[Hypothyroidism related to excess iodine]

WOLFF-CHAIKOFF'S EFFECT: The thyroid gland has a capacity to reduce thyroid hormone production in the presence of excess iodine by reducing the organification of the iodine. This Wolff-Chaikoff effect is observed after 48 hours and protects the organism from excessive synthesis of the thyroid hormones. This effect is usually temporary and within a few days thyroid hormone synthesis returns to normal through the so-called 'escape' phenomenon. However in a few normal individuals and in some susceptible patients, the escape does not occur. THE CONTEXT OF OCCURRENCE: Iodine-induced hypothyroidism is observed in fetuses, newborn, adults and in the elderly. It is observed in individuals without underlying overt thyroid disorder, and specially in patients with autoimmune thyroiditis or those previously treated for thyroid diseases (Graves' disease, subacute or pospartum thyroiditis, iatrogenic thyroid dysfunction...). FROM A CLINICAL AND PROGRESSIVE POINT OF VIEW: The hormone deficiency is of obvious clinical expression, or sometimes discreet and revealed by hormone exploration. It is usually temporary, regressing with a few days or weeks after iodine withdrawal. Nevertheless, some patients require transient hormone replacement therapy.