyroxine (T4)
If TSH levels appear abnormal,
your provider may order a free T4
test. Low levels of T4 suggest
hypothyroidism. A high TSH level
and a low T4 level confirm a
diagnosis of primary
hypothyroidism.
Much less commonly, people will
have normal TSH levels but low T4
levels. This combination suggests
secondary hypothyroidism, a
condition where thyroid function is
impaired due to problems in the
pituitary gland.
Antithyroid Antibodies
A test for antithyroid antibodies
may be ordered if your provider
suspects your hypothyroidism is
due to the autoimmune condition
Hashimoto thyroiditis. This test
usually checks for thyroid
peroxidase (TPO) antibody. An
alternate test checks for
thyroglobulin antibodies.
High levels of these antibodies
indicate that the immune system
is attacking the thyroid and may
interfere with its function. If your
test results show high levels of
antithyroid antibodies, but your
TSH and T4 levels are within
normal limits, your provider will
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probably delay treatment until
your thyroid function levels
indicate an underactive thyroid.
Many people with positive thyroid
antibodies never develop overt
hypothyroidism.
Other Blood Tests
Because hypothyroidism is often
associated with high cholesterol
levels, anemia, and other health
problems, your provider may order
other tests to detect them.
Imaging Tests
Ultrasound
An ultrasound test uses sound
waves to visualize the thyroid
gland. It can evaluate swelling in
the thyroid, show if any thyroid
nodules (lumps) are present, and
if they are solid, filled with fluid, or
have signs of cancer. Thyroid
nodules are very common and are
usually benign. The ultrasound
and other imaging tests do not
measure thyroid function.
Click the icon to see an image of
thyroid ultrasound.
More Advanced Imaging Tests
Other tests used for visualizing the
thyroid gland include computed
tomography (CT) scans or
magnetic resonance imaging
(MRI).
Radiologic Tests
Radioactive Iodine Uptake Test
(RAIU Test)
The thyroid uptake test is a
nuclear medicine test that uses a
radioactive iodine tracer. You will
drink a liquid or capsule
containing the radioactive iodine.
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A special gamma probe is placed
on the neck to measure how much
of the tracer the thyroid absorbs
from the blood. A low uptake
indicates hypothyroidism.
Thyroid Scan (Scintigraphy)
Thyroid scintigraphy, or scan, is
another nuclear medicine test. It
provides pictures that help the
provider evaluate the structure
and function of the thyroid gland.
This procedure also uses the
radioactive iodine tracer. A special
gamma camera then takes images
of the thyroid. Thyroid scans may
be performed to evaluate a goiter
(swollen thyroid) or thyroid
nodules. They can help identify
areas of the gland that may have
cancer.
Needle Aspiration Biopsy
Needle aspiration biopsy is used
to obtain thyroid cells for
microscopic evaluation. It may be
useful to rule out thyroid cancer in
people with thyroid nodules,
abnormal findings on a thyroid
scan or ultrasound, or those who
have a goiter that is large or feels
unusual on physical exam. Much
like drawing blood, the provider
inserts a small needle into the
thyroid gland and draws cells from
the gland into a syringe. The cells
are put onto a slide, stained, and
examined under a microscope.
Screening Recommendations
for Hypothyroidism
Professional organizations differ
widely on hypothyroidism
screening recommendations. Most
do not recommend widespread
routine screening for healthy
nonpregnant adults who have no
symptoms. The US preventive
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service (USPSTF) concludes that
the current evidence is insufficient
to assess the balance of benefits
and harms of the thyroid
screening in nonpregnant,
asymptomatic adults.
The American Thyroid Association
and the American Association of
Clinical Endocrinologists
recommend considering screening
for hypothyroidism in patients
older than 60 years. They also
recommend "aggressive case
finding" in women who are
planning pregnancy and in
persons who are at increased risk
for hypothyroidism, such as those
with personal or familial history of
autoimmune disease.
Screening in Pregnant Women
Current guidelines recommend
screening women before or during
pregnancy based on their
symptoms or medical history.
