IgG4-associated sclerosing thyroiditis: one case, two different clinical courses
Authors: Korkmaz Fatma Nur , Canpolat Asena Gökçay , Ceyhan Koray 
Published: January 2023

Abstract
IgG4 related Diseases (IgG4- RD) are characterized swelling of affected organs, elevated levels of serum IgG4, dense lymphocyte infiltration and IgG4- positive plasma cells in tissues pathologically in the involved organs. Involvement of major organs is common and IgG4-RD may lead to organ failure, particularly in the pancreas, liver and biliary tree, kidneys, thyroid gland. We present a case of changing between subtypes of IgG4-related thyroid disease—transition from GD to IgG4-related sclerosing thyroiditis for the first time in the literature.
A 48-year-old female patient, who had a diagnosis of psoriasis, and asthma, was admitted to the hospital due to fatigue complaint in 9/2012. Her laboratory assessment was compatible with thyrotoxicosis. It was detected patchy hypoechoic areas within the gland and Vitti 3 blood in the parenchyma in the thyroid doppler ultrasonography (USG). The results were compatible with Graves disease (GD) and methimazole (MMI) and beta blocker treatment were started at diagnosis. Rapid changes in serum thyroid function tests (TFT) in 1–3 months of follow-up were observed under MMI treatment. The patient first described a pressure during swelling in her throat in 8/2016. Grade 3 goiter was detected in her physical examination (PE). The patient had unstable TFT and received short term-intermittent MMI treatment according to TFT results until 9/19. MMI was discontinued upon detection of TSH 29.18(0.38–5.33) µIU/mL. After approximately six months of euthyroid follow-up, she was admitted to the outpatient clinic with complaints of hypothyroidism and compression due to grade 2 goiter. The thyroid is hard on PE. Her laboratory assessments were compatible with hypothyroidism and levothyroxine (LT4) treatment was started. The thyroid volume was 38 ml, the parenchyma was markedly echogenic, no compression sign in adjacent structures on USG. Thyroid tru-cut biopsy was planned with the preliminary diagnosis of Riedel/ IgG4 related disease. Histopathological diagnosis on tru-cut biopsy of thyroid was fibrosclerosing chronic thyroiditis with severe collagen fibrosis and interstitial lymphocyte infiltration. The presence of IgG4 positive plasma cells in the fibrotic stroma was remarkable and compatible with IgG4-associated sclerosing thyroiditis (Figure 1). The serum Ig G4 level was detected as 1.27 g/L(0.04–0.86). No sign of fibrosing disease was detected in neck, thorax and abdomen imaging. The results of laboratory and autoantibody levels are summarized in Table 1 and the Figure 2 and 3.
Figure 1. Cytopathological evaluation A. Thyroiditis with diffuse collagen fibrosis and interstitial lymphoplasmacytic cell infiltration (chronic thyroiditis in the sclerosing/fibrotic stage). B. Fibroinflammatory reaction/chronic thyroiditis in core needle biopsy C. Immunohistochemistry: Intense IgG staining in interstitial lymphoplasmacytic cells, D. IgG4 positivity around 30% of IgG positive cells.
We present a patient who initially presented with thyrotoxicosis, which was controlled with short-term MMI therapy, then transitioned to hypothyroidism, and the final diagnosis was IgG4-induced thyroiditis. IgG4-related thyroiditis includes IgG4-related Hashimoto's thyroiditis (HT), Riedel's thyroiditis, fibrosing variant of HT, and GD with elevated IgG4 levels. The clinical course of these subtypes is not exactly known due to their rarity.