Measurement of myocardial accumulation of I-123-metaiodabenzylguanidine for studying cardiac autonomic neuropathy in diabetes mellitus

The association of myocardial I-123-metaiodobenzylguanidine (MIBG) accumulation and autonomic neuropathy, as well as factors known to affect autonomic nervous function, were studied in a group of 12 diabetic patients representing different degrees of autonomic failure. The early myocardial uptake phase of I-123-MIBG was measured by calculating the peak net influx rate for the first 30 min after the I-123-MIBG injection and by single photon emission computed tomography (SPECT) imaging 1 h after the injection. The retainment of I-123-MIBG in the myocardium was measured using SPECT imaging 6 h after the injection, and myocardial uptake and the myocardium/liver uptake ratio were calculated. The 6-h myocardium/liver uptake ratio of I-123-MIBG was significantly (p < 0.05) lower in the diabetic patients with clinically evident autonomic neuropathy compared with those without autonomic neuropathy. Greater body mass index was associated with lower peak net influx rate and I-h myocardial uptake of I-123-MIBG, and greater diastolic blood pressure was associated with lower l-h myocardial uptake of I-123-MIBG, whether or not the patients had diabetic autonomic neuropathy. In conclusion, reduction in the 6-h myocardium/liver uptake ratio of I-123-MIBG is related to diabetic autonomic neuropathy. Because the early I-123-MIBG accumulation ion in myocardium is reduced in diabetic patients with greater body mass index and diastolic blood pressure, irrespective of autonomic neuropathy, our results encourage the use of the late myocardial accumulation of I-123-MIBG for studying sympathetic neuropathy in the diabetic heart.