The Wolff-Chaikoff Effect: Hypothyroidism due to Iodine Application

To the Editor. —  We read with interest the article by Johnson and Rapini in a recent issue of the Archives¹ on transient primary hypothyroidism induced by iodine application in an elderly woman.In a study on screening for hypothyroidism in Hamburg, West Germany, in a series of 91509 neonates, the determination of thyrotropin levels was done by the radioimmunologic thyrotropin neonatal dry spot test (Becton Dickinson & Co, Mountain View, Calif). Calibration of standards was performed on the basis of the international World Health Organization reference preparation hTSH MRC 68/38 (National Institute for Biological Standards and Control, London, England).In this series, the following data were obtained from nine of the 5-day-old neonates.

1. Initially, thyrotropin values were elevated and serum thyroxine values decreased below the lower limit for neonates (<77 nmol/L). Thus, these cases fulfilled the criteria for connatal hypothyroidism.^2,3

2. After the start of thyroxine therapy,