Diagnostic Accuracy of Clinical, Biochemical and Ultrasonographic Parameters for Differentiating Graves' Disease from Destructive Thyroiditis

ABSTRACT Background: Graves' disease (GD) and destructive thyroiditis (DT) both cause thyrotoxicosis but need opposite management: antithyroid drugs or definitive therapy for GD, and symptomatic care for self-limiting DT. The 99mTc thyroid uptake scan separates them reliably but is not available everywhere and is unsuitable in pregnancy and lactation. We assessed how well clinical, biochemical and ultrasonographic parameters distinguish GD from DT when a scan is unavailable in resource limited settings. Methods: In this study, 102 patients with thyrotoxicosis were classified by 99mTc scan uptake as GD (increased uptake, n = 54) or DT (decreased uptake, n = 48). Clinical features, TSH, free and total T4, total T3, T3/T4 ratio, ESR, TSH receptor antibody (TRAb), thyroid volume and Doppler peak systolic velocity of the superior (PSV-STA) and inferior (PSV-ITA) thyroid arteries were compared. Diagnostic performance was assessed by receiver operating characteristic (ROC) analysis. Results: TRAb had the highest accuracy (AUC 0.949; cut-off ≥ 3.7 IU/L; sensitivity 81.5%, specificity 97.9%). Among other parameters, total T3 (AUC 0.895; > 2.2 ng/ml; sensitivity 98.1%, specificity 79.2%), PSV-STA (AUC 0.891; ≥ 47 cm/s; 87.0%, 81.2%), PSV-ITA (AUC 0.845; ≥ 40 cm/s; 79.6%, 83.3%) and T3/T4 ratio (AUC 0.816; ≥ 14.7; 85.2%, 68.7%) performed best for differentiating GD from DT. Conclusion: When a 99mTc scan is unavailable, TRAb is the best single test; where TRAb is also lacking particularly in resource limited settings, thyroid arterial Doppler velocity and total T3, can separate GD from DT with good accuracy. Keywords: Graves' disease; destructive thyroiditis; thyrotoxicosis; TSH receptor antibody; thyroid Doppler; peak systolic velocity; T3/T4 ratio; ROC curve