Diagnosis of pediatric hyperthyroidism: technetium 99 uptake versus thyroid stimulating immunoglobulins

Treatment with antithyroid drugs is effective in conditions of increased thyroid hormone production (mostly Graves' Disease; GD), but not in subacute thyroiditis (SAT) or autoimmune thyroiditis (AIT). Positive thyroid stimulating immunoglobulins (TSI) make GD likely. However, not all children with GD have increased TSI. Uptake studies with (123)I or (99)Tc ((99m)Tc) provide accurate and rapid diagnosis but are expensive and involve radiation exposure. Our objective was to compare TSI with (99m)Tc uptake for diagnosis of pediatric hyperthyroidism.

We performed a retrospective chart review of hyperthyroid children who had both TSI estimation and (99m)Tc uptake assessment at presentation. Based on subsequent laboratory studies and follow-up, 37 had GD and 10 had non-GD thyroiditis. The TSI index was considered positive (TSI+) when it was above the upper limit of normal. (99m)Tc uptake was considered positive (Tc+) for any uptake >0.4% and negative (and low) (Tc-) for uptake ≤0.4%.

Forty-seven youth (83% females), aged 12.3±4.6 years, presented with a suppressed thyrotropin (TSH) and elevated free thyroxine and total triiodothyronine. All 37 patients with GD were Tc+ (100% sensitivity and specificity). The sensitivity of TSI for diagnosing GD was 84%, and the specificity was 100%. Six patients with GD were discordant with Tc+ but TSI-. Elevated TSI correlated with Tc+ (p=0.01) with a degree of agreement (kappa) of 0.69.

(99m)Tc has excellent specificity and sensitivity in diagnosing GD. Given additional costs of (99m)Tc (two and a half times as much as TSI), it is reasonable to reserve (99m)Tc uptake assessment for hyperthyroidism of unclear etiology and negative TSI.