Thyroid status can be of three varieties:
1. Euthyroid or normal condition
2. Hypothyroid or Lower Secretion
3. Hyperthyroid or Increased Secretion
Clinicians often classify the hypothyroidism by two categories as primary hypothyroidism and secondary hypothyroidism.
In primary hypothyroidism fault is primarily in the thyroid gland when for some reasons thyroid is failing to produce adequate amount of iodothyronines. Primary hypothyroidism can be due to either iodine deficiency in the food or for a foetus in maternal blood or for destruction of thyroid due to surgical removal or radioiodine therapy called Hasimoto's disease. In secondary hypothyroidism fault lies in the pituitary or hypothalamus. Poor amount of secretion of TSH or TRH is the cause of hypothyroidism. Secondary hypothyroidism is rare in case.
Hypothyroidism can also be classified according to the age of onset. When hypothyroidism is present since birth it is called as cretinism. When hypothyroidism appears after the attainment of adulthood it is adult hypothyroidism or myxoedema.
In India cretinism or primary hypothyroidism is particularly common in the Himalayan regions that are regions which are far away from the sea and food is generally iodine deficient. The maternal blood is iodine deficient then the foetal thyroid gets no iodine from the maternal blood. The foetal central nervous system requires thyroid hormone T3 for its growth.
The neonate is thus born with hypothyroid state but clinically there is no symptom or sign. Only estimation of blood TSH which can now a dayis done. This is now a day done in advanced countries. It reveals the hypothyroid state. Also the breast milk contains no iodine. It is important to remember that the treatment of neonatal hypothyroidism must be started as early as possible. If the treatment is delayed the central nervous system damage becomes irreversible. In advance countries where occasional cases of such congenial hypothyroidism are detected, treatment is started within two weeks of birth.
Where these neonatal hypothyroidism remains untreated the subjects ultimately becomes a cretin. In a fully developed cretin all kinds of growth are retarded. Thus mental, physical and sexual growth of the subject is impaired and the subject is idiot. Short statured because bone maturation is retarded. They may also become potbellied and have saliva dripping from their mouth all the time. With affected subject no secondary sex characters like sexual hairs or development of reproductive organs and sexual maturity develops.
In this condition hyaluronic acid-protein,chondroitin sulphate forms and deposited in the subcutaneous tissue which are mistakenly called myxematous tissues. Hence there is due to deposition an oedema called myxoedema. The oedema however is nonpitting.
In adult hypothyroidism there is fault of central nervous system function, slow thinking loss of memory, dulling of intelligence. Nonpitting oedema leads to puffing of face, lake etc. Severe symptoms are bradycardia, abnormality in metabolism, fall or BMR and high serum cholesterol. Change in sexual behaviour is also noted. With treatment signs or symptoms of myxoedema can be corrected.
In this condition there is excessive activity of T4 and T3. Common causes include Grave's disease, multinodular goitre, thyroiditis and others.
Clinically hyperthyroid states have signs or symptoms of different organ systems like CVS-tachycardia or palpitation; central nervous system-tremor, hyperreflexia, psychosis; reproductive-menstrual abnormality, loss of libido, infertility; excess calorie gaining etc. There is in addition enlarged thyroid or goitre in Grave's disease. There is in addition expothalamus.
This is the commonest cause of hyperthyroidism and is also called exophthalmic goitre. Clinical features have been given below.
Laboratory investigation reveals elevated levels of serumT3, T4 and low level of TSH. Cause of ethopathagenesis of Grave's disease is as follow.
In the B lymphocytes of patients of Graves disease after Robert James Graves an Irish physician, abnormalities develop. B lymphocytes produce a chemical called the corpus lutein or CL. If there is no fertilization the corpus luteum begins to regenerate on the ninth day of its formation and the degeneration is complete on the fourteenth day of its formation. If however, pregnancy develops the corpus luteum stays and continues to function.
In the corpus luteum the granulosa cells proliferate. They become yellow and now they are called lutein cells. Antrum becomes filled with blood. In between the lutein cells some cells called paraleutein cells are seen.
If no pregnancy occurs the corpus luteum regenerates to become corpus albicans. Many second stage follicles fail to become graafian follicle. They also degenerate to become atretic follicle.
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