Uptake of Radioactive Iodine by the Normal and Disordered Thyroid Gland in Children

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Abstract
Studies of the uptake of radioactive iodine by the normal and hyperfunctioning thyroid gland in adults have been published by Hamilton and Soley, Hertz, Roberts and Salter, (1, 2) and others. Hamilton, Soley, Reilly, and Eichorn have reported on iodine studies in a small series of cases of childhood hypothyroidism, including some with goiter (3). Most of their tests were made with eight-day iodine containing an appreciable admixture of stable iodine; with such material the apparent uptake is always much less than with a “carrier-free” preparation in which all the iodine is radioactive. Since the search for an unambiguous indicator of thyroid function in children, particularly in infants, still continues, the present study was undertaken in the hope of achieving this goal. Eight-day radioactive iodine (I131), carrier-free, was obtained from the cyclotron laboratory of the Massachusetts Institute of Technology in dilute solution of sodium iodide. The amount of the latter was so small as to be considered physiologically negligible. The material was administered quantitatively by mouth, a stomach tube being used in the case of infants and uncooperative small children. The subjects were not fasted. The doses varied from 20 to 40 microcuries (containing not more than 2 micrograms of iodine) in about 20 c.c. of solution. Smaller amounts were given to babies than to older children, but they were not calculated accurately on a weight basis. The relative quantities of the iodine concentrated in the thyroid glands were determined by measurements with a shielded Geiger counter placed in a fixed position over the front of the neck. These were related to the administered doses by measurements in the laboratory with a “phantom” set-up approximating the geometrical relationships with the patient. Whenever possible, all urine was collected for two successive 24-hour periods for measurement of the amount of iodine excreted. Pathological cases were selected chiefly on the basis of medical interest; this resulted in the study of infants and children of from three weeks to fourteen years. To eliminate differences in uptake due to possible variations in the material received from the cyclotron, an effort was made to study a control child of the same age and of approximately the same size simultaneously with each patient. The controls all came from the hospital population. While none showed features which justified the suspicion of “glandular” disorder, no matter how vague, only a few were strictly well children. The majority were suffering from, or in convalescence after, various illnesses, such as infection, diarrhea, or nutritional disorder, which can certainly be conceived to have affected temporarily the state of activity of the thyroid gland. The precaution of studying a control at the same time as the patient proved unnecessary, since significant variations in the quality of the test material were not detected.