Clinical value of functional thyrotropin receptor antibodies in Serbian patients with Graves' orbitopathy

Controversies Surrounding IGF-I Receptor Involvement in Thyroid-Associated Ophthalmopathy

Background: Thyroid-associated ophthalmopathy (TAO, aka thyroid eye disease [TED], Graves' orbitopathy) remains poorly understood and inadequately treated since its initial description. It is disfiguring, can threaten vision, and represents an autoimmune process closely associated with thyroid disease. Unambiguous connections linking TAO to the glandular maladies of Graves' disease (GD) remain incompletely clarified. Detecting the thyrotropin receptor (TSHR) in periocular tissues suggests that this cell-surface protein represents a shared autoantigen with the thyroid gland, but we now know that its expression is ubiquitous. Most patients with TAO have relatively high circulating levels of activating anti-TSHR autoantibodies. Emerging more recently is the importance of insulin-like growth factor I receptor (IGF-IR) in the pathogenesis of TAO. The TSHR/IGF-IR signaling complex apparently drives circulating fibrocytes and the unique phenotypes of fibroblasts inhabiting the TAO orbit (GD-OF). Methods: The PubMed database was scanned for articles dating back to the earliest time periods covered. Keywords used for primary searches included thyroid-associated ophthalmopathy, Graves' orbitopathy, TED, orbit, TSH receptor, IGF-I receptor, and autoimmune thyroid disease. Secondary searches used numerous other search terms. Results: GD-OF have been characterized extensively as being particularly responsive to the immunological factors and key effectors in TAO pathogenesis. Both TSHR and IGF-IR are overexpressed by GD-OF and CD34+ fibrocytes and form a signaling complex. They are activated through this TSHR/IGF-IR complex to produce large amounts of hyaluronan and express multiple cytokines. This complex mediates cellular responses to pathogenic IgGs in TAO. CD34+ fibrocytes and CD34+ OF also express relatively high levels of multiple thyroid autoantigens. Identifying IGF-IR as a key component of a receptor complex and its intertwining signaling activities with those of TSHR has led to a targeted medical therapy for TAO. This therapy involves the selective systemic inhibition of IGF-IR. Conclusions: Much has been learned over the preceding decades about the pathogenesis of TAO. Among these is the identification of IGF-IR as a pivotal component underpinning the disease. This has led directly to development of an effective targeted therapy. Important gaps in our understanding persist, and current therapies have limitations. Thus, despite these advancements, considerably more remains to be achieved.

Clinical performance of a novel and rapid bioassay for detection of thyroid-stimulating immunoglobulins in Graves' orbitopathy patients: a comparison with two commonly used immunoassays

Background

For the selective detection of thyroid-stimulating hormone receptor antibodies with stimulating properties (thyroid-stimulating immunoglobulins; TSI), a novel and rapid bioassay (Turbo TSI) has been introduced. We evaluate the clinical performance of Turbo TSI in Graves' orbitopathy (GO) patients and compare it to a bridge-based TSI binding immunoassay and third generation TSH-R-binding inhibitory immunoglobulins (TBII) assay. Also, we investigate the association of Turbo TSI and TBII measurements with GO activity and severity, as well as response to intravenous methylprednisolone (IVMP), and compare results to previous findings on the bridge-based TSI binding immunoassay.

Methods

Turbo TSI, TBII and bridge-based TSI binding immunoassay measurements were performed in biobank serum from 111 GO patients and control cases (healthy controls [HC; n=47], primary Sjögren's disease [SD; n=10], systemic sclerosis [SSc; n= 10], systemic lupus erythematosus [SLE; n=10]). Clinical characteristics and response to treatment were retrospectively retrieved from GO patient files.

Results

Turbo TSI had the highest sensitivity (97.3%) and negative predictive value (96.1%), while bridge-based TSI binding immunoassay showed the highest specificity (100%) and positive predictive value (100%). Differentiating GO patients from control cases, receiver operating characteristic (ROC) analysis showed an area under the curve (AUC) of 98.5%, 95.7% and 99.8% for Turbo TSI, TBII and bridge-based TSI binding immunoassay, respectively. Turbo TSI (p<0.001) and TBII (p<0.01) levels were higher in patients with active compared to inactive GO. Correlation with CAS was stronger for Turbo TSI (r=0.42) than TBII (r=0.25). No statistically significant differences were observed in IVMP responders vs. non-responders for Turbo TSI (p=0.092) and TBII (p=0.21). For identifying active GO, an AUC of 75% with Turbo TSI and 67% with TBII was found. For IVMP response, AUC was 66.3% with Turbo TSI and 62.1% with TBII. In multivariate logistic regression analyses, both assays were independently associated with disease activity (p<0.01 for both assays) and IVMP response (p<0.01 for Turbo TSI; p<0.05 for TBII).

