THYROID GLAND

THYROID GLAND

                     Dr K.P. Paulose

         

Like liver,heart,Kidney and brain,thyroid is an organ,which has a specific role. All human beings have thyroid and normal thyroid  weights 15-25 grams. It is located in front of the neck,just below the voice box and it has the shape of a butterfly.

Thyroid Gland structure

          Thyroid gland belongs to the group endocrine glands’,including pituitary gland in the brain, parathyroid glands embedded in the thyroid  glands, pancreas in the abdomen and sex glands like ovary in females and testes in males. They are called endocrine glands because their secretions called’ hormone directly pushed to circulation; with out the help of ducts. In males the thyroid cartilage in front of the neck is easily visible on swallowing and the gland is situated below the thyroid cartilage. The thyroid cartilage is otherwise called Adam’s apple.

          Thyroid gland starts functioning even before birth and two hormones  it secretes,namely T3 and T4 are very vital for physical and mental growth of all human beings. Thyroid is the only organ,which secretes hormones with the help of iodine.

          Tri-iodo thyronine is called T3 and tetraiodo thyronine is called T4 because these hormones contain 3 and 4 atoms of iodine in each molecule. The hormone secretion of thyroid gland is under the influence of a trophic hormone secreted by the master gland of the body called pituitary,labelled as TSH or Thyroid stimulating hormone. Pituitary gland situated in the base of the brain is called the master gland because it secretes many other trophic hormones which influence endocrine glands like adrenals, ovaries and testes. Four small glands called para thyroid glands which secrete a hormone called” Parathormone” (PTH) necessary for calcium metabolism/ bone growth are also embedded in the thyroid gland. Sometimes during thyroid surgery these parathyroid glands are accidentally removed resulting in “hypocalcaemia”{low calcium level in blood).

          Thyroid hormones: They are called T3 and T4 and these two hormones are required at every  minute by every organ,every tissue and every cell in the body. They control various metabolic activities in the body, which are essential for energy,growth and development. They should be secreted by thyroid in specific quantities and if the gland produces them less than or more than the requirement, it leads to certain complications.  They need to be diagnosed and treated in time. Some special cells of the thyroid gland also secrete a hormone called’ calcitonin’ which brings down calcium level in the blood.

          Thyroid hormones are necessary for the development of feudal brain and lack of these hormones either in the mother or in the foetus leads a poor development of  the brain of the child.

          The role of iodine in Thyroid: Iodine plays an important role in thyroid function because the thyroid hormones are made up of iodine. Iodine deficiency or excess leads to thyroid disorders. Iodine is obtained from the diet and the dietary content depends on the iodine content in the soil and water in a particular location. Thus, supplementation of iodine in salt or bread is suggested as a therapy to compensate iodine deficiency in iodine deficient ares. In India,30-40% of the areas is known to be iodine deficient(low iodine in water).

          Daily requirement of iodine is about 100-150 mcg, which is derived from water, vegetables and fish. Iodine is an essential component of both thyroid hormones. T3 is more potent than T4. Poor iodine content in water as in Sub Himalayan regions, Andesmountainous areas( South America) leads to goiter in people living there( endemic goiter) and cretinism (poor development of children). This is the reason why iodized salts are recommended for daily use to prevent such goiters.

What is a thyroid disorder?

There are basically two types of thyroid disorders:

1.Abnormal size and structure of the gland (goitre with or without nodules)

             

      Goitre may or may not have an associated thyroid dysfunction.

Nodules may be single or multiple. Cancerous growth may present as nodules. Painful thyroid gland enlargement may be seen in inflammatory conditions( Thyroiditis). The term goitre means only an enlargement of thyroid which is benign.

2.Abnormal function of the gland. (Under or over function and it may happen even with out a goitre). 

            Though both causes concern, they require different diagnostic tests and evaluation. Under function of thyroid leading to low production of thyroid hormone is called Hypothyroidism (Myxedema) and over function of thyroid leading to increased production of thyroid hormones  is called Hyperthyroidism ( Graves

Disease). Transient hyper function may be seen Thyroiditis.

