| A great number of different mechanisms may impair normal thyroid function, thyroid autoimmunity being the prevailing cause of thyroid failure. The general classification of hypothyroidism is depicted in table 1. Hypothyroidism may be congenital or acquired. Acquired hypothyroidism is subgrouped into primary (or peripheral) hypothyroidism caused by a failure, spontaneous or not, of the function of the thyroid itself and secondary (or central), due to a lack of TSH or of TSH activity or to a deficit in hypothalamic TRH. |
