REGIONAL LUMPED CONSTANT DIFFERENCES AND ASYMMETRY IN FLUORINE-18-FDGUPTAKE IN TEMPORAL-LOBE EPILEPSY

To date, there has been no satisfactory explanation for the observatio n that interictal uptake of the glucose analog [F-18]fluorodeoxyglucos e (FDG) is consistently reduced in the temporal robe ipsilateral to th e seizure focus in patients with temporal lobe epilepsy, We examined t he hypothesis that regional differences in tracer uptake in temporal l obe epilepsy reflect regional differences in the lumped constant (Lamb da). Methods: In 9 control subjects and 10 patients with temporal lobe epilepsy, we obtained regional estimates of Lambda by expressing Lamb da in terms of transfer coefficients for FDG and parameters which are likely to remain constant throughout both the brain and under differen t functional states, Results: In the patients, Lambda was lower in the temporal lobe ipsilateral to the epileptic focus (0.53 +/- 0.06; p < 0.005) than in the contralateral temporal lobe (0.56 +/- 0.06), Inters ide differences in Lambda were highly correlated with asymmetry in tra cer uptake, Furthermore, the use of regional estimates of Lambda reduc ed the asymmetry in estimated rCMR(glc) in patients with temporal lobe epilepsy but not in controls, Conclusion: In these patients, a change in tracer uptake may not indicate a change in glucose consumption of corresponding magnitude, raising the possibility that in at least some patients with temporal lobe epilepsy, the term hypometabolism does no t accurately describe reductions in tracer uptake.