Funny thyroid function tests - TSHoma and post-COVID 19 thyroiditis leading to confusing thyroid function tests dynamics, a case report

ABSTRACT

Background: We present the case of a male patient with a diagnosis of TSH-secreting pituitary adenoma (TSHoma) who became infected with SARS-CoV-2 and developed a post-COVID-19 thyroiditis with resultant confusing changes in his thyroid function tests (TFTs). Case Presentation The patient presented with an incidental finding of elevated Free T4 and inappropriately normal TSH, confirmed on multiple analytical platforms. A TRH test showed a flat TSH response, and an MRI pituitary showed a 2.4 cm macroadenoma. Somatostatin analogue treatment was commenced pending surgery, with rapid normalization of TFTs. The patient then became symptomatic of headache, pyrexia, dysgeusia and anosmia lasting two weeks, at a time when the first wave of the COVID-19 pandemic was affecting Ireland. The patient had been a close contact of two confirmed COVID-19 cases. He did not have a SARS-CoV2 PCR test at the time but later tested positive for COVID-19 spike and nucleocapsid antigen IgG antibodies (vaccine naïve), indicating previous exposure to SARS-CoV-2. Two months after this illness, the patient’s TFTs showed a pattern typical of primary hyperthyroidism with grossly elevated FT4 and fully suppressed TSH (with co-existent thyrotoxicosis symptoms), followed by a pattern of primary hypothyroidism with a low FT4 and high TSH – a pattern consistent with subacute thyroiditis post-viral illness. TRAb was negative. The patient’s TFTs later showed high normal TSH and normal FT4 while continuing lanreotide therapy. He is currently euthyroid and awaiting pituitary surgery which was delayed due to the COVID-19 emergency. Conclusion: To our knowledge, this is the first case of post-COVID-19 thyroiditis in a patient with underlying TSHoma. The case highlights the importance of considering an alternative or new diagnosis in the setting of rapidly changing patterns in thyroid function tests, and for close clinical and biochemical follow-up in these situations. The patient gave written consent to this publication. SARS-CoV-2 = Severe Acute Respiratory Syndrome Coronavirus 2 TFT = Thyroid Function Test FT4 = Free Thyroxine TSH = Thyroid-Stimulating Hormone TRH = Thyrotropin-Releasing Hormone MRI = Magnetic Resonance Imaging TRAB = TSH Receptor Antibodies Anti-TPO Ab = Anti-Thyroid Peroxidase Antibodies