Goitre:

          

 Enlarged thyroid gland is called goitre and the enlarged gland may or may not have nodules (lumps) in them. A nodule is the enlargement of a part of the gland. In certain individuals more than one nodule may be present and the size of the goitre at times could be 100 times that of the weight and size of the normal gland. When there are multiple nodules it is called “multi nodular goitre” and single nodules are called” solitary nodular goitre” Many say after looking at your enlarged thyroid.” You have got thyroid, so show it to a  doctor” It is not that you get thyroid enlargement overnight. But any abnormal swelling or enlargement should be shown to a doctor because it could be”Cancer”. They recommend certain studies like ultrasound scanning needle aspiration etc. to rule out malignancy(Cancer)

          About 150 million people in India are at risk of developing benign goitre. Because of iodine deficiency, 54 million Indians are suffering from goitre and 6.6 million are having mild neurological defects, 2.2 million overt cretins are there in India. Even in Kerala, there are pockets of endemic goitre especially in the hilly districts of Kottayam and Idukki.

          In primary hyperthyroidism(due to primary disease of thyroid) T3 T4 values are increased with low TSH while in Primary Hypothyroidism T3 T4 vales are low with high TSH (See Table). It is called primary because pituitary diseases(hypo function or hypo-function as in pituitary tumors)  can also produce hyperthyroidism/hypothyroidism( secondary thyroid disorders) and in these patients although the symptoms may be the same as primary laboratory values are different.

          Normally the thyroid hormones circulated in blood are in the bound form (bound with proteins,more than 99% with a small fraction in the free form. In pregnancy the binding proteins are otherwise increased and hence Free T3 and Free T4 estimation is done to assess the thyroid function.

LAB RESULTS

          Hyperthyroidism (primary)

          Hypothyroidism(primary)

          Pituitary Hyperthyroidism

          Hypopituitarism

          Thyroid Dysfunction

Like any other organ, thyroid too has functional abnormalities. They lead to:

·        Low thyroid hormone production or hypothyroidism or

·        Excess thyroid hormones production or hyperthyroidism

These disorders can be diagnosed within 2-3 hours using simple laboratory blood tests. Once diagnosed they can be brought to perfect normalcy using certain drugs within a week or a month.

 Testing for thyroid function: When you in for your family doctor all relevant complaints, the doctor suspects the possibility of thyroid dysfunction. To confirm or  rule out a thyroid disorder, he sends you to a laboratory to get some basic thyroid tests done called T3,T4 and TSH. These tests, if done, will reveal the exact concentration of the hormones circulating in the blood and a definitive diagnostic conclusion can be arrived at.

Hyperthyroidisma

The major role of the thyroid gland is to produce two thyroid hormones T3 and T4, which control the growth and metabolic rate. These  hormones have their influence on every tissue, every organ and every cell in the body and their levels in blood are important in keeping the metabolic normalcy, If thyroid over functions, it will secrete more hormones(more than the required quantities) and additional load of thyroid hormones will stimulate and  promote certain unwanted metabolic events resulting in certain signs and symptoms and such a patient is known to have hyperthyroidism. Once diagnosed these patients are given medicines which reduce the output of hormones by thyroid and bring normalcy within weeks to months of beginning of therapy. The tremors in treatment for hyperthyroidism, however,is not as easy as that of hypothyroidism and you should consult your clinician to know the merits and limitations of various modes of treatment for hyperthyroidism.

Symptoms of hyperthyroidism:

Due to increased metabolic activities one may experience nervousness, irritability, thinning of skin,fine brittle hair,muscular weakness, hands,increased  bowel movements,increased her rate,loss of weight and in women a delayed or scanty menstrual periods. Enlarged thyroid gland and protruding eyeballs are also noticed in some patients.

Treatment of hyperthyroidism is of 3 types

a-Drugs  like nermercazole to block the excess secretion of thyroid hormones (Tablet forms)

B)Surgery-removal of a significant portion of the hyperactive gland- subtotal thyroidectorny- so that the excess secreation can prevented.

c- Radioactive iodine- oral administration

This facility is available only in specialised centres handling radioisotopes. An isotope of iodine(1-131) which emits radiation is administered to the patient orally in liquid or capsule form. This iodine will go to the thyroid gland and the radiations emitted will destroy the excessively acting thyroid cells. This procedure will be cheaper than surgery in private institutions. Radiations may be allfa,beta or gramma. Although 1-131 emits Beta and grama radiations,the Beta radiations are the one which destroy the overactive thyroid cells.

Hypothyroidism

When the production of thyroid hormone decreases below the body’s need,it results in certain signs and symptoms, a clinical condition called hypothyroidism. In such patients, the laboratory tests indicate a below normal T3, a below normal T4 very high TSH levels.

 When hypothyroidism occurs with puffiness of face without any obvious thyroid enlargement it is called myxedema. Hypothyroidism can also occur in goitre with multiple nodules (multi nodulaar goitre)

The importance of estimation of  free T3 and T4 in pregnancy is mentioned before.

