OLFACTORY BEDSIDE TEST - A SIMPLE APPROACH TO IDENTIFY TEMPORO-ORBITOFRONTAL DYSFUNCTION

Background: Olfactory memory and discrimination are processed by the a nteromesial temporal cortex and the orbitofrontal cortex. Both functio ns may therefore be impaired in limbic epilepsy. Methods: Twenty-seven patients with mesial temporal lobe seizures (MTLS), 10 patients with neocortical seizures (NS), and 10 matched healthy control subjects und erwent evaluation for olfactory quality discrimination (OD) and delaye d recognition memory (OM). All patients were referred for presurgical evaluation. The olfactory tests were performed in a same-different par adigm with 10 seconds (OD) and 60 minutes (OM) between presentations o f the odors, using the standardized University of Pennsylvania Smell I dentification Test. The presentations were monorhinal in the OD and bi rhinal in the OM tests. The results were related to regional glucose m etabolism measured with fludeoxyglucose F 18 positron emission tomogra phy. Results: Patients with MTLS had an impaired OD ipsilateral to the epileptogenic region (P < .001) and a higher total number of errors ( including both tests) (P = .002). They also had lower OM scores, but n ot significantly lower than those of patients with NS (P = .05). The c ombined OM and OD tests correctly identified patients with MTLS with a sensitivity of 85% and a specificity of 90%, offering a correct later alization in 74% of patients. Patients with MTLS whose OD was more imp aired than OM differed from those with more impaired OM by having a si gnificant hypometabolism not only over the neocortex of the epileptoge nic temporal lobe (P = .02) but also in the ipsilateral anterior (P = .008) and orbitofrontal cortex (P = .007) (2-way analysis of variance) . Conclusions: Tests of olfactory function are useful in distinguishin g between NS and MTLS. The impairments of OM and OD can be dissociated in pathological states and therefore mediated by different structures .