Autoimmune Thyroid Disorders in Autoimmune Addison Disease

Context: Autoimmune thyroid disease is the most common endocrine co-morbidity in autoimmune Addison's disease (AAD), but detailed investigations of prevalence and clinical course is lacking. Objective: Provide comprehensive epidemiological and clinical data on autoimmune thyroid disorders in AAD. Design and patients: A nationwide registry-based study including 442 patients with AAD and autoimmune thyroid disease, identified through the Norwegian National Registry of Autoimmune Diseases. Results: Of 912 registered AAD patients, 442 (48%) were diagnosed with autoimmune thyroid disease. Three hundred and eighty (42%) had autoimmune hypothyroidism. Of the 302 with available thyroid function tests at time for diagnosis, 20% had overt hypothyroidism, 73% had subclinical hypothyroidism and 7% had thyroid levels in the normal range. Negative thyroid peroxidase antibodies was found in 32%. Ninety-eight percent were treated with levothyroxine, 5% with combination therapy with liothyronine or thyroid extracts, and 1% were observed without treatment. Seventy-eight patients (9%) were diagnosed with Graves' disease (GD), of whom 16 (21%) were diagnosed with autoimmune hypothyroidism either before onset or after remission of GD. At the end of follow-up 33% had normal thyroid hormone levels without antithyroid-drugs or levothyroxine treatment. The remaining had either active disease (5%), had undergone ablative treatment (41%), or had developed autoimmune hypothyroidism (21%). Conclusion: The true prevalence of hypothyroidism in AAD is lower than reported in current literature. Careful consideration of the indication to start thyroxin therapy is warranted. Long-term remission rates in GD patients with AAD are comparable to recent reports on long-term follow-up of patients without AAD.