Factors that indicate screening is
necessary include:
History of thyroid disease,
goiter, type 1 diabetes or
other autoimmune illnesses
History of miscarriages
History of head and neck
radiation or surgery
Women with these factors should
have their thyroid checked before
pregnancy, or within the first
weeks of pregnancy, and should
be retested during each trimester.
Screening in Infants
In the U.S., most newborns are
routinely screened for
hypothyroidism using a thyroid
blood test.
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Ruling out Other Disorders
Hypothyroidism can mimic other
medical conditions.
Age-Related Disorders
Some symptoms of
hypothyroidism and aging are very
similar. Menopausal symptoms
often resemble hypothyroidism.
Many other problems related to
aging, such as vitamin
deficiencies, Parkinson and
Alzheimer diseases, and arthritis,
also have characteristics that can
mimic hypothyroidism.
Depression
Drowsiness, fatigue, and difficulty
concentrating are signs of clinical
depression as well as
hypothyroidism. Depression and
hypothyroidism often coexist,
particularly in older women, so
diagnosing one does not rule out
the presence of the other.
Chronic Kidney Disease
Edema, sallow complexion, and
drowsiness may also be present in
chronic kidney disease.
Treatment
Hypothyroidism cannot be cured,
but the condition can be
controlled by taking daily
synthetic thyroxine (T4)
medication, most often for life.
Treating Overt Hypothyroidism
In general, health care providers
prescribe thyroid medication for
people who have TSH levels
above 10 mU/L. The exact dosage
depends on many factors,
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including:
Age.
Weight.
Severity of symptoms.
Presence of other medical
conditions that may benefit
from or be worsened by
thyroid replacement therapy.
Pregnancy status.
Medications that the person
is also taking to treat other
conditions, which may
interfere with absorption of
thyroxine (T4) from the small
intestine.
Treating Subclinical
Hypothyroidism
Considerable debate exists about
whether to treat people with
subclinical hypothyroidism (TSH
levels in the upper range of
normal levels or slightly higher
than normal, normal T4 levels, and
no obvious symptoms). In general,
current evidence does not
support treating most people in
this group.
Providers who recommend against
treatment argue that thyroid levels
can vary widely, and subclinical
hypothyroidism may not persist. In
such cases, overtreatment leading
to hyperthyroidism is a real risk.
Most professional organizations
recommend against treating
subclinical hypothyroidism and
suggest monitoring for changes in
thyroid levels that would warrant
treatment.
Your provider may recommend
treating subclinical
hypothyroidism in the presence of
other factors, including:
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Pregnancy
Infertility
Goiter
Heart disease risk factors,
including high total or LDL
(bad) cholesterol levels
Treatment of Special Cases
Treating Older People
Thyroid dysfunction is common in
older people, with most having
subclinical hypothyroidism. There
is no evidence that this condition
poses any great harm in this
population, and most providers
recommend treating only high-risk
patients. Older people, particularly
those with heart conditions,
usually start with very low doses
of thyroid replacement, since
thyroid hormone may cause
angina or even a heart attack.
People who have heart disease
must take lower-than-average
maintenance doses.
Treating Newborns and Infants
with Hypothyroidism
Babies born with hypothyroidism
(congenital hypothyroidism)
should be treated with
levothyroxine (T4) as soon as
possible to prevent complications.
Early treatment can help improve
cognitive and other
developmental factors. However,
even with early treatment, mild
problems in mental functioning
may last into adulthood. In
general, children born with milder
forms of hypothyroidism will fare
better than those who have more
severe forms.
Oral levothyroxine (T4) can usually
restore normal thyroid hormone
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levels within 1 to 2 weeks. It is
critical that normal levels are
achieved within a 2-week period.
If thyroid function is not
normalized within 2 weeks, it can
pose greater risks for
developmental problems. Infants
should continue to be monitored
closely to be sure that thyroxine
levels remain as consistently close
to normal as possible. These
children need to continue lifelong
thyroid hormone treatments.
