Challenging the neuronal MIBG uptake by pharmacological intervention:: effect of a single dose of oral amitriptyline on regional cardiac MIBG uptake

Purpose: Imaging with metaiodobenzylguanidine (MIBG) is used for the assessment of neuronal dysfunction in various cardiovascular disorders. Although valuable information is obtained by resting MIBG imaging, it is conceivable that competitive interference with the re-uptake mechanism would exaggerate MIBG defects and might unmask subclinical neuronal dysfunction. Tricyclic antidepressants. such as amitriptyline. have been reported to significantly increase cardiac MIBG washout and inhibit uptake into presynaptic neurons. This study was undertaken to assess whether a single oral dose of amitriptyline could influence cardiac MIBG distribution. Methods: Six patients (aged 62-81 years, four males, two females) who had demonstrated a normal cardiac MIBG scan during work-up for movement disorders were studied. The patients underwent a second I-123-MIBG study after oral administration of 25 mg amitriptyline within I week. Single-photon emission computed tomography images were acquired at 4 h to assess the regional distribution of MIBG. after generation of polar maps and employing a 20-segment model. Mean percentage of peak activity was calculated for each segment at rest and after amitriptyline administration. Results: After amitriptyline administration, there was a decrease in regional MIBG uptake in 10 4 segments per patient [62/120 segments (52%): 37 segments with a 5-10% decrease, 25 segments with a >10% decrease]. This chance was statistically significant in lateral (P=0.003), apical (P<0.0001) and inferior (P=0.03) regions. Conclusion: A single oral dose of amitriptyline can induce changes in the uptake and retention of cardiac MIBG. indicating the feasibility of use of pharmacological intervention in cardiac neurotransmission imaging.