Atypical Clinical Courses of Graves' Disease Confound Differential Diagnosis of Hyperthyroidism

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Background: This study examined the appropriateness of the current paradigm for differential diagnosis of painless thyroiditis and Graves' disease (GD) in patients with thyrotoxicosis. Methods: We retrospectively evaluated the clinical course of 343 consecutive patients with hyperthyroidism diagnosed by Tc-99m pertechnetate thyroid uptake (TcTU) testing at our hospital from January 2011 to December 2017. Results: Of the 263 patients with normal or high TcTU levels (≥1.0%), 255 (97%) had unequivocal GD and 5 had spontaneous remission GD or atypical GD. Of the 10 patients with low TcTU levels (<1.0% and ≥0.5%), 7 had GD, while others had subclinical GD, spontaneous remission GD with later relapse, and painless thyroiditis. Of those with very low TcTU levels (<0.5%), most had thyroiditis (painless thyroiditis, 33/67 [49%]; subacute thyroiditis, 29/67 [43%]), and some were positive for anti-TSH receptor antibodies. Conclusion: Given that atypical GD may confound the diagnosis of thyrotoxicosis, it is essential to follow the patient as a tentative diagnosis, whatever the diagnosis. This is the first report clearly demonstrating that so far there is no gold standard for the diagnosis of GD. It is therefore urgent to establish a consensus on the definition of GD so that the specificity and sensitivity of future diagnostic tests can be determined.