Treatment During Pregnancy and
for Postpartum Thyroiditis
Women who have hypothyroidism
before becoming pregnant may
need to increase their dose of
levothyroxine during pregnancy.
Women who are first diagnosed
with overt hypothyroidism during
pregnancy should be treated
immediately, with quick
acceleration to therapeutic levels.
Providers often recommend
treating women who are
diagnosed with subclinical
hypothyroidism while pregnant,
although the benefit is not well
proven.
Women with subclinical
hypothyroidism who are not
treated should be evaluated
throughout the pregnancy to see if
they progress to overt
hypothyroidism. There are no risks
to the developing baby when the
pregnant woman takes
appropriate doses of thyroid
hormones. The pregnant woman
with hypothyroidism should be
monitored regularly (thyroid tests
every 4 weeks during the first half
of pregnancy) and medication
doses adjusted as necessary. If
postpartum thyroiditis develops
after delivery, any thyroid
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medication should be reduced or
temporarily stopped during this
period.
Women who are considering
becoming pregnant should take a
prenatal multivitamin that contains
150 to 200 micrograms of iodine in
the form of potassium iodide or
iodate. (Not all prenatal vitamins
contain this recommended
amount, so check the label.)
Women who are pregnant should
also take a multivitamin containing
150 to 200 micrograms of iodine.
Breastfeeding women need to
maintain a daily intake of 250
micrograms of iodine to ensure
that their infants are provided with
100 micrograms of iodine a day.
Prevention of iodine deficiency
Since iodine is indispensable for
the synthesis of thyroid hormones
in the body, iodine deficiency is a
cause of hypothyroidism. An
adequate dietary intake of iodine
prevents iodine deficiency and
reduces the risk for
hypothyroidism. The following are
U.S. recommended daily
allowance (RDA) or adequate
intake values for iodine:
Birth to 6 months: 110
micrograms per day
7 to 12 months: 130
micrograms per day
1 to 8 years: 90 micrograms
per day
9 to 13 years: 120
micrograms per day
14 years and above: 150
micrograms per day
Pregnant women: 220
micrograms per day
Lactating women: 290
micrograms per day
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Iodine deficiency used to be
prevalent in many countries
worldwide. Iodization of salt
implemented through countrylevel programs has significantly
reduced the number of people
with iodine deficiency worldwide.
However, iodine deficiency
remains the world's most
prevalent, although preventable,
cause of brain damage.
Dietary sources of iodine include:
Fish and seafood
Milk and dairy products
Eggs
Seaweed
Iodized salt and other iodine
fortified foods
Additionally, many multivitamin or
other supplements also contain
the RDA of iodine.
Medications
Thyroid Hormone Replacement
The goal of thyroid drug therapy is
to provide the body with
replacement thyroid hormone
when the gland is not able to
produce enough itself.
A synthetic thyroid hormone
called levothyroxine is the
treatment of choice for
hypothyroidism. This drug is a
synthetic derivative of T4
(thyroxine), and it normalizes
blood levels of TSH, T4, and T3.
Brand Names
A number of levothyroxine brands
are available in different countries
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and regions of the world, such as
Synthroid, Euthyrox, L-Thyroxin,
and others. Before synthetic
thyroid hormones were first
manufactured, hypothyroidism
used to be treated with dried
powder thyroid hormone made
from animal glands. In the past,
manufacturers of synthetic
levothyroxine did not need to
meet as strict standards as in the
production of other drugs. This
resulted in thyroid products with
varying quality and potency. The
FDA has since issued stronger
requirements that have largely
corrected this problem.
Generics versus Brand-Name
Products
The American Thyroid Association
(ATA) recommends the
prescription of brand-name
levothyroxine, or alternatively
maintenance of the same generic
preparation (for example,
maintenance of an identifiable
formulation of levothyroxine). ATA
also advices sticking with the
same brand or preparation, since
potency often varies from one
drug to the next.
