Dissociation of 99mTc-ECD and 99mTc-HMPAO distributions in herpes simplex encephalitis

In herpes simplex encephalitis (HSE), the authors noted an evident dissociation between the ^99mTc-ethyl cysteinate dimer (ECD) and ^99mTc-d,l-hexamethyl-propylene- amine oxime (HMPAO) single photon emission computed tomographies (SPECTs). The patient was a 5-year-old boy with diffuse type of pontine glioma, which was treated with hyperfractionated radiotherapy. Two weeks after the completion of radiation therapy, a lesion suggesting that of HSE was noted in the right frontotemporal region on magnetic resonance images. ^99mTc-HMPAO SPECT showed an increased accumulation of the tracer in this lesion. On the ^99mTc-ECD dynamic SPECT, an exaggerated accumulation of the tracer was noted within 80 s of administration, followed by a rapid drop in the accumulation, resulting in a low accumulation in 10 min. It was assumed that this dissociation was due to the different mechanisms to trap HMPAO and ECD in the brain tissue. Received: 30 September 1995 Revised: 29 February 1996