Detection of Thyroid-Stimulating Antibody in Patients with Inflammatory Thyrotoxicosis

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.

Utility of TSH Receptor Antibodies in the Differential Diagnosis of Hyperthyroidism in Clinical Practice

Graves' disease (GD) is the most common cause of hyperthyroidism in iodine-sufficient areas. It is important to distinguish GD from other causes of hyperthyroidism for optimal management. Thyroid stimulating hormone receptor antibody (TRAb) test is a commonly used test for this purpose. However, the sensitivity for this test in routine clinical practice may be affected by various factors leading to fallacies in diagnosis.

Materials and Methods

A retrospective study was performed to assess the utility of an automated electrochemiluminescence TRAb immunoassay (Roche) in differentiating GD from non-Graves' disease (NGD) in routine clinical practice.

Results

In 227 subjects, 146 had GD and 81 had NGD. Total T3, Total T4, Free T4, and TRAb were significantly higher in people with GD in comparison to NGD. The area under the receiver operating characteristics (ROC) curve for the assay was 0.96 (95% CI: 0.926 to 0.984, P < 0.0001). The optimal threshold for the test derived from the ROC was 3.37 IU/L, which is more than the cut-off of 1.75 IU/L suggested by the manufacturer. The sensitivity/specificity of TRAb in the diagnosis of GD at presentation was 98.4%/62.9% at 1.75 IU/L and 91.2%/90.12% at 3.37 IU/L, respectively.

Conclusion

The TRAb test is a sensitive test to differentiate between subjects with GD and NGD presenting with hyperthyroidism. However, the cutoff (1.75 IU/L) as per the kit manufacturer may lead to a lower specificity for diagnosis. A modified cut-off of 3.37 IU/L should be considered for optimizing the diagnostic efficacy of the test.

Follow-up of a case of subacute thyroiditis with uncommon thyroid (99m)Tc uptake

Thyroidal 99mTc uptake in the acute thyrotoxic phase of subacute thyroiditis (SAT) is always inhibited. However, a patient with SAT had signs in the right-side thyroid gland with transient thyrotoxicosis and slightly high 99mTc uptake levels in the right lobe, low 99mTc uptake in the left lobe, and normal overall uptake. Histological examination showed cellular destruction and granulomatous inflammatory changes in the right lobe, with marked interstitial fibrosis in the left lobe. The patient was thyrotrophin-receptor antibody (TRAb) positive. After a short course of prednisolone, SAT-like symptoms and signs improved. TRAb-positivity resolved spontaneously after 22 months, and TSH levels were slightly low for 22 months. Levels then kept normal in the following four years. In conclusion, high 99mTc uptake by the right lobe was due to the combined effects of TRAb and left thyroid gland fibrosis.

Study on cutoff value setting for differential diagnosis between Graves' disease and painless thyroiditis using the TRAb (Elecsys TRAb) measurement via the fully automated electrochemiluminescence immunoassay system

The purposes of this study are to set the Elecsys TRAb cutoff value by which GD and PT can be accurately diagnosed simply; and to investigate the usefulness of the vascularity index (VI) obtained from power Doppler sonography (PDS). Using 109 normal controls, 186 GD patients, and 109 PT patients who were diagnosed through Tc-99m uptake, we set the cutoff value by conducting ROC analysis on the Elecsys TRAb values. The cutoff value as a result of the ROC analysis on the Elecsys TRAb values of the normal controls and GD patients was 0.8 IU/L with 100% of sensitivity and specificity. Because all 89 cases (81.6% of the entire PT cases) with Elecsys TRAb =<0.8 IU/L are PT, the cutoff =<0.8IU/L can thus be diagnosed as PT. In contrast, because all 166 cases (88.7% of the entire GD) with Elecsys TRAb >=3.0 IU/L except for one case of PT are GD, the cutoff >=3.0 IU/L can be diagnosed as GD. So Elecsys TRAb between 0.8-3.0 IU/L was dubbed gray zone (GZ). Finally, the cutoff value of 1.5 IU/L from the ROC on the PT and GD cases was chosen as the cutoff with 96.2% of sensitivity and 94.6 of specificity. All PDS VI >=80% were GD including 4 of 6 cases with GZ and all PDS VI <50% plus Elecsys TRAb-negative cases were PT including 4 of 5 cases with GZ. In conclusion, Elecsys TRAb cutoff and VI value for differential diagnosis between GD and PT has been set successfully.

