Hypothyroidism

Defintion

Hypothyroidism is defined as a clinical state that results from inadequate

production of thyroid hormones.

Hypothyroidism is underactivity of the thyroid gland that leads to inadequate

production of thyroid hormone and a slowing of vital body functions. (Merck

Manual of Medical Information, 2nd Home Edition)

Anatomy and Physiology

Endocrine System

º group of specialized organs and body tissues that produce, store, and secrete chemical

substances known as hormones.

º As the body's chemical messengers, hormones transfer information and instructions

from one set of cells to another.

Thyroid gland

Anatomy

made up of two lobes connected by a

narrow band called isthmus

these lobes are located on either side of the

trachea, inferior to the larynx

appears more red than surrounding tissues =

higly vascular

contains numerous thyroid follicles [small

spheres filled with proteins (thyroglobulin) to which thyroid hormones are attached]

Physiology

main function: secretion of thyroid hormones (T3 and T4) through the regulation of

thyroid stimulating hormone (TSH) from the pituitary gland, which is in turn controlled by

the thyroid stimulating hormone releasing factor (TRF), secreted by the hypothalamus

Iodine: required to synthesize thyroid hormones

Thyroid hormones

o regulate growth, cellular metabolism and energy production

o approximately 90/10 ratio in the thyroid gland

o T4 (thyroxine) : relatively inert and primarily secreted in the thyroid

o T3 (triiodothyronine) : more active than T4, plays a major role in regulating

metabolic activity in the body

o : formed from the breakdown of T4 in the peripheral

tissues

o Once T4 to T3 conversion takes place, cellular membranes are activated to

assist transfer of thyroid hormone into the interior of our cells. Thus, activating various

enzyme pathways to increase energy production and metabolism, protein

synthesis and breakdown of fat and carbohydrates, increased tissue

oxygenation, mineral exchange within cells, and insulin production. In fact, thyroid

hormone activates over 100 enzymes to produce a multitude of bodily functions. Hence,

the main reason that altered thyroid production and function has such a broad range of

negative effects on people's behavior, moods/emotions, energy level, and physical well-

being.

PREDISPOSING FACTORS RATIONALE

RACE

NHANES 1999-2002 reported that the prevalence of hypothyroidism (including subclinical) was higher in whites (5.1%) and Mexican Americans than in African Americans (1.7%). African Americans tend to have lower TSH values. [http://emedicine.medscape.com/article/122393-overview]

SEX Community studies use slightly different criteria for determining hypothyroidism; therefore, female-to-male ratios vary. Generally, thyroid disease is much more common in females than in males, with reports of prevalence 2-8 times higher in females.

[http://emedicine.medscape.com/article/122393-overview]

AGE

The frequency of hypothyroidism, goiters, and thyroid nodules increases with age. Hypothyroidism is most prevalent in elderly populations, with 2% to as much as 20% of older age groups having some form of hypothyroidism. The Framingham study found hypothyroidism (TSH >10 mIU/L) in 5.9% of women and 2.4% of men older than 60 years.3  In NHANES 1999-2002, the odds of having hypothyroidism were 5 times greater in persons aged 80 years and older than in individuals aged 12-49 years. [http://emedicine.medscape.com/article/122393-overview]

GENETICS/FAMILY HISTORYHypothyroidism tends to run in families. [http://www.webmd.com/a-to-z-guides/hypothyroidism-what-increases-your-risk]

PRECIPITATING FACTORS RATIONALE

HYPOPITUITARISM and INADEQUATE RELEASE OF TRH FROM THE

HYPOTHALAMUS

Underactive pituitary and hypothalamus glands results in the deficiency of one or more pituitary hormones including TRH and TSH. TRH (Thyrotropin-releasing hormone) , a tripeptide–pyroglutamic acid-histidine-proline of hypothalamic origin releases TSH after receptor attachment and activation of cAMPase TSH on the other hand is essential for the functioning of the thyroid gland. If it is not produced in normal amounts, the thyroid gland can be affected as it also becomes underactive. [Merck Manual of Medical Information and McGraw-Hill Concise Dictionary of Modern Medicine, 2002.]

