The disorder has three major manifestations:
Hyperthyroidism with diffuse goiter
The three manifestations need not appear together. Indeed one or two never appear, and moreover, the three may run courses that are largely independent of one another.
Graves' disease can occur at any age but is unusual before puberty. It most commonly affects the 30 to 50 year age group. The disease is more frequent in women, the ratio of predominance in women may be as high as 7 : 1. Genetic factors play a role. There is an association between the disease and the genes HLA ( human leucocyte antigen) B8, -DRw3, -Bw36, -Bw46. Indeed, a 50% concordance is found between identical twins. This means that if one individual in an identical pair of twins is afflicted with Graves' disease, the likelihood of the other sibling coming down with Graves' is 50%.
Being an autoimmune disease, there is a clinical and immunologic overlap between Graves' disease and other diseases with prominent autoimmune features. These include Hashimoto's thyroiditis, pernicious anemia, systemic lupus erythematosus ( SLE), rheumatoid arthritis ( RA), insulin- dependent diabetes mellitus ( IDDM), and Addison's disease.
Thyroid hormones are important mediators of growth and differentiation. The absence of which leads to cretins in childhood. The hormones are also responsible for the regulation of the various metabolic pathways which are vital for life. They are necessary for the normal function of many organ systems. In the thyroid gland, multiple follicles make, store and release thyroid hormones into the surrounding capillaries. These little vessels then bring the hormones to the rest of the body where they are needed.
"Thyroid hormones" refers mainly to two hormones T3 and T4, which are single, amino acids containing iodine. They are produced via a complicated pathway requiring the presence of iodine. Another hormone called TSH ( thyroid stimulating hormone) which originates from a "master gland" also known as the pituitary gland in the brain, controls the production of thyroid hormones. TSH not only stimulates the thyroid gland to churn out more hormones. If in excess, can cause overwhelming cell growth and division to result in goiter.
Most T3 and T4 released into the bloodstream are bound to proteins. Only the "free" component is biologically active and it is this component which decides the manifestations of thyrotoxicosis. The hormones exert their effects mainly by binding to nuclear receptors in cells to affect expression of genes.
In the presence of excess T3 and T4, an increase in number as well as affinity of beta-adrenergic receptors in the heart is noted. These receptors facilitate the action of "fight, flight and fright" hormones ( epinephrine, norepinephrine) which are positively chronotropic ( beat faster) and inotropic ( pump harder) to the heart. This may then lead to cardiac failure in older patients.
In fact, mild hyperthyroidism may produce severe disability in patients with underlying heart disease. Hence, all patients with unexplained cardiac failure or atrial arrhythmias should be examined for thyrotoxicosis. Hyperthyroidism also increases the basal metabolic rate, heat production and oxygen consumption (calorigenic action) of many tissues. Body temperature increases slightly and the patient experiences intolerance to heat. Flushing and sweating are just compensatory mechanism in an attempt to...