A decreased level may be found in liver dysfunction, overactive thyroid (hyperthyroidism), malabsorption, malnutrition, or advanced cancer, among other conditions.
Hyperthyroidism is often associated with the body's production of autoantibodies in the blood which causes the thyroid to grow and secrete excess thyroid hormone.
Radiation. Radioactive iodine used to treat hyperthyroidism (overactive thyroid) or radiation treatments for head or neck cancers can destroy the thyroid gland.
Hyperthyroidism, whooping cough, chickenpox, measles, and Hib disease (a bacterial infection) may cause mental retardation if they are not treated adequately.
Although hypothyroidism usually develops gradually, when the disease results from surgery or other treatment for hyperthyroidism, symptoms may appear suddenly and include severe muscle cramps in the arms, legs, neck, shoulders, and back.
For example, cardiomyopathy is very often present in cases of undiagnosed feline hyperthyroidism in which the excess thyroid hormones cause the heart to work overtime, thus wreaking havoc on its function over a period of time.
Other names for hyperthyroidism, or specific diseases within the category, include Graves' disease, diffuse toxic goiter, Basedow's disease, Parry's disease, and thyrotoxicosis.
An elevated body temperature (basal body temperature) above 98.6°F (37°C) may be an indication of a heightened metabolic rate (basal metabolic rate) and hyperthyroidism.
Individuals with glaucoma, history of heart attack, arteriosclerosis, hyperthyroidism and high blood pressure should not take this diet drug.
Newborn screening and immediate treatment for PKU and hyperthyroidism can usually catch these disorders early enough to prevent retardation.