Autoimmune thyroid disease and thyroid function test fluctuations in patients with resistance to thyroid hormone.

The frequency of AITD in male RTHβ patients was significantly higher compared to unaffected relatives. More than 20% of RTHβ patients temporarily showed laboratory findings atypical of RTHβ during their follow-up, and patients with AITD and specific THRB mutations were prone to display such findings. Therefore, genetic testing should be performed even for patients with fluctuations in thyroid function test results to avoid misdiagnosis and inappropriate treatment.