T3 and T4 Combinations
Triiodothyronine (T3), the other
important thyroid hormone, is not
ordinarily prescribed except under
special circumstances. Most
people respond well to thyroxine
(T4) alone, which is converted in
the body into T3. In addition, the
use of T3 may cause disturbances
in heart rhythms. Some people
treated only with thyroxine
continue to have mood and
memory problems or other
symptoms, however.
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Combination products containing
T4 and T3, such as liotrix
(Thyrolar), are available, but there
is controversy concerning their
benefits. Research indicates that
T3 and T4 together do not work
better than T4 alone. It does not
appear that combination products
offer any advantage for
normalizing TSH levels.
Levothyroxine Regimens
Levothyroxine needs to be taken
only once a day. Although many
people feel better after only 2 to 3
weeks of treatment, levothyroxine
is slowly assimilated by body
organs, so it usually takes up to 6
weeks before symptoms improve
in adults. The speed at which
specific symptoms improve
varies:
Weight loss, less puffiness,
and improved pulse usually
occur early in the treatment.
Improvements in anemia and
skin, hair, and voice tone
may take a few months.
High LDL (bad) cholesterol
levels decline very gradually.
HDL (good) cholesterol levels
are not affected by
treatment.
Goiter size declines very
slowly, and some people may
need high-dose thyroid
hormone (called suppressive
thyroid therapy) for a short
period.
Levothyroxine can help reduce
blood pressure in people who
have both hypothyroidism and
hypertension, although blood
pressure medications may still be
needed.
Appropriate Dosage Levels
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Initial dosage levels are
determined on an individual basis
and can vary widely, depending
on a person's age, medical
condition, other drugs they are
taking, and, in women, whether or
not they are pregnant. For
example, pregnant women with
hypothyroidism need higher
replacement dosage than normal.
Starting out. Most people
need to build up gradually
until they reach a
maintenance dose. In
uncomplicated cases, the
dose typically starts at 50
micrograms (mcg) per day,
which then increases in 4 to
6 week intervals until
reaching the maintenance
dose which produces normal
TSH levels. Seniors and those
with heart disease may start
at 12.5 to 25 mcg per day. On
the other hand, young adults
who have not had
hypothyroidism for very long
might be able to tolerate a
full maintenance dosage right
away.
Maintenance dose.
Maintenance daily dose for
most people averages 112
mcg, but it can vary from 75
to 260 mcg. If conditions
such as pregnancy, surgery,
or other drugs alter hormone
levels, the person's thyroid
hormone needs will have to
be reassessed.
Daily Regimen
Because thyroid replacement
therapy is usually lifelong, setting
up a regular daily routine is
helpful. Here are some tips to
remember:
Establish a habit of taking
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the medication at the same
time each day. This may help
prevent missed doses. It's
best to take levothyroxine on
an empty stomach usually 30
to 60 minutes before eating
breakfast.
If you miss a dose of your
medicine, take it as soon as
you can. If it is almost time
for your next dose, take your
medicine then and skip the
missed dose. Do not use
extra medicine to make up
for a missed dose.
Fiber and common daily
supplements such as
calcium supplements,
calcium aluminum-containing
antacids or iron can interfere
with levothyroxine
absorption, as can
medications such as proton
pump inhibitors and bile acid
sequestrants (that are used
to lower cholesterol).
Foods like soy and walnuts
can also affect absorption. It
is best to take your thyroid
medication 1 hour before or 2
hours after taking
supplements or eating highfiber foods like oatmeal or
calcium-containing foods like
dairy products.
Annual Evaluation
Many factors can cause changes
that require modifications to
levothyroxine dosages. A dose
that is appropriate one year may
be too low the next. To maintain
normal thyroid levels, some
people may need to take
gradually increasing doses of
thyroid hormone. Your provider will
re-evaluate you 6 months after
your TSH levels have normalized,
and then once a year thereafter.
