Dr Praveen Ramachandra
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THYROID DISORDERS

The thyroid gland is located inside the neck just below the voice box (larynx). It produces two thyroid hormones, triiodothyronine (T3) and tetraiodothyronine (T4), which regulate how the body uses and stores energy. This is called metabolism. 

Thyroid is controlled by another gland called the pituitary, which is located inside your brain. It produces thyroid stimulating hormone (TSH), which stimulates the thyroid to produce T3 and T4. 


Fig1: Mechanism of thyroid hormone production

Two types of thyroid disorders commonly seen are:

  1.         Hyperthyroidism
  2.           Hypothyroidism
 

Hyperthyroidism

Meaning:

The term hyperthyroidism refers to any condition in which there is too much thyroid hormone in the body. 

                                                                              

                                                                                        Fig 2: Normal vs Enlarged Thyroid


Symptoms:


·         Nervousness                                         

·         Irritability

·         Increased perspiration

·         Heart racing

·         Hand tremors

·         Anxiety

·         Difficulty sleeping

·         Thinning of your skin

·         Fine brittle hair

·         Muscular weakness

·         Frequent bowel movements

·         Weight loss despite a good appetite                               

·         Scanty menses

 
                                       Fig. 3 : Symptoms of Hyperthyroidism

Causes:

  •        Grave’s disease is caused by antibodies in the blood that stimulate the thyroid to grow and secrete too much thyroid hormone.

  •     Toxic nodular or multinodular goiter-one or more nodules or lumps in the thyroid may gradually grow and increase their activity.

  •       Thyroiditis. This condition is caused by a problem with the immune system or a viral infection that damages the thyroid gland and stored hormone is released in blood.

  •     It can also be caused by taking too much thyroid hormone in tablet form.

Diagnosis:

  •     Levels of thyroid hormones- Hyperthyroidism is diagonesed by the levels of thyroxine (T4) and triiodothyronine (T3) and thyroid-stimulating hormone (TSH) in your blood. A high level of thyroid hormone in the blood plus a low level of TSH is confirms excess thyroid hormone. 

  •       Thyroid scan - The scan will differentiate between the different causes of hyperthyroidism. 


Treatment:

No single treatment is best for all patients with hyperthyroidism. The choice of treatment will be influenced by your age, the type of hyperthyroidism that you have, the severity of your hyperthyroidism, and other medical conditions that may be affecting your health. 

Antithyroid drugs


Drugs known as antithyroid agents—methimazole, carbimazole or propylthiouracil (PTU)— block the thyroid gland’s ability to make new thyroid hormone. 

Common minor reactions are red skin rashes, hives, and occasionally fever and joint pains. 

A rarer (occurring in 1 of 500 patients), but more serious side effect is a decrease in the number of white blood cells. Such a decrease can lower your resistance to infection. Very rarely, these white blood cells disappear completely, producing a condition known as agranulocytosis, a potentially fatal problem if a serious infection occurs. If you are taking one of these drugs and get an infection such as a fever or sore throat, you should stop the drug immediately and have a white blood cell count that day. 

Liver damage is another very rare side effect. You should stop the drug and call your doctor if you develop yellow eyes, dark urine, severe fatigue, or abdominal pain. 

Radioactive iodine


The radioactive iodine used in this treatment is administered by mouth, usually in a small capsule that is taken just once. Once swallowed, the radioiodine gets into your blood stream and quickly is taken up by the overactive thyroid cells. Over a period of several weeks to several months (during which time drug treatment may be used to control hyperthyroid symptoms), radioactive iodine damages the cells that have taken it up. Sometimes patients will remain hyperthyroid, but usually to a lesser degree than before. For them, a second radioiodine treatment can be given if needed. More often, hypothyroidism (an underactive thyroid) occurs after a few months. Hypothyroidism can easily be treated with a thyroid hormone supplement taken once a day. 


Radioactive iodine has been used to treat patients for hyperthyroidism for over 60 years. No complications from radioiodine treatment have become apparent over many decades of careful follow-up of patients. 

Surgery 


Your hyperthyroidism can be permanently cured by surgical removal of most of your thyroid gland. This procedure is best performed by a surgeon who has much experience in thyroid surgery. Major complications of thyroid surgery occur in less than 1% of patients operated on by an experienced thyroid surgeon. These complications include damage to the parathyroid glands that surround the thyroid and control your body’s calcium levels (causing problems with low calcium levels) and damage to the nerves that control your vocal cords (causing you to have a hoarse voice). 

After your thyroid gland is removed, the source of your hyperthyroidism is gone and you will likely become hypothyroid. Your thyroid hormone levels can be restored to normal by treatment once a day with a thyroid hormone supplement. 

