Cardiac sympathetic innervation imaging by 123I-MIBG has been widely adopted in evaluating Pts affected by congestive heart failure (CHF) to assess prognosis, response to treatment, risk of ventricular arrhythmias and sudden death and prediction of response to cardiac resynchronization therapy. The same tracer has been used in patients with neurological disease to assess the state of the cardiac sympathetic nervous system at a post-ganglionic level that is altered in patients with Parkinson disease (PD), even without clinical signs of dysautonomia, and normal in other Parkinsonism such as multisystem atrophy (MSA). Both cardiological and neurological pts are pretreated with Lugol’s oral solution and/or potassium perchlorate to prevent thyroid uptake of unlabeled 123I and to limit the thyroid radiation exposure. However, despite the inhibition of the iodide pump a thyroid visualization is frequently observed in MIBG scans in pts imaged for cardiac or neurological disorders. Recently a pt with hyperthyroidism, normal calcitonin level and CHF came to our observation for MIBG imaging. There was a high thyroid uptake of the tracer despite he was on therapy with Amiodarone. A scan with 123I-Iodide confirmed the absence of any uptake.
Aim of the study was the evaluation of the thyroid uptake in pts undergone to 123I-MIBG scan for CHF and movement disorders.
We have reviewed the 123I-MIBG scintigraphies of 57 pts recruited in three different centres (Brescia, Castelfranco Veneto and Veruno) who were imaged at 15’ and 4 h and in whom the thyroid was included in the field of view of the thorax. 42 pts underwent MIBG imaging for cardiological purposes and 15 for neurological disorders. 2/3 centres pretreated the pts with Lugol’s oral solution and/or potassium perchlorate and one centre did not and the pts were referred as control group. The following parameters were evaluated. Tracer wash out from heart (HWO) and thyroid (TWO), heart to mediastinum ratio (H/M), thyroid to mediastinum ratio (T/M) at 15’ and 4h
In the cardiac pts HWO was 23±7.2% and TWO was 11.4±8.2% (p<.0001). The TWO was 12.2±13.4% in centres 1 and 2 and 10.05±8.97% in centre 3 (control group), p=n.s. The T/M ratio was 1.37±0.17 in Centre 1-2 and 1.3±0.35 in Centre 3 p=n.s.(Control group- no pretreatment).
In neurological pts the HWO was 26±8,1% and the TWO was 20,32c6,41, p<.05. The difference in TWO was statistically significant (p<.01) between cardiological and neurological pts, whereas the HWO was not (p=ns). The 4h H/M was 1.49±0.23 in cardiological pts and 1,4±0.39 in neurological pts (p=n.s.) The 4h T/M was 1.33±0.3 in cardiological pts and 1,15±0.13 in neurological pts (p<0.05).
In conclusion, the thyroid visualization in MIBG imaging is not related to accumulation of 123I-iodide but to 123I-MIBG uptake as an expression of thyroid sympathetic innervation. On the basis of our observation pretreatment with Lugol’s oral solution and/or potassium perchlorate is therefore not justified and the procedure guidelines should be revised. Different values of TWO and T/M ratio in cardiological and neurological disorders probably express a different attitude of thyroid dopaminergic receptors in more generalized sympathetic disorder in Parkinson’s disease rather than an activation of the sympatho-adrenergic system in CHF.

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