DISSOCIATION OF TC-99M-ECD AND TC-99M-HMPAO DISTRIBUTIONS IN HERPES-SIMPLEX ENCEPHALITIS

In herpes simplex encephalitis (HSE), the authors noted an evident dis sociation between the Tc-99m-ethyl cysteinate dimer (ECD) and Tc-99m-d ,1-hexamethyl-propyleneamine oxime (HMPAO) single photon emission comp uted tomographies (SPECTs). The patient was a 5-year-old boy with diff use type of pontine glioma, which was treated with hyperfractionated r adiotherapy. Two weeks after the completion of radiation therapy, a le sion suggesting that of HSE was noted in the right frontotemporal regi on on magnetic resonance images. Tc-99m-HMpAO SPECT showed an increase d accumulation of the tracer in this lesion. On the Tc-99m-ECD dynamic SPECT, an exaggerated accumulation of the tracer was noted within 80 s of administration, followed by a rapid drop in the accumulation, res ulting in a low accumulation in 10 min. It: was assumed that this diss ociation was due to the different mechanisms to trap HMPAO and ECD in the brain tissue.