Autoimmune Thyroid Disorders in Autoimmune Addison Disease

Abstract

Context: Autoimmune thyroid disease is the most common endocrine comorbidity in autoimmune Addison disease (AAD), but detailed investigations of prevalence and clinical course are lacking.

Objective: This work aimed to provide comprehensive epidemiological and clinical data on autoimmune thyroid disorders in AAD.

Methods: A nationwide registry-based study including 442 patients with AAD and autoimmune thyroid disease were identified through the Norwegian National Registry of Autoimmune Diseases.

Results: Of 912 registered AAD patients, 442 (48%) were diagnosed with autoimmune thyroid disease. A total of 380 (42%) had autoimmune hypothyroidism. Of the 203 with available thyroid function tests at time of 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 the 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.

Keywords: Graves disease; autoimmune Addison disease; autoimmune hypothyroidism; autoimmune polyendocrine syndromes.

Figure 1.

Flowchart of the Autoimmune Addison Disease (AAD) cohort. Flowchart of the inclusion and exclusion criteria of patients from the Norwegian Registry of Organ-specific Autoimmune Diseases (ROAS).

Figure 2.

Onset of thyroid disorder. A, Bar chart illustrating the temporal relationship between onset of autoimmune Addison disease (AAD) and hypothyroidism in 361 of 380 patients. Year of diagnosis on the X axis. 0 is defined as simultaneous onset (diagnosis within same year) of AAD and hypothyroidism. For 19 patients, year of diagnosis was missing. B, Bar chart illustrating the temporal relationship between onset of AAD and hyperthyroidism in 76 of 78 patients. Year of diagnosis on the X axis. 0 is defined as simultaneous onset (diagnosis within same year) of AAD and hyperthyroidism. For 2 patients, year of diagnosis was missing.

Figure 3.

Diagnosis of autoimmune hypothyroidism. The number and percentages of patients with thyroid hormone levels in the normal range, subclinical hypothyroidism, and overt hypothyroidism at diagnosis in 203 of 380 autoimmune Addison disease patients.