[Subacute thyroiditis with cell destruction and temporary hyperthyroidism in Graves'disease--case report]

We present the case of a 60-year old woman with painful swelling of the thyroid gland and temporary thyrotoxicosis. 30 years ago she had experienced a period of hyperthyroidism because of Graves' disease. This time thyrotropin-receptor-antibodies were negative, Tc-99 m scan revealed decreased uptake in both lobes (this pattern normalised later on) and fine needle aspiration presented leucocyte infiltration of the thyroid. Three months later hypothyroidism was observed requiring treatment with levothyroxine. The development of subacute thyroiditis and Graves' disease in the same person is rare, autoimmune factors and a possible relationship are discussed.

Relapse of Graves' disease after subacute thyroiditis

We report the case of a 46-year-old man whose Graves' disease relapsed 5 years after its first appearance. At the time of relapse thyrotropin (TSH) receptor antibodies were very high, as was radioactive uptake in the left lobe of the thyroid. After thyroidectomy, histological analysis of the specimen showed evidence of treated Graves' disease, and there were signs of subacute thyroiditis in the right lobe. The clinical and immunologic characteristics of this observation are discussed as well as the hypothesis explaining the succession of an inflammatory and autoimmune thyroid disease.

Evaluation of infectious etiology in subacute thyroiditis--lack of association with coxsackievirus infection

The etiology of subacute granulomatous thyroiditis (SAT) is obscure, although it is postulated to be associated with viral infections and genetic factors. In the present study, the possibility of an infectious etiology was prospectively studied in 27 consecutive patients with SAT. Special emphasis was put on the role of enteroviruses. Coupled sera (interval one month) were taken from all patients and single sera from 29 control subjects for virus antibody determinations. Stool samples were collected for virus isolation and fine-needle aspiration samples from thyroid gland for the detection of enterovirus RNA using RT-PCR were taken from SAT patients. Enteroviral antibodies were tested using three different methods: indirect EIA, heavy chain capture RIA, and standard complement fixation (CF) test. Antibodies against other common viral pathogens, including enteroviruses, were screened using the CF test and those against Mycoplasma pneumoniae and Chlamydia pneumoniae using EIA and microimmunofluorescence techniques, respectively. Common respiratory viruses were also screened from nasopharyngeal suction samples by antigen detection EIA. Based on serological findings, one patient had acute Cytomegalovirus infection. All other patients were negative in antibody tests, virus isolation, RT-PCR, and antigen detection. Enterovirus RNA was not detected by PCR in the thyroid tissue in any of the fine-needle aspiration samples. There was no evidence of recent enteroviral infections in SAT patients. The results suggest that SAT is not usually associated with acute infections. No evidence was obtained to support the proposed role of enteroviruses as an important etiologic agent of SAT.

Pertechnetate thyroid uptake is not always suppressed in patients with subacute thyroiditis

The authors studied the clinical courses and immunologic aspects in 15 patients (age range, 32-69 years old; 14 women) with clinical features that were similar to subacute thyroiditis (SAT). In 2 patients (group A) whose thyrotropin-binding inhibitory immunoglobulins (TBII) and thyroid stimulating antibody (TSAb) showed strongly positive activity at the initial visit, Tc-99m pertechnetate thyroid uptake (Tc-99m uptake) was elevated (5.6% and 3.8%, respectively, normal; 0.7-3.0%). In 6 (group B) of 13 other patients, Tc-99m uptake was not completely suppressed (2 normal, 4 near normal) and imaging showed uptake in one lobe. In 7 (group C), however, there was no evidence of uptake in either lobe. Inflammatory process was localized in one lobe in all group B patients, and was in both lobes in all group C patients but one. Serum TSH levels were detectable in at least 4 patients (2 group B, 2 group C) low in all. There were no patients in both groups B and C in whom TBII and/or TSAb were detected at the initial visit. In SAT, marked suppression of Tc-99m uptake may be ascribed mainly to inflammatory follicular cell damage, but it is not always suppressed, owing to an association similar to Graves' disease and other unknown mechanism(s).

The transition of subacute thyroiditis to Graves' disease as evidenced by diagnostic imaging

The development of Graves' disease as evidenced by diagnostic imaging and appearance of TSH receptor antibodies is described in a 49-year-old woman 6 months after onset of subacute thyroiditis. The HLA typing indicated that the patient had a genetic predisposition to hyperthyroid Graves' disease as well as subacute thyroiditis. A possible causal relationship is discussed.