Radionuclide evaluation of thyroid disease in children

Abstract

A diagnosis of thyroid disease in children may be made with tests for thyroid hormone levels in blood samples (serum total thyroixine (T4), serum triiodotyronine (T3) resin test), and tests based on the peripheral action of thyroid hormone (bone age and form, growth characteristics, IQ, and EKG) together with other investigations such as antithyroid antibodies. This approach should be carried out before performing more sophisticated studies such as measurement of serum thyroid-stimulating hormone (TSH) levels, serum free thyroxine, serum T3, and TBG capacity for T4. Tests based on the administration of radionuclides to young patients are indicated when the primary diagnosis cannot be established by in vitro studies. In addition, radionuclide investigations may be indicated to identify the underlying thyroid pathology. These aspects of thyroid tests are discussed in detail. The author recommends using doses of 131 I from 5 to 20 μCi intravenously when simple in vivo investigations in selected cases are planned, and some detail is given as a guide to the investigation, particularly of agoitrous and goitrous hypothyroid children with 131 I. In the differential diagnosis of the various types of dyshormonogenesis, special procedures such as radiochromatography of thyroid tissue, when available, sera, and urine are indicated. Tests having these techniques as their basis are described. Other measurements such as the serum TSH response to thyroid-releasing hormone, the blood hormone response to TSH, and the urinary excretion of thyroid hormones are mentioned but they are not yet established as routine procedures in pediatric practice.