TL-201 SCINTIGRAPHY DOES NOT ALLOW VISUALIZATION OF THE THYROID IN EUTHYROID AND HYPERTHYROID PATIENTS TREATED WITH AMIODARONE

A retrospective study was performed to evaluate the usefulness of thal lium scintigraphy for visualization of thyroid morphology and function . Moreover, applying absolute quantitation, we wished to confirm the q ualitatively reduced Tc-99(m) uptake reported by Wiersinga et al. [8] in both euthyroid and hyper thyroid patients treated with amiodarone. Over a period of 2 years (1995-96), 10 patients (group A; 2 females, 8 males, mean age 68.6 years, range 61-74 years) receiving amiodarone t reatment for cardiac arrhythmias for at least 4 months were referred f or exploration of either hyperthyroidism (n = 4) or for exclusion of p arathyroid adenoma (n = 6). During the same period, 17 patients (group B; 10 females, 7 males, mean age 62 years, range 19-91 years) referre d for Tc-TL subtraction scintigraphy, and in whom follow-up revealed n o thyroid or parathyroid pathology, were used as controls. In all pati ents, thyroid status was assessed by thyroid function tests. Tl-201 an d Tc-99(m) uptake was calculated as a percentage of the injected dose, taking account of net injected counts and background and isotope deca y correction. Original images were scored using a 2-point scoring syst em (0 = poor, 1 = fair or good). Uptake of both Tc-99(m) and Tl-201 wa s significantly reduced in group A (Tc-99(m): 0.16 +/- 0.21%; Tl-201: 0.30 +/- 0.21%; mean +/- S.D.) compared to group B (Tc-99(m): 1.58 +/- 1.07%; Tl-201: 0.72 +/- 0.37%) (P < 0.005). The mean relative reducti on in Tc-99(m) uptake was more pronounced (90% decrease) than that of Tl-201 (58% decrease). In group A, the Tc-99(m) and Tl-201 image quali ty was poor in 10 of 10 and 8 of 10 patients respectively. In group B, the Tc-99(m) and Tl-201 image quality was poor in 3 of 17 and 4 of 17 patients respectively. The decreased uptake of Tl-201 may reflect the inhibitory effect of iodides on adenyl cyclase and its stimulation by TSH. In conclusion, the data presented confirm the qualitatively redu ced pertechnetate uptake reported by Wiersinga et al. [8]. Furthermore , Tl-201 uptake by the thyroid in euthyroid or hyperthyroid patients t reated with amiodarone is also reduced. Although quantitatively less p ronounced, it does not allow proper visualization of the thyroid.