What causes Hypothyroidism?

The most common cause of hypothyroidism is chronic autoimmune Thyroiditis (Hashmoto’s Thyroiditis), a condition characterized by inflammation and damage to the thyroid tissue. The gland partly or  completely fails to synthesis the required quantities of thyroid hormones. Other causes of hypothyroidism  include:

·        Surgical removal of the thyroid gland either for hyperthyroidism or thyroid Cancer.

·        * Radioactive iodine treatment

·        A deficiency in dietary iodine consumption(cretinism)

·        Genetic thyroid absence or function failure or defect in hormone synthesis.

The signs and symptoms of Hypo-thyrodism:

The symptoms of hypothyroidism are mainly dependent on the amount of decrease in thyroid hormone and duration of time that the decreased level has been present. For most patients, the symptoms are mild and can often be confused with menopause or stress. The symptoms may include-

·        Fatigue and muscle swelling or cramps

·        Weight gain

·        Dry skin and cold intolerance

·        Coarseness or loss of hair

·        Depression

Hoarseness

·        Goitre enlarged thyroid causing a lump in the neck

·        Constipation

·        Memory and mental important

·        Infertility or miscarriages

Pregnancy and Hypothyroidism:

Thyroid disorders can sometimes cause unexplained infertility or miscarriages particularly early in pregnancy. Therefore,thyroid function tests are often done as a routine part of evaluating a patient,who may have problems with pregnancy. Untreated hypothyroidism is known to give disturbances in sex and fertility in men also.

          During pregnancy, the requirements of thyroid hormone may increase, and should be monitored closely in the first and second trimester. Both the mother and fetus require optimum hormone levels and,in a hypothyroid pregnant patient,the dose monitoring should be done with extra care and more frequently. It is known that the deficiency of thyroid hormones can cause irreversible damage to both physical and mental growth of the fetus.

Body weight and Thyroid:

          What we eat should be converted into energy for a normal life. In hypothyroidism,the energy conversion is reduced. Hence,fat accumulation and weight increase are very common in hypothyroid patients’ However,once diagnosed and treated, the supplemented thyroid hormone tunes up the metabolic pathways and reduces weight to normal. Similarly in hyperthyroidism, loss of weight occurs.

          Excess secretion of TSH by the pituitary gland as in pituitary tumours also results in hyperthyroidism which is called secondary hyperthyroidism (mentioned before)

          Secondary Hypothyroidism

Since thyroid cells are stimulated by TSH, the failure of pituitary to synthesis desired quantity of TSH too results in a deficiency of thyroid hormones. This group of patients will have all the signs and symptoms of hypothyroidism but will not have an elevated TSH level.

Thyroiditis:

          As in the case of other organs inflammation of thyroid gland can occur which is called Thyroiditis ( you have heard about Tonsillitis, Appendicitis, Neuritis etc}. Thyroiditis may be acute due to bacterial infection or sub acute Thyroiditiis, the thyroid gland is painful and tender.. patients will complain of pain in front of the neck and may have associated symptoms of hyperthyroidism.

          There is another type of Thyroiditis called autoimmune Thyroiditis which may be painless, but will cause irregular firm enlargement of thyroid( chronic thyroiditis and may produce hypothyroidism.

          Antibodies against one’s own thyroid cells are produced in the body(autoimmune antibodies) which acts on thyroid cells resulting in hypo function of the thyroid. These antibodies are called anti microsomal antibodies. Sometime antibodies may present without disturbing the thyroid function. The presence of these antibodies in a pregnant woman may lead to the development of post partum Thyroiditis(within 6months of deliver) characterized by painful enlargement of thyroid gland and hyperthyroidism.

          Treatment of Hypothyroidism:  is by replacement therapy with Thyroxine (T4). T4 will be converted to T3 in the tissues and T3 is the potent hormone. T4 is available as 100mcg/50mcg/25mcg. Tablets which are very cheap. Dose may vary up to 300 mcg, and this can be safely given in pregnancy also. One has to monitor T4/T3/TSH during treatment. For most of the patients, the drug has to be continued for life.

          Ultrasound Scan and Isotope Scan:

Ultrasound Scan of neck will give us some idea regarding the anatomy of thyroid gland whether it is enlarged, whether the nodules are cystic(containing fluid) or solid etc.

ultra sound scanning

          Radioisotope scan  involus the administration of a radioisotope orally (iodine) or intravenously( Technetium) which concentrates in the thyroid and can delineate the  functioning areas. Nodules which concentrate more radioisotope (Iodine/Technetium) are called are called cold nodules. Cancer is more common (10%) in single cold nodules.

