Definition and Causes:
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clinical state defined as decreased production of thyroid hormone,
by the thyroid gland resulting in deficiency of circulating hormone
which regulates essential functions such as heart rate, digestion,
physical growth, and if left untreated, leads to multiple organ and
Hormone is a chemical released by the cells and function as
messenger that transport signals to other cells. Thyroid gland is
situated in the lower part of the neck. It lies in front of the
wind pipe (or trachea; tra-key-ah) below the Adams apple.
gland produces 2 thyroid hormones called thyroxine (abbreviated T4)
and triiodothyronine (abbreviated T3). The release of these
hormones is partly regulated by
- Other glands such as the pituitary and hypothalamus, situated
within the brain, and
- By the circulating thyroid hormones itself via negative
feedback (the latter refers to the ability of a circulating hormone
to switch off its own production to avoid excess levels
or increase production in case of deficiency)
Hypothalamus (an area at the base of the skull within the brain)
release a hormone known as thyrotropin releasing hormone (TRH).
rate of production is controlled by amount of hormone circulating
within the body, and in turn by the pituitary glands.
Insufficient amount of hormone triggers increase release of
Excess amount of hormone triggers decrease release of TSH.
1) Hashimoto's thyroiditis:
Most common cause of hypothyroidism is an autoimmune disease in
which the body's immune system attacks the thyroid tissue and
develops antibodies to an enzyme called thyroid peroxidase (anti-
TPO antibodies). It usually runs in families and is 5-10 time more
common in females.
It is identified by detecting anti-TPO antibodies in the blood or
by performing a thyroid scan.
2) Treatment of hyperthyroidism:
Individuals producing thyroid hormone in excess (hyperthyroidism);
when treated with anti-thyroid drugs to normalize the thyroid
levels, may result in permanent hypothyroidism.
3) Radiation therapy:
Used to treat head and neck cancers may have effect on the thyroid
gand and may cause hypothyroidism.
4) Thyroid surgery:
If the gland is removed totally or partially; it may result in
decreased or no production of thyroid hormone resulting in
5) Pituitary or hypothalamic disease:
Any defect in signaling the thyroid gland; to produce thyroid
hormone by the pituitary or hypothalamus may result in deficient
6) Severe iodine deficiency: cause
To treat psychiatric disorder such as lithium may cause
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Clinically the disease varies from one patient to the other
depending upon cause, duration and severity of the hypothyroid
state. Since thyroid hormones influence most organs, tissues and
cells of the body, there can be a wide spectrum of sign and
symptoms in this disorder (see figure).
Note: An endocrinologist (doctor specializing in
hormonal diseases) would most likely recognize the subtle
manifestations and would be more skilled to do physical thyroid
gland examination. Consultation is recommended for:
- Patients of age ≤18 years
- Patients who do not respond to treatment
- Pregnant patients
- Cardiac patients
- Structural changes in the thyroid gland
- Presence of other endocrine diseases
Investigations and Treatment:
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History and Physical:
Although history and physical examination will provide definitive
information in severe cases, but asymptomatic individuals with
non-specific signs and symptoms may present.
disease should be considered in older females and in pregnancy.
Common symptoms may include the following:
- Dryness of skin
- Hoarseness of voice
- Cold intolerance
- Weight gain
- A blood test is always needed to confirm the diagnosis
- The measurement of thyroid hormone is usually decreased, unless
it is early in disease course
- Thyroid stimulating hormone (TSH) is measured in the early
phase which should be elevated
the hypothyroidism is confirmed the underlying cause of the disease
is determined by:
- Patient's symptoms
- Local thyroid gland examination
- Presence/ absence of antibodies
MRI of the brain:
This does not use x-rays. Instead MRI uses magnetic fields over the
body. The device looks like a long cylindrical tube. Patients will
lie on a table that slides into the hollow tube. Computer analysis
of magnetic fields within the machine can generate images of the
internal structures of the body's organs, including the brain. MRI
of the brain will show the normal structures, plus any area(s) of
brain injury caused by the inflammation, tumors, etc. Patients must
lie still inside a MRI machine for about a 30-45 min. In some
circumstances a dye might be injected into the veins (enhanced MRI)
just before the scan to help improve detection of abnormalities.
Patients who complain of claustrophobia or discomfort may be given
a mild sedative to help relax prior to MRI scanning.The test may be
advised by the doctor to exclude other causes if necessary.
Goal: Restore normal thyroid state.
Treatment: Is individualized, considering age,
weight cardiac status
Monitoring: Every 6 to 8 weeks until TSH is
normalized, then at 6 months, then annually
Agent of choice:
- Levothyroxine once daily, on an empty stomach
Medical conditions that may interfere with thyroid hormone
- GI malabsorptive disorders
- Previous small-bowel bypass surgery
Risk Factors and Prevention:
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- Females ≥50 years of age
- Family history of autoimmune disease
- Previously treated with anti-thyroid medication or had
- Received radiation therapy to the head or neck region for
- If thyroid have been removed surgically
- Have an autoimmune disease such as diabetes
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- Thyroid hormone replacement therapy continues for life
- Usually thyroid levels return to normal with proper
most severe form of hypothyroidism "myxedema coma" is a rare
complication, caused by an infection, illness, exposure to cold, or
certain medications in people with untreated hypothyroidism.
Myxedema coma can result in death.
Alert: Seek medical help immediately in case
- Chest pain
- Symptoms which are getting worse
- Newly developed symptoms