The relationships between changes in myocardial uptake of metaiodobenzylguanidine (
MIBG) and those in circulating
catecholamines and cardiac function
after treatment of phaeochromocytoma and
neuroblastoma were evaluated.
Iodine-123 or
iodine-131 MIBG scintigraphy was performed before and after surgical resection and/or
chemotherapy for primary tumours in nine patients with phaeochromocytoma and 13 patients with
neuroblastoma. Changes in myocardial
MIBG uptake
after treatment were estimated by the heart-to-upper mediastinum (H/M) uptake ratios on the images obtained 24 h after
MIBG injection, which were compared with serum levels of
noradrenaline (NA) and
adrenaline (A). Cardiac function was assessed by echocardiography, with measurements of the left ventricular ejection fraction (LVEF). Before treatment, eight patients with phaeochromocytoma and three with
neuroblastoma showed poor myocardial
MIBG uptake, with highly elevated circulating NA and A. Echocardiography, however, did not show cardiac dysfunction in these patients with the exception of two patients with phaeochromocytoma. With normalization of NA and A levels
after treatment, all of these patients except for the two with persistent cardiac dysfunction showed restoration of myocardial
MIBG uptake. The H/M ratios increased significantly
after treatment in both patient groups, i.e. with phaeochromocytoma and with
neuroblastoma (P<0.0001 and P<0.05, respectively), and these ratios correlated inversely with circulating NA and A before and
after treatment. By contrast, there was no significant correlation between H/M ratios and LVEF in these two groups. These results indicate that suppression of myocardial
MIBG uptake usually may not be related to cardiac dysfunction and may be reversible following normalization of excess
catecholamine levels
after treatment in patients with neuroadrenergic tumours. However, the suppression may persist in the presence of
catecholamine-induced cardiac dysfunction. The assessment of myocardial
MIBG uptake can be a helpful adjunct in monitoring the normalization of circulating
catecholamine levels and also in identifying the presence of cardiac dysfunction in treated patients with neuroadrenergic tumours.