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Specific factors, such as changes
in health or diet, new medications
for other conditions, or simply
switching brands, can also cause
changes in thyroid hormone levels
that require different doses. If you
change dose levels or
levothyroxine brands, your thyroid
levels should be checked again at
least 6 weeks later.
Monitoring Levothyroxine
Treatment
Because levothyroxine is identical
to the thyroxine the body
manufactures, side effects are
rare. Over- or underdosing is fairly
common, although rarely serious
in the short term.
Symptoms of underdosing are the
same hypothyroidism symptoms
originally experienced and may
include:
Sluggishness, fatigue, mental
dullness
Feeling cold
Weight gain
Constipation
Muscle cramps
Symptoms of overdosing include:
Heart symptoms (rapid or
irregular heartbeat,
palpitations, and wide
variations in pulse; possible
angina or heart failure)
Agitation, tremor,
nervousness, insomnia
Feeling warm, flushed skin,
intolerance to heat
Metabolic symptoms (change
in appetite, weight loss)
Diarrhea
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Side Effects of Overdosing
Overdosing can cause symptoms
of hyperthyroidism. A person with
too much thyroid hormone in the
blood is at increased risk for
abnormal heart rhythms, rapid
heartbeat, heart failure, and
possibly a heart attack if there is
underlying heart disease. Excess
thyroid hormone is particularly
dangerous in newborns, and their
drug levels must be carefully
monitored to avoid brain damage.
Long term overdosing may also
lead to thinning of the bones or
osteoporosis.
Drug Interactions with
Levothyroxine
Many drugs interact with
levothyroxine. Important
interactions include:
Amphetamines
Anticoagulants (blood
thinners)
Tricyclic antidepressants
Anti-anxiety drugs
Arthritis medications
Aspirin
Beta-blockers
Insulin
Oral contraceptives
(estrogens)
Testosterone
Digoxin
Certain cancer drugs
Anticonvulsants (phenytoin,
phenobarbital,
carbamazepine)
Rifampin (antibiotic used to
treat or prevent tuberculosis)
Sertraline (antidepressant)
Iron and calcium
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supplements
Proton pump inhibitors
(which reduce stomach acid)
Bile acid sequestrants (which
lower cholesterol levels)
Large amounts of dietary fiber
may reduce the drug's
effectiveness. People whose diets
are consistently high in fiber may
need larger doses of the drug.
Since thyroid hormones regulate
metabolism and can affect the
actions of a number of
medications, dosages may also
need to be adjusted if a person is
being treated for other conditions.
Even changing thyroxine brands
can have an effect.
People who require much higher
than average doses of thyroxine
to normalize their hormone levels
may need to be evaluated for
several conditions that interfere
with absorption of levothyroxine
from the small intestine, such as
celiac disease and Helicobacter
pylori gastritis. They may also
have had surgery in the past to
remove portions of their
intestines.
Inappropriate Use of Thyroid
Hormone
Thyroid hormone replacement is
sometimes prescribed
inappropriately. It should be used
only to treat diagnosed
hypothyroidism.
Inappropriate uses of thyroid
hormones include to induce
weight loss, to reduce high
cholesterol levels, or to treat socalled metabolic insufficiency.
Vague symptoms suggesting low
metabolism, such as dry skin,
fatigue, slight anemia,
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constipation, depression, and
apathy should not be treated
indiscriminately with thyroid
hormone. Some patients with
severe depression are treated
with thyroid hormone even though
their thyroid blood tests are
normal.
Doctors who specialize in thyroid
disorders are concerned with an
increasing trend of treating people
who have subclinical
hypothyroidism. Overtreatment of
borderline hypothyroidism can be
risky, especially for older people.
No evidence exists that thyroid
hormone therapy is beneficial
unless the person has proven
clinical hypothyroidism.
Indiscriminate use of thyroid
hormones can weaken muscles,
possibly increase the risk for
fractures, and, over the long term,
negatively affect the heart.
Resources
American Thyroid Association
-- www.thyroid.org
Hormone Health Network -www.hormone.org
Endocrine Society -www.endocrine.org
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