IODINE DEFICIENCY The trace mineral iodine — found primarily in seafood, seaweed, plants grown in iodine-rich soil and iodized salt — is essential for the production of thyroid hormones. Too much or too little iodide can cause hypothyroidism. If there is a deficiency of iodide, the body cannot manufacture thyroxine. About 200 million people around the world have hypothyroidism because of insufficient iodine in their diets. Too much iodide is a signal to inhibit the

conversion process of thyroxine to T3. The end result in both cases is inadequate production of thyroid hormones. Some evidence suggests that excess iodine triggers the process leading to Hashimoto's thyroiditis. [http://www.mayoclinic.com/health/hypothyroidism/DS00353/DSECTION=causes and http://www.umm.edu/patiented/articles/what_causes_hypothyroidism_000038_2.htm]

AUTOIMMUNE RESPONSE

The most frequent cause of acquired hypothyroidism is autoimmune thyroiditis (Hashimoto thyroiditis). The body recognizes the thyroid antigens as foreign, and a chronic immune reaction ensues, resulting in lymphocytic infiltration of the gland and progressive destruction of functional thyroid tissue. Up to 95% of affected individuals have circulating antibodies to thyroid tissue. Antimicrosomal or antithyroid peroxidase (anti-TPO) antibodies are found more commonly than antithyroglobulin antibodies (95% vs 60%). These antibodies may not be present early in the disease process and usually disappear over time. [http://emedicine.medscape.com/article/122393-overview]

PREGNANCY

Some women develop hypothyroidism during or after pregnancy (postpartum hypothyroidism), often because they produce antibodies to their own thyroid gland. Left untreated, hypothyroidism increases the risk of miscarriage, premature delivery and preeclampsia — a condition that causes a significant rise in a woman's blood pressure during the last three months of pregnancy. It can also seriously affect the developing fetus. [http://www.mayoclinic.com/health/hypothyroidism/DS00353/DSECTION=causes]

DRUGS Lithium. Lithium, a drug widely used to treat psychiatric disorders, has multiple effects on thyroid hormone synthesis and secretion. Up to 50% of patients who take lithium develop a goiter, with 20% developing symptomatic hypothyroidism, and another 20 - 30% developing hypothyroidism without symptoms.

Amiodarone. The drug amiodarone (Cordarone),

which is used to treat abnormal heart rhythms, contains high levels of iodine and can induce hyper- or hypothyroidism, particularly in patients with existing thyroid problems. Hypothyroidism occurs in 20% of patients and is the more common effect in the U.S. and other countries where dietary iodine is abundant. Hyperthyroidism is a less common effect in these regions.

Other Drugs. Drugs used for treating epilepsy, such as phenytoin and carbamazepine, can reduce thyroid levels. Certain antidepressants may cause hypothyroidism, although this is rare. Interferons and interleukins are used for treating hepatitis, multiple sclerosis, and other conditions. Evidence suggests that these drugs increase antibodies that put patients at risk for hypo- or hyperthyroidism. Some drugs used in cancer chemotherapy, such as sunitinib (Sunent) or imatinib (Gleevec), can also cause or worsen hypothyroidism.

Radiation Therapy. High-dose radiation for cancers of the head or neck and for Hodgkin's disease can also cause hypothyroidism in up to 65% of patients within 10 years after treatment.[http://www.umm.edu/patiented/articles/what_causes_hypothyroidism_000038_2.htm]

IATROGENIC FACTORS

Treatment for hyperthyroidism. People who produce too much thyroid hormone (hyperthyroidism) are often treated with radioactive iodine or anti-thyroid medications to reduce and normalize their thyroid function. However, in some cases, treatment of hyperthyroidism can result in permanent hypothyroidism.

Radiation therapy. Radiation used to treat cancers of the head and neck can affect your thyroid gland and may lead to hypothyroidism.

Thyroid surgery. Removing all or a large portion of your thyroid can diminish or halt hormone production. In that case, you'll need to take thyroid hormones for life.

[http://www.mayoclinic.com/health/hypothyroidism/DS00353/DSECTION=causes]

SYMPTOMS IMPLICATION/RATIONALERESPIRATORY DISTRESS &

DYSPHAGIAOccurs because of the enlargement of the thyroid gland as a compensatory mechanism.

HYPOXIA, MENTAL DETERIORATION, DEPRESSION

Due to decreased cerebral blood flow

REDUCED STROKE VOLUME AND HEART RATE

Due to decreased cardiac output

INCREASED SYSTOLIC BP Due to an increase in peripheral vascular resistanceREDUCED URINE OUTPUT,

INCREASED TOTAL BODY WATER, LOW SERUM SODIUM LEVELS

Due to decreased renal blood flow

WEIGHT GAIN, DECREASED APPETITE, CONSTIPATION

Due to hypometabolism

DELAYED SKELETAL AND TISSUE GROWTH & REPAIR

Due to decreased protein metabolism

SENSITIVITY TO COLD, REDUCED INABILITY TO SWEAT, DRY AND

FALKY SKIN, BRITTLE HAIR

Due to decreased metabolic rate and basal body temperature; in hypothyroidism the body has reduced its ability to form sweat and other secretions from the sebaceous glands

Thyroid gland dysgenesis

Predisposing factors:

Race Age Sex

Genetics

Precipitating factors:

