Hashimoto’s disease also known as Hashimoto’s thyroiditis is an autoimmune disease caused due to the defected immune system. In which disease the immune system attacks the self-tissue, thyroid gland, leading to its destruction.
Hashimoto’s thyroiditis is caused by the inflammation of the thyroid gland, in which the body acts on thyroid tissue as it is perceived as a foreign body
What is the Cause of Hashimoto’s Disease?
The Etiopathogenesis of Hashimoto’s disease is thought to be due to the combined effect of genetic and environmental factors, which favors the development of the disease. As it is an autoimmune disease, antithyroid antibodies are produced against the thyroid tissue. These antithyroid antibodies then attack the thyroid tissue and cause the destruction of the thyroid gland leading to impaired function of the same. There are several risk factors associated with the Hashimoto’s disease which include
- A positive family history.
- It is also associated frequently with other autoimmune diseases. It can be diagnosed simply by low plasma level of T3 and T4 hormone.
- The anti-thyroid antibody can also be detected.
- The age group affected by the disease is between 30 to 50 years of life and also it is pretty more common in females than males.
Risk Factors Associated with Hashimoto’s Disease
There is strong evidence in support of the genetic relation of the disease. Many monozygotic twins’ studies have revealed strong genetic component in the development of the disease with high concurrence rate. Positive family history of thyroid disease is pretty common with certain human leukocyte antigen/HLA genes.
Presence of any other autoimmune disease is also a risk factor for the development of the Hashimoto’s disease. Certain factors like environmental ones also play a role, such as high iodine in the diet, low concentration of some metals like Selenium in the body, some toxic drugs and other diseases have been incriminated for the development of autoimmune diseases of thyroid in a genetically predisposed person.
There is evidence for the incrimination of genes in the development of autoimmune thyroid disease in different ethnic groups residing in different geographical regions. The incidence of development of autoimmune thyroid disease in individual suffering from some genetic disorder like Turner syndrome, Down syndrome, Klinefelter syndrome is increased and is usually associated with antithyroid antibodies directed against thyroid tissue. The cytotoxic immune response of the body causes the depletion of thyroid tissue and impairing of the normal functioning of the same thus causing the decreased plasma level of T3 and T4 leading to the higher degree of primary hypothyroidism and the compensatory rise in the TSH level.
There is various mechanics system for the development of the thyroid disease. Various antibodies are present against thyroid tissue. Cytotoxic T cells activation as a response to cell-mediated immune response accompanied by T helper cells is the main pathway for the destruction of the thyroid tissue. With activation of T helper lymphocytes, macrophages also are involved which release inflammatory cytokines in the thyroid tissue causing more and more recruitment of macrophages inside thyroid.
Grossly the thyroid becomes enlarged and there is focal nodular appearance. Histologically parenchyma is infiltrated by various lymphocytes. There atrophic changes in the thyroid parenchyma, which during the course of disease get fibrosed end seen as a dense fibrotic band of collagen.
Recent studies have identified 5 stages of the progression of the disease as-
Genetic Predisposition- It is the initial stage of the disease where the person has a genetic predisposition, but have not been exposed to the risk factors so the levels of T3 and T4 in some individuals is normal and no anti-thyroid antibodies are seen.
Infiltration of Immune Cell in the Parenchyma of Thyroid- In this stage the thyroid is infiltrated by lymphocytes, which causes the destruction of the normal parenchyma. This stage is long and may take years to get a detected before much damage is done.
Subclinical Hypothyroidism- This stage is characterized by slightly elevated TSH level. There is increase in the concentration of anti-thyroid antibodies as compared to 2nd stage.
Overt Hypothyroidism- Here the destruction of the thyroid parenchyma is such that the normal function of that gland cannot be performed so there is decreased level of T3 and T4 and elevation in TSH level.
Progression to Other Autoimmune Diseases- As there is a loss of balance in the immune system of the body, the immune system may find another gland and to attract tissue.
The disease is more common in regions having high iodine intake and it can occur in all age groups, but is quite more common in between 30 and 50 years of age. The incidence of the disease is more in females than that of males and is strongly linked with hypothyroidism.