In the case of iodide deficiency, the thyroid becomes inordinantly large and is called a goiter . The most severe and devestating form of hypothyroidism is seen in young children with congenital thyroid deficiency. If that condition is not corrected by supplemental therapy soon after birth, the child will suffer from cretinism , a form of irreversible growth and mental retardation. Most cases of hypothyroidism are readily treated by oral administration of synthetic thyroid hormone. In times past, consumption of dessicated animal thyroid gland was used for the same purpose.
Hyperthyroidism results from secretion of thyroid hormones.
In most species, this condition is less common than hypothyroidism. In humans the most common form of hyperthyroidism is Graves disease , an immune disease in which autoantibodies bind to and activate the thyroid-stimulating hormone receptor, leading to continual stimulation of thyroid hormone synthesis. Another interesting, but rare cause of hyperthyroidism is so-called hamburger thyrotoxicosis . Common signs of hyperthyroidism are basically the opposite of those seen in hypothyroidism, and include nervousness, insomnia, high heart rate, eye disease and anxiety.