[Discrepancy between 99mTc-HMPAO and 99mTc-ECD in Alzheimer's disease: does the retention mechanism depend on the disease?].

The discrepancy between 99mTc-hexamethyl-propyleneamine oxime (HMPAO) and 99mTc-ethyl cysteinate dimer (ECD) in Alzheimer's disease (AD) was investigated and compared with in cerebral ischemic disease (CID). The subjects were fourteen AD and thirty-one CID patients with clinically reasonable rCBF reduced lesion on 133Xe SPECT. The subjects did not include the cases of acute and subacute CID. These SPECT were performed within two weeks by ring-type dynamic SPECT (HEADTOME, Shimadzu, Japan). In the CID group, both of HMPAO and ECD SPECT could hardly detect the mildly reduced rCBF lesion on 133Xe SPECT but normal on X-CT. In the case of AD group, the rCBF-reduced lesion on 133Xe SPECT could be detected well by ECD SPECT, but the HMPAO hardly detected the reduced lesion. This discrepancy between HMPAO and ECD may be due to the difference of the retention mechanism. In the case of AD, the injury of esterase activity that participates with the ECD retention may be more notable than that of glutathione activity for the HMPAO retention. These results suggest suggest that the reduction of ECD or HMPAO density depends directly on the insufficiency of retention mechanism rather the than rCBF reduction. And the insufficiency of this retention mechanism depends on also type of the disease i.e. AD or CID.