Investigation of parasympathetic and sympathetic cardiac innervation in diabetic neuropathy: heart rate variation versus meta-iodo-benzylguanidine measured by single photon emission computed tomography.

In diabetic neuropathy disturbed autonomic cardiac innervation is associated with shortened life expectancy. Sympathetic dysfunction is likely to play a role in cases of cardiac death. The quantitative uptake of the radiopharmaceutical iodine-123-meta-iodo-benzylguanidine (MIBG) can be measured by single photon emission computed tomography (SPECT). It is an index of the functional integrity of sympathetic neurones in the heart. The respiratory heart rate variation--as assessed by a computerized device--reflects mainly parasympathetic cardiac innervation. In 25 diabetic patients and 19 healthy subjects MIBG-SPECT and heart rate variation tests were carried out. MIBG scans in all normal subjects showed homogeneous uptake of activity. In 12 out of 25 patients at least two heart rate variation tests were abnormal. MIBG-SPECT was more sensitive (abnormal in 17 out of 25). The lack of correlation between MIBG-SPECT results and spectral analysis of heart rate variation suggest that spectral analysis alone should not be regarded as an indicator of sympathetic cardiac innervation.