Conclusions

The new Turbo TSI functional bioassay has good clinical performance. Although turbo TSI is a stronger marker of activity and IVMP response than TBII, results are comparable to our previously published findings on the bridge-based TSI binding immunoassay.

Thyroid stimulating receptor autoantibodies

Thyroid-stimulating hormone receptor autoantibodies (TRAbs) play a crucial role as pathogenic antibodies in both the diagnosis and management of Graves' disease (GD). GD, an autoimmune disease resulting from a combination of genetic and environmental factors, is the most common cause of hyperthyroidism. With advancements in technology for TRAb detection and the availability of automated commercial kits, TRAb has become an essential clinical laboratory marker for the diagnosis of GD, as well as extra-thyroidal manifestations like Graves' ophthalmopathy (GO). This article provides a comprehensive review of TRAb, encompassing its clinical assays along with its significance in the clinical setting.

Redox mechanisms in autoimmune thyroid eye disease

Thyroid eye disease (TED) is an autoimmune condition affecting the orbit and the eye with its adnexa, often occurring as an extrathyroidal complication of Graves' disease (GD). Orbital inflammatory infiltration and the stimulation of orbital fibroblasts, triggering de novo adipogenesis, an overproduction of hyaluronan, myofibroblast differentiation, and eventual tissue fibrosis are hallmarks of the disease. Notably, several redox signaling pathways have been shown to intensify inflammation and to promote adipogenesis, myofibroblast differentiation, and fibrogenesis by upregulating potent cytokines, such as interleukin (IL)-1β, IL-6, and transforming growth factor (TGF)-β. While existing treatment options can manage symptoms and potentially halt disease progression, they come with drawbacks such as relapses, side effects, and chronic adverse effects on the optic nerve. Currently, several studies shed light on the pathogenetic contributions of emerging factors within immunological cascades and chronic oxidative stress. This review article provides an overview on the latest advancements in understanding the pathophysiology of TED, with a special focus of the interplay between oxidative stress, immunological mechanisms and environmental factors. Furthermore, cutting-edge therapeutic approaches targeting redox mechanisms will be presented and discussed.

High Diagnostic Accuracy of Thyroid-Stimulating Hormone (TSH) Receptor Antibodies in Distinguishing Graves' Disease and Subacute Thyrotoxicosis in the Indian Population

BACKGROUND AND OBJECTIVE

Thyrotoxicosis is a common clinical condition encountered in endocrine practice. Graves' disease and subacute thyroiditis are the two common causes of thyrotoxicosis and often have overlapping clinical and biochemical features. 99mTc thyroid scintigraphy is the most commonly used confirmatory test to differentiate the two conditions but is not available in the majority of the second-tier cities of India. However, obtaining thyroid stimulating hormone (TSH) receptor antibodies (TSHrAb), another accurate test to differentiate the two conditions, in second-tier cities by outsourcing to labs in major cities is a feasible option nowadays. However, the data on the performance of TSHrAb to differentiate the two conditions in Indian patients is limited. Hence, we have evaluated the diagnostic accuracy of TSHrAb in the Indian population to differentiate Graves' disease and subacute thyroiditis.

MATERIALS AND METHODS

This prospective study was conducted on 115 consecutive newly diagnosed thyrotoxicosis patients presenting to the Department of Endocrinology at a tertiary health care centre in India. Clinical parameters like throat pain, duration of symptoms, and grade of goitre were noted. Measurement of total tri-iodothyronine (TT3), total thyroxine (TT4), TSH, TSHrAb, and 99mTc thyroid scintigraphy were performed in all participants. All participants were followed up at least for six months after the recruitment. Increased tracer uptake (>4%) and/or increased thyroid to parotid trace uptake ratio (>2.5) were used to diagnose Graves' disease.

RESULTS

Eighty-one and 34 patients were diagnosed with Graves' disease and subacute thyroiditis, respectively. TT3/TT4 ratio had low diagnostic accuracy (area under the curve (AUC): 0.6, best cut-off: 15.6, sensitivity: 53.1%, specificity: 79.4%). TSHrAb had the best AUC (0.9) to distinguish Graves' disease from subacute thyroiditis (cut-off: 2.0 IU/L, sensitivity: 97.5%, specificity: 100%). In contrast, the kit manufacturer's reference range (1.75 IU/L) was slightly more sensitive (98.8%), but less specific (94%).

CONCLUSION

The TT3/TT4 ratio is not a good test to differentiate Graves' disease and subacute thyroiditis. TSHrAb is accurate in distinguishing Graves' disease from subacute thyroiditis and a level of 2.0 may be a more accurate cut-off to differentiate the two conditions in the Indian population.

