Changes in benzodiazepine receptor binding detected with SPECT in patients with cerebral infarction

SPECT (single photon emission computed tomography) using iomazenil (IMZ) as a ligand for benzodiazepine receptors has recently been developed. Feasibility of the technique for detecting neuronal damage in the cerebral cortex was evaluated in 17 patients with cerebral infarction, specifically, patients with internal carotid artery (ICA) thrombosis (n = 6), middle cerebral artery (MCA) thrombosis (n = 5) and embolism (n = 6). IMZ SPECT was performed 5 to 17 days after stroke. Following the injection of 123I-IMZ 167 or 222 MBq intravenously, images were obtained at 15 minutes (early image) and 180 minutes (late image). In 11 cases, 99mTc-HM-PAO (hexamethyl-propylamine oxime) SPECT was also performed to measure cerebral blood flow (CBF). MRI was performed in all cases to elucidate areas of infarct. Early images from IMZ SPECT correlated well with those from HM-PAO, suggesting that early scans using IMZ SPECT reflect mainly CBF. In late images from IMZ SPECT, observed lesions were consistent with infarcted areas on MRI in most cases. However, in 3 cases of ICA thrombosis, 1 case of MCA thrombosis and 1 case of embolism, late IMZ SPECT imaging showed that the affected area was wider than apparent infarcts on MRI, indicating that the cerebral cortex, which was intact on MRI, was also involved. In these patients, clinical signs of cortical involvement were observed as well. These results suggest that moderately reduced CBF may affect cortical neurons without inducing apparent infarct, and such damage can be detected with IMZ SPECT.