Proposed classification of congenital primary hypothyroidism

Screening newborns for congenital hypothyroidism (a condition of decreased activity of the thyroid gland, which is present at birth) can be performed to identify this condition. Early treatment may avoid the development of mental retardation. In 1987, recommended guidelines for newborn screening were established jointly by the American Academy of Pediatrics and the American Thyroid Association. At that time, an optional test was thyroid scintigraphy with technetium-123, a study of radioisotope uptake in specific body tissue. This test, although providing a more specific diagnosis, was not recommended for routine use because of a slight risk of radiation exposure. However, this position does not represent a maximum diagnostic effort, which should be made to obtain a specific diagnosis as early as possible, as the disease will require lifelong treatment. A classification of congenital primary hypothyroidism is proposed that clarifies the genetic and abnormal physiologic variations of this heterogeneous condition. The two main categories are dysgenetic hypothyroidism (abnormal thyroid gland formation), which includes athyrosis and ectopia (absence and abnormal location of the thyroid, respectively); and dysfunctional thyrotic hypothyroidism, which includes conditions of abnormal hormone production both with and without goiter, along with transient and undefined primary thyroid function abnormalities. Previously, it was thought that most cases of congenital hypothyroidism were due to anatomic malformation of the thyroid gland. However, increased use of scintigraphy has shown an increasing percentage of babies with hypothyroidism who have identifiable thyroid glands in the proper location. The category of dysfunctional thyrotic hypothyroidism is broad enough to include a variety of abnormalities that may be defined in the future. (Consumer Summary produced by Reliance Medical Information, Inc.)