Autonomy of the thyroid gland: is there an "organ hyperthyroidism" of "euthyroid" patients?

Abstract

Classic thyrotoxicosis is defined as the clinical syndrome of hypermetabolism that results when concentrations of serum free thyroxine (fT4), serum free triiodothyronine (fT3), or both are increased and serum level of TSH is suppressed. The term of subclinical thyrotoxicosis refers to a usually asymptomatic state associated with normal serum fT4 and fT3 and low serum TSH concentrations. We describe a new entity of thyrotoxicosis under the term of "organ-selective thyrotoxicosis". This refers to patients with mild clinical symptoms of thyrotoxicosis and with a non-suppressible thyroid toxic adenomas and normal serum concentrations of fT4, fT3 and TSH. We compared symptoms and clinical signs of thyrotoxicosis with serum levels of fT4, fT3 and TSH in 33 patients with toxic adenomas. These patients were divided into 2 groups, 19 patients had normal concentrations of serum fT3, fT4 and TSH belonging to the group of "organ-selective thyrotoxicosis", 14 patients with subclinical thyrotoxicosis were in the control group. In both groups, mild symptoms of thyrotoxicosis were apparent but there was no significant difference between the 2 groups detectable. Therapeutic options were discussed with the patients referring to their symptoms. We describe 1 case of a female patient, in which we carried out an alcohol obliteration of a single toxic adenoma. Biological availability of thyroid hormones in patients with toxic adenomas might be elevated in selected organs although serum levels of fT4, fT3 and TSH are normal. This might be due to an increased production rate of T4 on the one hand and a specific peripheral T4/T3 conversion rate on the other hand. This might lead to an organ-selective thyrotoxicosis in the periphery without concerning the thyrotroph, so that TSH stays within the normal range. Necessity of therapeutic interventions depends on clinical signs and symptoms.