Thyroid scintigraphy in diagnosis of multinodular euthyroid goiter and functional thyroid autonomy

Abstract

Aim of the study. To estimate the meaning of thyroid suppression test as the method for diagnosis of functional thyroid autonomy (FA). Materials and methods. The main group consisted of 50 patients (46 females, 4 males) older 40 yrs with multinodular euthyroid whose basal scintigraphy demonstrated one or more areas of increased Tc 99m thyroid uptake. Twenty two individuals of control group (27.5 [23; 38.75] yrs) with no thyroid abnormalities underwent only basal thyroid scintigraphy. Thyroid suppression test protocol for the main group included 10 - 14 days of 2 μg/kg L-thyroxin (L-T4) intake prior to repeated scintigraphy under suppression. Results. Basal TcTU in control group was significantly lower (1.51% [1.16; 1.76]) than in the main group (1.67% [1.4; 2.2]). TcTU of the main group did not correlate with thyroid volume (r = 0.012; p = 0.9), “hot” nodule volume (r = 0.08; p = 0.5), TSH (r = 0.026; p = 0.9), and thyroid hormones levels. Thyroid suppression test reviled FA in 62% (31/50) patients. TcTU under suppression (TcTUs) in the main group of 50 patients was 0.87% [0.76; 0.87]; it was significantly lower than TcTU (W = 1275; p < 0.001). TcTUs did not depend upon thyroid volume (r = -0.097; p = 0.501), in contrast to TcTU it was a weak negative correlation with basal TSH level (r = -0.328; p = 0.020), a weak positive correlation with basal fT4 (r = 0.38; p = 0.007) and fT3 levels (r = 0.54; p < 0.001), moderate positive correlation with “hot” nodules volume. Comparing the patients who developed thyrotoxicosis with those who stayed euthyroid showed that the usage of Tc 99m uptake decrease degree (%) while suppression from the basal, but not TcTUs, is more effective for individual prognosis of thyrotoxicosis development. Patients who demonstrate the decrease of Tc 99m uptake less than 30-35% while thyroid suppression test have the biggest risk of FA decompensation and thyrotoxicosis development independently of absolute TcTUs values.