The phenotype of Graves' orbitopathy is associated with thyrotropin receptor antibody levels

PURPOSE

Graves' orbitopathy (GO) is a specific inflammatory disorder of the orbit characterized by a highly heterogeneous clinical phenotype. The role of thyrotropin receptor antibodies (TSH-R-Ab) has been widely researched, however there is still no evidence that these antibodies have a direct pathogenic role in this pathology. The aim of this study was to examine their relation to the individual clinical features of GO.

METHODS

Ninety-one consecutive patients with GO were recruited. Total antibody concentration (TSH-R binding inhibitory immunoglobulins, TBII) and their functional activity (stimulating TSH-R-Ab, TSAb) were measured using binding immunoassay and cell-based bioassay, respectively.

RESULTS

Both TSAb and TBII levels were significantly associated to the clinical parameters of GO activity. TSAb was a more sensitive serological marker compared to TBII pertaining to eyelid retraction and edema, proptosis, extra-orbital muscle disorders, diplopia, irritable eye symptoms, and photophobia. TSAb, but not TBII, was a significant predictive marker of conjunctival redness, chemosis, caruncle/plica inflammation, eye irritation, and orbital pain, (odds ratio: 3.096, p = 0.016; 5.833, p = 0.009; 6.443, p = 0.020; 3.167, p = 0.045; 2.893, p = 0.032; versus 2.187, p = 0.093; 2.775, p = 0.081; 3.824, p = 0.055; 0.952, p = 0.930; 2.226, p = 0.099, respectively). Neither TSAb nor TBII correlated with the level of proptosis (ρ = 0.259, p = 0.090, and ρ = 0.254, p = 0.104, respectively), however rising TSAb levels were strongly associated to the level of proptosis.

CONCLUSIONS

TSH-R-Ab were significantly associated with GO's phenotype. Especially TSAb, as a sensitive and predictive serological biomarker, can improve diagnosis and management of GO.

Anti-nuclear autoantibodies in Graves' disease and Graves' orbitopathy

OBJECTIVE

A relationship between thyroid and non-organ-specific autoimmunity could be relevant for Graves' orbitopathy (GO), which affects connective tissue. We investigated the association between GO and anti-nuclear antibodies (ANAs).

METHODS

Retrospective investigation was conducted in 265 patients with Graves' disease (GD), 158 with and 107 without GO. Primary outcome was: prevalence of ANAs in GO vs no-GO. Secondary outcomes were: (1) relationship between ANAs and GO features; (2) prevalence of ANAs in GD compared with non-autoimmune hyperthyroidism [(78 patients with toxic nodular goiter (TNG)]; (3) distribution of ANA patterns.

RESULTS

ANAs were detected in 212 (80%) GD patients, but prevalence did not differ between GO (79.7%) and no-GO (80.3%). Higher ANA titers (1:160) were more common in GO (51.5 vs 38.3%), but only nearly significantly (OR 0.5; 95% CI: 0.3-1; P = 0.059). Proptosis was lower in ANA-positive patients (mean difference: - 1.4 mm; 95% CI from - 2.5 to - 0.3; P = 0.011), in whom nearly significantly lower CAS (Mann-Whitney U: 1.5; P = 0.077) and eyelid aperture (mean difference: - 0.9 mm; 95% CI from - 2 to 0; P = 0.062) were observed. Prevalence of ANAs in GD was lower than in TNG (80 vs 91%; OR 0.3; 95% CI: 0.1-0.9; P = 0.028), but nuclear speckled pattern was more frequent (OR 22.9; 95% CI 1.3-381.3; P = 0.028).

CONCLUSIONS

Although ANAs are not more frequent in GO, they seem to exert a protective role on its severity and on development of GD. A switch of T cell population in ANA-positive patients, resulting in a different phenotype, may be responsible. Further studies are needed to investigate the mechanisms.

A review of TSHR- and IGF-1R-related pathogenesis and treatment of Graves' orbitopathy

