Hypothyroidism is the result from any condition that leads to thyroid hormone deficiency. It can result from problems that involve the thyroid gland itself (primary hypothyroidism), and pituitary disorders (secondary hypothyroidism).
- Iodine deficiency
- Genetic mutations: Inactivating mutation in the sodium-iodide symporter (NIS); TSH resistance (a mutation in the G-protein of the TSH receptor); inactivating mutation of the thyroid peroxidase enzyme (TPO)
- Decreased TSH secretion from the pituitary (secondary hypothyroidism). This can be due to an inactivating mutation of the TRH-receptor on the pituitary TSH cell.
- Autoimmune destruction of the thyroid gland (e.g. autoantibodies against the thyroid peroxidase enzyme) including lymphocyte infiltration.
- Radiation damage to the thyroid gland
Symptoms of hypothyroidism are lethargy, cold-intolerance, cretinism in young children, and myxedema (subcutaneous swelling, dry skin, hair loss, low body temperature, muscle weakness and slowed reflexes). Thyroxine therapy is used to treat hypothyroidism.
I. In most cases hypothyroidism requires life long thyroxine therapy.
II. Deficiency of thyroid hormone in infancy can cause growth retardation.
Extra info: Hypothyroidism caused by autoimmune destruction, or destruction due to inflammation always requires life long thyroxine therapy. In infancy, thyroxine is involved in development and growth of the CNS and various metabolic processes.