The prevalence and significance of nonuniform thyroid radio‐isotope uptake in patients with Graves’ disease

OBJECTIVE: To evaluate the prevalence and clinical significance of nonuniform technetium ((99m)Tc) uptake among patients with Graves’ disease (GD). DESIGN, PATIENTS AND MEASUREMENTS: Patients with GD, referred between July 2005 and March 2018, had Tc(99)‐ uptake scans and TSH‐receptor antibody (TRAb) measured before antithyroid drug (ATD) therapy. Risk of relapse after ATD cessation was monitored until June 2021 and compared between GD patients based on uptake patterns. RESULTS: Of the 276 GD patients (mean age, 49.8 years; 84% female), 25 (9.0%) had nonuniform Tc(99) uptake. At diagnosis, individuals with nonuniform uptake were older (mean age of 61.8 vs. 48.5 years, p < .001), had lower mean thyroid hormone levels (free thyroxine: 36.3 vs. 45.4 pmol/L, p = .04 and free triiodothyronine: 10.0 vs. 17.8 pmol/L, p < .001) and median TRAb levels (4.2 vs. 6.6 U/L, p = .04) compared with those with a uniform uptake. Older age was a significant predictor for the presence of nonuniform uptake in GD patients; odds ratio (95% confidence intervals) of 1.07 (1.03 – 1.10). The risk of relapse was similar in both groups after a median (IQR) follow‐up of 41 (13–74) months after ATD cessation (56.0% vs. 46.3%, respectively); hazard ratio (95% confidence intervals) of 1.74 (0.96–3.15). CONCLUSIONS: Nonuniform radio‐isotope uptake is seen in 1 in 11 patients with GD which could be misdiagnosed as toxic multinodular goitre if TRAb levels are not measured. Treatment of GD patients with nonuniform radio‐isotope uptake with ATD therapy as first‐line appears to be equally effective as compared with those with uniform uptake. TRAb testing should be the main diagnostic test for patients with suspected GD with radio‐labelled uptake scans being reserved for those who are TRAb negative.