Graves' orbitopathy (GO) is an organ-specific autoimmune disease, but its pathogenesis remains unclear. There are few review articles on GO research from the perspective of target cells and target antigens. A systematic search of PubMed was performed, focusing mainly on studies published after 2015 that involve the role of target cells, orbital fibroblasts (OFs) and orbital adipocytes (OAs), target antigens, thyrotropin receptor (TSHR) and insulin-like growth factor-1 receptor (IGF-1R), and their corresponding antibodies, TSHR antibodies (TRAbs) and IGF-1R antibodies (IGF-1R Abs), in GO pathogenesis and the potentially effective therapies that target TSHR and IGF-1R. Based on the results, OFs may be derived from bone marrow-derived CD34+ fibrocytes. In addition to CD34+ OFs, CD34- OFs are important in the pathogenesis of GO and may be involved in hyaluronan formation. CD34- OFs expressing Slit2 suppress the phenotype of CD34+ OFs. β-arrestin 1 can be involved in TSHR/IGF-1R crosstalk as a scaffold. Research on TRAbs has gradually shifted to TSAbs, TBAbs and the titre of TRAbs. However, the existence and role of IGF-1R Abs are still unknown and deserve further study. Basic and clinical trials of TSHR-inhibiting therapies are increasing, and TSHR is an expected therapeutic target. Teprotumumab has become the latest second-line treatment for GO. This review aims to effectively describe the pathogenesis of GO from the perspective of target cells and target antigens and provide ideas for its fundamental treatment.

Current concepts regarding Graves' orbitopathy

Graves' orbitopathy (GO) is an orbital autoimmune disorder and the main extrathyroidal manifestation of Graves' disease, the most common cause of hyperthyroidism. GO affects about 30% of Graves' patients, although fewer than 10% have severe forms requiring immunosuppressive treatments. Management of GO requires a multidisciplinary approach. Medical therapies for active moderate-to-severe forms of GO (traditionally, high-dose glucocorticoids) often provide unsatisfactory results, and subsequently surgeries are often needed to cure residual manifestations. The aim of this review is to provide an updated overview of current concepts regarding the epidemiology, pathogenesis, assessment, and treatment of GO, and to present emerging targeted therapies and therapeutic perspectives. Original articles, clinical trials, systematic reviews, and meta-analyses from 1980 to 2021 were searched using the following terms: Graves' disease, Graves' orbitopathy, thyroid eye disease, glucocorticoids, orbital radiotherapy, rituximab, cyclosporine, azathioprine, teprotumumab, TSH-receptor antibody, smoking, hyperthyroidism, hypothyroidism, thyroidectomy, radioactive iodine, and antithyroid drugs. Recent studies suggest a secular trend toward a milder phenotype of GO. Standardized assessment at a thyroid eye clinic allows for a better general management plan. Treatment of active moderate-to-severe forms of GO still relies in most cases on high-dose systemic-mainly intravenous-glucocorticoids as monotherapy or in combination with other therapies-such as mycophenolate, cyclosporine, azathioprine, or orbital radiotherapy-but novel biological agents-including teprotumumab, rituximab, and tocilizumab-have achieved encouraging results.

SENSITIVITY OF THREE THYROTROPIN RECEPTOR ANTIBODY ASSAYS IN THYROID-ASSOCIATED ORBITOPATHY

Background

Thyrotropin receptor autoantibodies (TSH-RAb) are indispensable biomarkers in the laboratory assessment of thyroid-associated orbitopathy (TAO). Clinical sensitivity of three different assays for TSH-R-Ab determination was evaluated in patients with TAO.

Methods

87 consecutive TAO patients were enrolled and their serum samples analyzed in parallel with three assays. An ECLIA competitive binding and a chemiluminescent bridge immunoassay were used to measure total and binding TSH-R-Ab concentration, while their functional activity was determined using a stimulatory TSH-R-Ab (TSAb) cellbased bioassay.

Results

Compared to the two binding assays (ECLIA p<0.001, bridge p=0.003), the TSAb bioassay was more sensitive pertaining to the positive detection of TSH-R-Ab in TAO patients. No difference (p=0.057) was noted between the ECLIA and bridge assays regarding sensitivity rate. All patients with active and/or moderate-to-severe TAO tested positive in the TSAb bioassay (100% and 100%, respectively), while the positivity rates for bridge and ECLIA binding assays were 89.7% and 82.1% for active TAO, and 90.2% and 86.3% for severe TAO, respectively. Negative predictive values of the bioassay, bridge, and ECLIA assays were 100%, 75%, and 71%, respectively for active TAO, and 100%, 86%, and 71%, respectively for moderate-to-severe TAO. The superiority of the bioassay was most prominent in euthyroid (ET) TAO. Positivity rates of the TSAb bioassay, bridge and ECLIA binding assays were 89.6%, 75%, and 64.6%, respectively for inactive TAO; 86.1%, 69.4%, and 52.8%, respectively for mild TAO; 87.5%, 62.5%, and 12.5%, respectively for euthyroid TAO. The bridge assay correlated better with the ECLIA binding assay (r=0.893, p<0.001), compared to the bioassay (r=0.669, p<0.001).

Conclusions

In patients with TAO of various activity and severity, the TSAb bioassay demonstrates a superior clinical performance compared to both ECLIA and bridge binding assays.