Na+, K+ ATPase activity in red cells predicts the recurrence of hyperthyroidism in patients with Graves' disease

Graves' disease is an autoimmune disorder characterized by a course of remission and relapse. Several parameters have been evaluated for their abilities to predict the clinical course of Graves' disease in patients treated with antithyroid drugs. We recently demonstrated in patients with hyperthyroidism dependent by Graves' disease, an impaired Na+, K+ ATPase activity in red cells and a correlation between ATPase and free T3. With the aim to clarify the relationship between the course of hyperthyroidism and the Na+, K+ ATPase activity during and after discontinuing the antithyroid therapy, we followed up 24 patients for two years. In our previous work by restoring a normal level of free T3, we obtained a normalization of Na+, K+ ATPase activity in the red cells of all the patients. However, in eight subjects after a period of 150 days following the suspension of therapy, we observed a new reduction of ATPase activity in a clinical condition of euthyroidism. The same subjects, newly evaluated after 150 days, developed a clinical and biochemical relapse of hyperthyroidism. We believe that the determination of Na+, K+ ATPase activity is able to predict the recurrence of hyperthyroidism in patients with Graves' disease.