Early tissue distribution of therapeutic 131I in a patient with thyrotoxicosis.

A therapeutic dose of 131I was given to a 53-year-old man with thyrotoxicosis three and one-half hours prior to death. The distribution of 131I in the thyroid gland was studied by autoradiography, and the radioactivity in various fresh tissues was measured. Radioactivity was distributed evenly throughout the colloid; small amounts were present in follicular cells. Radioactivity was not localized to the periphery of colloid follicles as observed in an earlier report. Papillary projections were associated with increased radioactivity. Decreased radioactivity was associated with oxyphilic cells. Measurement of 131I in individual tissues showed that per gram of tissue the thyroid gland contained approximately 50 times that of intestine and spleen and approximately 100 times that of liver and bone.