An unusual case of graves' disease following subacute thyroiditis in a chinese man

The occurrence of Graves' disease (GD) after subacute thyroiditis (SAT) is rare, with only 34 cases, mostly middle-aged women, being described in the literature. Our patient is a 32-year-old Chinese man with no previous history of thyroid disease who developed typical SAT with anterior neck swelling and pain, sore throat, 14-pound weight loss, fever and mild hyperthyroidism (TSH 0.03 mIU/mL, FT4 2.40 ng/dl, and normal T3). Antibiotics were prescribed without improvement and testing for SARS CoV-2 RNA was negative. CRP and ESR were elevated (4.3mg/dl and 21 mm/hr respectively) and thyroid autoantibodies were negative at initial presentation. Glucocorticoid treatment for 6 weeks led to resolution of hyperthyroidism and symptoms. Three weeks after discontinuation of steroids, hyperthyroidism recurred (TSH <0.01 mIU/mL, T3 257 ng/dl and FT4 3.03 ng/dl) without neck tenderness and with normal repeat CRP and ESR (0.1mg/dl and 4mm/hr, respectively). Repeat thyroid autoantibodies were elevated (TSI 3.42 IU/L, TPO Ab 805 IU/mL, TRAB 8.72 IU/L), thyroid radioactive iodine uptake (RAIU) was elevated (66.2%), and thyroid scan showed diffuse homogeneous radiotracer uptake consistent with Graves' disease (GD). The patient had complete resolution of symptoms of hyperthyroidism and normalization of thyroid function (FT4 at 1.32 ng/dl and TT3 at 110 ng/dl) one month after starting methimazole. HLA testing revealed presence of HLA- B∗35 and -DRB1∗15:01 alleles which are associated with SAT and GD respectively;the latter allele has been found specifically in Chinese patients with GD. GD after SAT is rare in a young healthy man;this phenomenon has not been reported in a Chinese patient. This unusual change in diagnosis should be considered when symptoms and signs of hyperthyroidism do not resolve as expected or return after a period of improvement since management is dependent upon accurate diagnosis. Change from SAT to GD can be determined by new elevation of thyroid autoantibodies, change from elevated to normal ESR and CRP, and elevated RAIU. Testing for presence of HLA alleles revealed an underlying genetic predisposition to SAT and GD in our case.