Benign thyroid nodule with normal iodide trap and defective organification.

Cold thyroid nodules are generally due to impaired iodide uptake, while organification remains normal. In a case of a nodule appearing hot one hour after Tc99 m and cold 24 h after 131I-iodide, in vivo investigations showed that the trapping function was unimpaired and that the defect lay in organification. An early thyroid scan taken with 131I-iodide showed definite radioactivity in the nodule which was dischargeable by K perchlorate. This finding was confirmed by in vitro study of the tissue. Indirect evidence suggests that a defect was present in the H2O2 generating system rather than in peroxidase.