Endocrine Abstracts

The transition of hypothyroidism from Hashimoto’s thyroiditis into hyperthyroidism (Graves’ disease) is uncommon, and the underlying causes are still unknown. We studied clinical characteristics in patients with the conversion of preexisting Hashimoto’s thyroiditis to Graves’ disease compared to patients with Hashimoto’s thyroiditis or Graves’ disease alone.

Patients and Methods: Retrospective comparative case series of 42 patients (mean age 53 years, 95%-CI [47.9;58]) with preexisting hypothyroidism due to Hashimoto’s thyroiditis who developed hyperthyroidism (Graves’ disease with positive TSH receptor antibodies). Data were compared with 30 patients with Hashimoto’s thyroiditis (mean age 48.5 years, 95%-CI [44;53]) and 38 patients with Graves’ disease (mean age 48.5 years 95%-CI [44;53.9]). In all three groups, female patients were predominant (Female to male ratio case group 38:4, Hashimoto group 26:4 and Graves’ disease 36:2). Social data (age, sex, origin, marital status, number of children, residential environment, occupational status, stressful life events, smoking, and alcohol), clinical data (body mass index, concomitant diseases, concomitant medication, therapy for thyroid dysfunction) and biological data (TSH, freeT3, free T4 and thyroid antibodies) were analyzed.

Results: Hypothyroid patients were treated for a mean time of 12.2 years before they developed hyperthyroidism. The mean dose of levothyroxine to maintain euthyroidism was 92 micrograms per day. Before manifestation of hyperthyroidism, patients who converted to Graves’ disease showed significantly higher TSH values (Wilcox-test P=0.003) and significantly lower T4 values (Wilcox-test P=0.02) than patients with Hashimoto’s thyroiditis alone. Compared to patients with Hashimoto’s and Graves’ disease, conversion patients were significantly more likely to take concomitant medications. No significant difference was found in the social factors of patients with conversion compared with Hashimoto’s and Graves’ disease controls. Alcohol consumption and smoking status were comparable. No differences were seen in TSH, T3 and T4 levels in hyperthyroidism between conversion patients and patients with Graves’ disease and in the distribution of thyroid-specific antibodies between case and control patients.

Conclusion: Smaller case series have been published regarding patients with conversion from Hashimoto’s thyroiditis to Graves’ disease. So far, our study is the largest case series and the only one with a comparison of patients with Hashimoto’s thyroiditis or Graves’ disease alone. There was a significant difference in the TSH and T4 levels between conversion patients before manifestation of Graves’ disease and Hashimoto’s patients. No difference could be seen in the other clinical parameters. In the future, genetic and immunological studies may identify factors separating these disease entities better.