IgG4 immunohistochemistry in Riedel's thyroiditis and the recommended criteria for diagnosis: A case series and literature review

[The clinical case of IgG4-related thyroid disease in a 6-year-old child]

IgG4-related disease is a rare chronic pathology manifested by lymphoplasmacytic infiltration of one or more organs, the formation of storiform fibrosis, tissue edema, and an increase of IgG4 in the blood. This disease was singled out as an independent nosological unit only in 2001. The incidence is less than 1 in 100,000 people per year. Almost any organ can be affected in IgG4-related disease. The association of Riedel's thyroiditis with IgG4 was established in 2010. Riedel's thyroiditis is an extremely rare inflammatory disease of the thyroid gland, which diagnosis is complicated by an atypical course and the absence of characteristic symptoms. Less than 300 clinical cases of the disease have been described in the world, only two from them were in children. This article presents a clinical case of a 6-year-old boy with Riedel's thyroiditis.

Reshaping the Concept of Riedel's Thyroiditis into the Larger Frame of IgG4-Related Disease (Spectrum of IgG4-Related Thyroid Disease)

Recently, Riedel's thyroiditis (RT) was assimilated into the larger spectrum of immunoglobulin IgG4-related disease (IgG4-RD) in addition to a particular frame of IgG4-related thyroid disease (IgG4-RTD), underlying IgG4-RT, IgG4-associated Hashimoto's thyroiditis (and its fibrotic variant), and IgG4-related Graves's disease. Our objective was to overview recent data on RT, particularly IgG4-RD and IgG4-RTD. The case and study- sample analysis (2019-2023) included 293 articles and selected 18 original studies: nine single case reports (N = 9, female/male = 2/1, aged: 34-79 years, 5/9 patients with serum IgG4 available data, 2/5 with high serum IgG4) and four case series (N = 21; 4/5 series provided data on IgG4 profile, 3/21 had serum IgG4 assays, and 2/3 had abnormally high values). IgG4-RD and thyroid findings were analyzed in three cohorts (N = 25). Another two studies (N = 11) specifically addressed IgG4-RTD components. On presentation, the patients may have hypothyroidism, transitory thyrotoxicosis, goiter, long-term history of positive anti-thyroid antibodies, and hypoechoic ultrasound thyroid pattern. The 5-year analysis (N = 66) showed the rate of serum IgG4 evaluation remained low; normal values do not exclude RT. Mandatory histological and immunohistochemistry reports point out a high content of IgG4-carrying plasma cells and IgG4/IgG ratio. Unless clinically evident, histological confirmation provides a prompt indication of starting corticoid therapy since this is the first-line option. Surgery, if feasible, is selective (non-responders to medical therapy, emergency tracheal intervention, and open/core needle biopsy). Current open issues are identifying the role of serum IgG4 assays in patients with IgG4-RD, finding out if all cases of RT are IgG4-mediated, applying IgG4-RTD criteria of differentiation among four entities, and providing an RT/IgG4-RTD guideline from diagnosis to therapy. It remains that the central aim of approaching RT in daily practice is the early index of suspicion in order to select patients referred for further procedures that provide enough histological/immunohistochemistry material to confirm RT and its high IgG4 burden.

Immunoglobulin G4-Related Thyroid Disease: A Single-Center Experience and Literature Review

BACKGROUND

Immunoglobulin G4 (IgG4)-related disease is an entity that can involve the thyroid gland. The spectrum of IgG4-related thyroid disease (IgG4-RTD) includes Hashimoto thyroiditis (HT) and its fibrotic variant, Riedel thyroiditis, as well as Graves' disease. The early diagnosis of IgG4-RTD is important because it is a medically treatable disease, and a delay in the diagnosis might result in unnecessary surgery. We present a case series of IgG4-RTD with a review of the literature.

METHODS

We retrospectively reviewed the clinical presentation and the radiological and pathological findings of patients diagnosed with IgG4-RTD between 2017 and 2021 at a tertiary medical center in Korea. We also conducted a literature review of IgG4-RTD.

RESULTS

Five patients were diagnosed with IgG4-RTD during the study period. The patients' age ranged from 31 to 76 years, and three patients were men. Most patients visited the clinic for a neck mass, and hypoechogenic nodular lesions were observed on neck ultrasonography. Three patients had IgG4 HT, and two patients had IgG4 Riedel thyroiditis. All patients developed hypothyroidism that necessitated L-thyroxine replacement. The diagnosis of IgG4-RTD was confirmed after a pathological examination of the surgical specimen in the first two cases. However, the early diagnosis was possible after a core needle biopsy in three clinically suspected patients.

CONCLUSION

The diagnosis of IgG4-RTD requires clinical suspicion combined with serology and histological analyses using IgG4 immunostaining. The early diagnosis of IgG4-RTD is difficult; thus, biopsy with IgG4 immunostaining and serum IgG4 measurements will help diagnose patients suspected of having IgG4-RTD.