          Fine needle aspiration Cytology: is an outpatient procedure which involves striking a needle to the thyroid and aspirating fluid from the gland. This fluid will be sent for hypo-pathological examination to exclude malignancy. This is a simple procedure followed universally and has no complications.

Diagnostic Tests in Thyroid Diseases:

          The most effective and efficient way to diagnose thyroid dysfunction is by measuring the blood levels of T3,T4 and TSH. These tests are done using specialized technologies like Chemiluminescence (CLIA), Radio Immunoassay (RIA) and ELISA etc. Additional tests,which may be helpful in determining the etiology of thyroid dysfunction.

          Thyroid antibodies- anti microsomal(AMA)  or anti thyroglobulin (AT) antibodies

Thyroid isotope scan and/or sonogram

Thyroid biopsy(Fine Needle Aspiration Cytology)

Free T3

Free T4

Cancer thyroid

 Thyroid cancer accounts for only 0.4% all cancer deaths and for about 5 deaths per million population in USA each year. Thyroid cancer is reported to be more in Kerala as compared to other states,may be because of the radiation produced by the radioactive elements in the monazite sand found in the coastal areas.

          Thyroid cancer can occur in children, or in elderly people. The diagnosis is by FNAC or by biopsy. Spread to other organs may some times occur especially lymph nodes and lung. The treatment is complete removal of thyroid gland and adjoining lymph nodes if thyroid gland and adjoining lymph nodes if they are involved. Most of the thyroid metastasis to other regions can be treated by high doses of radioactive iodine. Patient has be to isolated and kept in the isolation ward for 5-7 days to avoid radiation exposure to other people in the household or community. There is one type of cancer called medullary carcinoma throid which can occur in families. Many surgeons advise removal of thyroid in patients with thyroid nodule to prevent malignancy in future. Once the thyroid gland is removed, patients have to be on replacement thyroid medications for life.

Who should be tested?

          Some individuals are more likely than others to be a thyroid patient. These include patients with

·        High cholesterol

·        Have lost or gained more than 2 kilos in 2-3 months

·        Who feel exhausted, fatigued and Weak

·        Too low or too high heart beat rates

·        Irregular heart rate

Why women more often hve Thyroid Failure?

In every five thyroid patients, four are women. Child bearing and associated hormonal, immunological and other stresses in them make them to be more prone to thyroid dysfunction.

Diseases associated with Thyroid dysfunction?

          It is known that majority of the patients with autoimmune disorders have an association with thyroid disorders and patients with chronic Thyroiditis have higher incidence of other autoimmune disease,such as:

*Vitiligo

*Rheumatoid Arthritis

*Addison's disease(adrenal gland low function)

*Diabetes Mellitus

*Pernicious anaemia (B₁₂  Deficiency anemia)

10% of patients with type I Diabetes Mellitus develop chronic Thyroiditis in their life time,which may change their insulin requirements. It is therefore important for diabetic patients to be checked for goiter and have their TSH levels monitored regularly. Some patients suffering from depression may have primary hypothyroidism. In addition,patients on Lithium may develop goitre and hypothyroidism.

What are free thyroid hormones?

          T3 and T4 once secreted from thyroid gland join the blood stream and then travel to the target tissues  in the bound forms. In the ccirculation,there are 3 thyroid hormone binding proteins viz, thyroxine binding prealbumin (TBPA) also known as trans-thyretin,and albumin. It is known that more than 99.95% of hormone circulate in the bound from while only less than 0.05% are available in the free form. Research has proved that it is the “ free thyroid hormone moiety” which is metabolically active and therefore for the last two decades,new technologies have been persuaded to get free thyroid hormone measurements. Ideally speaking, FT3,FT4 and TSH should be a better alternative than conventional TFT ( total T3,total T4 and total TSH)

Conclusion

          Thyroid gland enlargement is a very common phenomenon in women in Kerala. 99% are benign enlargement. The incidence of malignancy thyroid is very rare 3-6 new cases//1,00,000 population. So many diagnostic tests are available to assess the function of thyroid as well as the pathological basis of the gland enlargement. Radioisotope tests are contraindicated in pregnancy. Patients who are on thyroid drugs should not stop it without the consent of the treating doctor.

Prof. John Kurakar