Subacute Thyroiditis With Very Elevated Thyroglobulin Level in a Patient on Chronic Adalimumab Therapy

Background: Viral infections are a well-recognized cause of subacute thyroiditis (SAT), but other etiologies are occasionally seen. Here we present a case of SAT in a patient receiving chronic tumor necrosis factor inhibitor (TNF-i) therapy. Serum thyroglobulin (Tg) levels in healthy individuals have been reported and range 1.40-29.2ng/mL in males and 1.50-38.5ng/mL. There are no known serum Tg levels of reference in SAT. Clinical Case: A 43-year-old woman with a history of psoriasis treated with adalimumab presented to her primary care physician (PCP) 2 months after her mother had noticed the patient’s new goiter. Patient recalled upper respiratory infection symptoms lasting 1.5 weeks, and subsequent agitation, insomnia, and a low-grade fever preceding the development of goiter. She denied neck compressive symptoms aside from mild dysphagia. She has been treated with adalimumab 40mg subcutaneous injection weekly for psoriasis with good results for the past 3.5 years and was on norethindrone 0.35mg daily for contraception. Her thyroid exam with her PCP revealed a diffuse painless goiter and she was clinically euthyroid. Labs revealed a TSH 1.44mIU/L [0.45-5.33], TT3 104ng/dL [60-181], fT3 3.3pg/mL [2.3-4.2], fT4 0.83ng/dL [0.89-1.76], and Tg 288.7ng/mL [1.6-50]. Thyroid antibodies (Tg, thyroid peroxidase and thyroid stimulating immunoglobulin) were negative. She tested negative for COVID-19. The neck ultrasound showed an enlarged pseudonodular thyroid gland with a heterogenous parenchyma and diffuse hypervascularity bilaterally (right lobe, 7.4 x 2.8 x 3.0 cm; left lobe, 8.4 x 3.2 x 3.6 cm; isthmus, 9 mm). A month later, repeat labs showed TSH 1.56 mIU/L, TT3 85 ng/dL, fT4 0.74 ng/dL, and Tg 231.2 ng/mL. She was subsequently referred to Endocrine Clinic 4 months after her initial presentation. She had a persistent diffuse painless goiter, minimally decreased in size, and she remained clinically euthyroid. Labs included a TSH 1.75 mIU/L and fT4 0.78 ng/dL. Conclusion: There are known associations of SAT with chronic TNF-i therapy in patients with psoriasis. Viral infections are an identified cause, but other triggers in chronic TNF-i therapy may exist. Serum Tg is elevated during SAT, but in this case Tg elevation was very significant. Although normal serum Tg levels are established in healthy individuals, there are no known reference values during SAT. Tg levels should not be used in acute illness period to evaluate illness severity or the resolution of SAT.