Hyperthyroidism is a condition of having over-active thyroid gland resulting in the production and secretion of excessive amount of thyroid hormones namely Triiodothyronine and Tetraiodothyronine or Thyroxine.
Thyroid gland is one of the largest glands in human body. It is located at the neck below the thyroid cartilage. Three hormones are secreted from thyroid gland. These hormones are Triiodothyronine(T3), Tetraiodothyronine or Thyroxine(T4) and Calcitonin. T3 and T4 regulates the rate of metabolism thus controlling the overall growth and the functions of various organs. The role of Calcitonin is not yet fully understood, it plays some minor role in calcium metabolism.
The production of thyroid hormones is controlled by Thyroid stimulating hormone or TSH. TSH is secreted from anterior pituitary gland. The secretion of TSH is again controlled by thyrotropin-releasing hormone (TRH) produced by the hypothalamus.
T3 and T4 are produced by the follicular cells present in the thyroid gland under the regulation of TSH. Thyroxine or T4 is produced by attaching four iodine atoms with the tyrosine molecules whereas Triiodothyronine or T3 is produced by attaching three iodine atoms with the tyrosine molecules. So iodine is compulsory for the production of thyroid hormones.
The molecular formula of triiodothyronine is C15H12I3NO4 and the structural formula is
The molecular formula of tetraiodothyronine or thyroxine is C15H12I4NO4 and the structural formula is
The ratio of T3 to T4 secreted into the blood is approximately 1 : 20. T4 is converted to T3 by the presence of the enzyme deiodinases with the reduction of 1 iodine atom.
The normal range of T3, T4 and TSH in blood:
|Sample||Conventional Units||SI Units|
|Total Triiodothyronine or T3||1-7 days: 100 -470 ng/dL8- 364 days: 105 -245 ng/dL1 -9 years: 94 -269 ng/dL10-19 years: 102 -200 ng/dL> 20 years old: 80 -200 ng/dL||Adults:0.8 – 2.0 ng/ml0.9 – 2.8 nol/L|
|Total Tetraiodothyronine or Thyroxine or T4||4.5 – 12.5 µg/dL||58 – 161 nol/L|
|Total Thyroid Stimulating Hormone or TSH||0.5 – 4.70 µIU/mL||0.5 – 4.70 mI/L|
Sign & symptoms of hyperthyroidism: The increased level of thyroid hormone accelerate almost every function of body (since thyroid hormones regulates the rate of metabolism). The extreme symptoms of hyperthyroidism is called thyroid storm and need immediate medical attention. The common symptoms are as follows:
- General weakness and fatigue
- Goiter or enlarged thyroid gland
- Frequent bowel movements
- Nervousness, anxiety, irritability and panic attack like symptoms
- Susceptible to heat, heat intolerance and increased sweating
- Increased appetite yet loss of weight
- Rapid or irregular heartbeat and palpitations
- Irregular menstrual periods in women
- Restlessness and poor concentration
- Fine and brittle hair and prone to hair fall.
- Tremor in hand or fingers
- Enlarged and Protruding eyes
- Disturbed sleep
- Long term untreated hyperthyroidism can lead to osteoporosis
The primary diagnosis of hyperthyroidism is checking the level of TSH, T3 and T4 in blood. Generally decreased level of TSH implies increased level of T3 and T4 but in some cases disease like Euthyroid sick syndrome may be the cause of lower level of TSH.
After confirming the above mentioned test radioactive iodine uptake test and thyroid scan is done together to determine the cause of hyperthyroidism. In radioactive iodine uptake test radioactive iodine is injected or taken orally to measure the amount of iodine absorbed by the thyroid gland. Too much absorption of iodine indicates hyperthyroidism. After that thyroid scan is performed for the visual examination of the thyroid gland.
Treatment or management: Hyperthyroidism is generally treatable and only in very rare cases it can be life threatening. Various ways to treat hyperthyroidism are given below:
Anti-Thyroid drugs: If the symptoms are mild, generally anti-thyroid drugs like Carbimazole, methimazole and propylthiouracil are given as the treatment of hyperthyroidism. These drugs are called Thyrostatics and the function of thyrostatics is to inhibit the production of thyroid hormones.
Beta blockers : Beta blockers are used to reduce the symptoms of hyperthyroidism. It is not used to treat hyperthyroidism, it is generally used to get immediate temporary relief from the various symptoms like anxiety, trembling, and palpitations
Radio iodine treatment: In this treatment radioactive isotope of iodine (iodine-131 or I131) is given orally. Iodine is readily absorbed by thyroid gland and this particular isotope is very potent and emits beta particles. The half life of I131 is 8-13 hours. Beta particles are picked up by the over active follicular cells of the gland which in turn gets damaged, so the thyroid gland becomes partially or fully inactive. After that the required amount of thyroid hormone is given through hormone replacement therapy.
This treatment has practically no side effects but it is not suitable for pregnant or breast feeding women.
Surgery: Surgical removal of full or partial thyroid gland is called thyroidectomy. This is not done extensively because radioactive iodine method is very effective to treat hyperthyroidism. More over, surgery is risky, as it can result in removal of parathyroid glands or of cutting the recurrent laryngeal nerve.