Beta-blockers 


Beta adrenergic blocking agents block the action of thyroid hormone on your body. They usually make you feel better within hours, even though they do not change the high levels of thyroid hormone in your blood.

 

Hypothyroidism:

Hypothyroidism means you have too little thyroid hormone.


Fig 4: Normal Thyroid vs Atrophied Thyroid

 

Symptoms:

Symptoms may include:                                                    

·         Tiredness /sluggishness                                                           

·         mental depression

·         forgetfulness

·         feeling cold

·         weight gain (only 2-4 kg)

·         dry skin and hair

·         constipation

·         menstrual irregularities

                  
 
                                                      Fig 5: Symptoms of Hypothyroidism

Causes:

·        Autoimmune disease In some people’s bodies, the immune system that protects the body from invading infections can mistake thyroid gland cells and their enzymes for invaders and can attack them.

·        Other causes are- surgical removal of the thyroid glandor radiation treatment for other thyroid illness, congenital hypothyroidism,medicines (amiodarone, lithium, interferon alpha, and interleukin-2), damage to the pituitary gland and rare disorders that infiltrate the thyroid (amyloidosis, sarcoidosis hemochromatosis).


Why care about hypothyroidism? 


In adults, untreated hypothyroidism can lead to poor mental and physical performance. It can affect blood pressure and cholesterol levels and increases risk of heart disease in future. 

Diagnosis of hypothyroidism is especially important during pregnancy to ensure delivery of a healthy baby. Thyroid hormone is important for baby’s brain development upto the age of 2 years. Routine testing of all babies at birth identifies those with hypothyroidism. If treated timely, mental retardation can be prevented in the child. 

Diagnosis:

  •           Hypothyroidism can be diagnosed by simple blood tests: TSH and T4 
  •         If thyroid is not working properly (which is called primary hypothyroidism), pituitary tries to stimulate its function by increasing TSH. So initial stages of primary hypothyroidism, TSH is high and T4 is normal. This is called subclinical hypothyroidism. If thyroid is damaged further, TSH goes higher and T4 starts getting lower. 

  •           If pituitary is not working well, TSH levels are not increased appropriately and T4 is low. This is called secondary hypothyroidism. 

Treatment:

Thyroxine (T4) replacement.

  • Hypothyroidism cannot be cured but can be completely controlled.
  •  It is treated by replacing the amount of hormone that your own thyroid can no longer make, to bring your T4 and TSH back to normal levels.
  • Pure, synthetic thyroxine (T4) works in the same way as a patient’s own thyroid hormone would. Therefore, taking thyroid hormone is different from taking other medications, because its job is to replace a hormone that is missing.
  • The only safety concerns about taking thyroid hormone is taking too much or too little. Your thyroid function will be monitored by your physician to make sure this does not happen.
  • Because it stays in your system for a long time, it is taken just once a day.
  • When thyroid hormone is used to treat hypothyroidism, the goal of treatment is to keep thyroid function within the same range as people without thyroid problems. Keeping the TSH level in the normal range does this.
  • The best time to take thyroid hormone is first thing in the morning on an empty stomach. This is because food in the stomach can affect the absorption of thyroid hormone.
  • If you are taking several other medications, you should discuss the timing of your thyroid hormone dose with your endocrinologist.
  • Do not stop your thyroid hormone without discussing this with your endocrinologist.
  • Most thyroid problems are permanent, and therefore most patients require thyroid hormone for life.
  • If you miss a dose of thyroid hormone, it is usually best to take the missed dose next day morning.
  • It is very important that your TSH levels are checked periodically, even if you are feeling fine, so that your dose of thyroid hormone can be adjusted if needed.

Does thyroid hormone interact with any other medications? 


Taking other medications or products can sometimes cause people to need a higher or lower dose of thyroid hormone: birth control pills, estrogen, testosterone, some anti-seizure medications, some medications for depression, iron, calcium, soy and some cholesterol-lowering medications. For all these reasons, it is important for people taking thyroid hormone to keep their doctor up to date with any changes in the medications or supplements they are taking. 

Taking thyroid hormone during pregnancy: 


Since thyroid hormone is a hormone normally present in the body, it is absolutely safe to take while pregnant. In fact, it is very important for pregnant women, or women who are planning to become pregnant, to have normal thyroid function to provide the optimum environment for her baby. Get your TSH checked when you plan pregnancy. Women who are taking thyroid hormone often need an increased dose of thyroid hormone during their pregnancy, one need to check free T4 and TSH regularly (usually monthly) during pregnancy.