Inadequate release of TRH Iodine deficiency and excess Autoimmune response Atrophy of thyroid gland with aging Radiation of head and neck for

treatment of head and neck cancers Drugs ( e.g. anti-thyroid medications,

lithium) Therapy for hyperthyroidism

(Radioactive iodine and thyroidectomy)

Enzymatic defects

Impaired synthesis of thyroid hormone

Inadequate thyroid hormone levels

Failure of the hypothalamus to produce TRH

No stimulation of the pituitary gland to secrete TSH

Insufficient stimulation of the thyroid gland

Destruction of thyroid tissue

Pathologic changes in the thyroid gland

Suppression of thyroid function

Hypothyroidism

Stroke volume and heart rate

Mental status changes, forgetfulness, depression,

personality changes

Reduced urinary output,Decreased serum Na levels

Respiratory distress, sleep apnea, respiratory muscle weakness

Decreased metabolic rate, decreased appetite, weight gain, constipation, increased cholesterol and triglycerides levels, decreased

absorption of glucose, decreased CHON metabolism, constipation

Fatigue, subnormal temperature, thickening of the skin

Diagnostic Exams

Blood Tests:

Radioimmunoassay .It measures amount of T3 and T4 in the blood. The test is used to confirm diagnosis. Results show low T3 and T4 levels.

TSH Levels. In the typical person with an under-active thyroid gland, the blood level of T4 (the main thyroid hormone) will be low, while the TSH level will be high. This means that the thyroid is not making enough hormone and the pituitary recognizes it and is responding appropriately by making more Thyroid Stimulating Hormone (TSH) in an attempt to force more hormone production out of the thyroid.

Imaging Tests:

Thyroid Scintigraphy. Thyroid scintigraphy, or scan, can be used to determine which areas of the thyroid are producing normal amounts of hormone. The patient drinks a small amount of radioactive iodine or technetium and waits until the substance has passed through the thyroid. Images of a properly functioning thyroid show uniform levels of absorption throughout the gland. Overactive areas show up white, and underactive areas appear dark. Thyroid scans are more likely to be done to evaluate a goiter (swollen thyroid) or thyroid nodules.

Ultrasound. Ultrasound has limited value, but it can visualize the thyroid and specific abnormalities, such as nodules.

If treated: refer to medical and nursing management

Fair prognosis

If not treated: MYXEDEMA COMA

DEATH

Medical Management

The primary objective in the management f hypothyroidism is to restore normal metabolic state by replacing the missing hormone. With the exception of certain conditions, the treatment of hypothyroidism requires life-long therapy.

Pharmacologic Therapy

T3 [liothyronine sodium (Cytomel)]- is available and there are certain indications for its use. However, for

the majority of patients, a form of T4 [levothyroxine sodium (Levoxyl, Synthroid)] is the preferred treatment.

Synthetic levothyroxine (Synthroid or Levothroid) - Preferred preparation for treating hypothyroidism and suppressing

nontoxic goiters.- a more stable form of thyroid hormone and requires once a day

dosing, whereas T3 is much shorter-acting and needs to be taken multiple times a day. In the overwhelming majority of patients, synthetic T4 is readily and steadily converted to T3 naturally in the bloodstream, and this conversion is appropriately regulated by the body's tissues.

Nursing management

Schedule activities to promote rest and exercise as tolerated. Assist with self-care activities.

Monitor patient’s body temperature and report a decrease from patient’s baseline value

Encourage to increase fluid intake within limits of fluid restriction. Provide foods high in fiber.

Monitor bowel movement Monitor RR, depth, pattern, pulse oxymetry and arterial blood gases. Monitor cognitive and mental processes and response of these to medication and

other therapy Provide stimulation through conversation and nonthreatening activities. Orient

patient to time, place, person and situation Explain to the patient and family that change in cognitive and mental function is a

result of disease process Monitor patient for increasing signs and symptoms of hypothyroidism such as

decreased level of consciousness and decreased VS Assist in ventilator support if respiratory depression occurs Administer prescribed medication (thyroxine) with extreme caution

Reposition patient at intervals Avoid use of hypnotics, sedatives, and analgesic agent Explain rationale for thyroid hormone replacement Assist patient to develop schedule and checklist to ensure self-administration of

thyroid hormone replacement Explain the necessity for long-term thyroid replacement therapy

Nursing diagnoses

Activity intolerance related to fatigue Risk for imbalanced body temperature/ Ineffective thermoregulation Constipation related to depressed GI function Ineffective breathing pattern r/t depressed ventilation Disturbed thought process r/t depressed metabolism and altered CV and respiratory

function Deficient knowledge about the therapeutic regimen for lifelong thyroid replacement

therapy

PROGNOSIS:

Good. With treatment, return to the normal state is usual. However,life-long medication is needed.