Thyroid hormone resistance.

Abstract

Thyroid hormone resistance (THR) is a rare syndrome of reduced end organ sensitivity. Patients with THR have elevated serum free thyroxine (FT4), free triiodothyronine (FT3), but normal or slightly elevated serum thyrotropin values. The characteristic clinical feature is goitre without symptoms and metabolic consequences of thyroid hormone excess. THR can be classified on the basis of tissue resistance into pituitary, peripheral or generalised (both pituitary and peripheral) types. Mutations in the TRbeta gene, cell membrane transporter and genes controlling intracellular metabolism of thyroid hormone have been implicated. THR is differentiated from thyroid stimulating hormone (TSH) secreting pituitary adenoma by history of THR in the family. No specific treatment is often required for THR; patients with features of hypo- or hyperthyroidism are appropriately treated with levo-triiodothyronine (L-T3), levo-thyroxine (L-T4), dextro-thyroxine(D-T4) or 3,3,5 triiodo-thyroacetic acid (TRIAC). The diagnosis helps in appropriate genetic counselling of the family.