Neuropsychological functioning, FDG-PET hypometabolism and postsurgical seizure outcome in medically intractable focal epilepsy

Patients with medically intractable focal epilepsy complete a range of clinical investigationswhen investigated for possible surgery, typically including fluorodeoxyglucose positronemission tomography (FDG-PET) and detailed neuropsychological assessment. FDG-PEThypometabolism often extends beyond the epileptogenic focus, particularly in temporal lobeepilepsy (TLE), but the cause and significance of these distant metabolic abnormalities is notwell understood. Similarly, neuropsychological deficits in TLE can be widespread and extendwell beyond the memory or language deficits synonymous with temporal lobe dysfunction. Thisthesis explores the relationship between hypometabolism and neuropsychological functioningin focal epilepsy patients being evaluated for surgery. Two of the three empirical studies in this thesis examine the neuropsychological correlates ofhypometabolism in and beyond the temporal lobes. The first study examines a cohort of patientswith structural occipital lobe epilepsy (OLE), establishing the comprehensiveneuropsychological profile of this syndrome before exploring whether verbal memoryimpairment is selectively associated with left temporal lobe hypometabolism. The second studyextends this line of enquiry by examining in a homogeneous cohort of mesial temporal lobeepilepsy (MTLE) patients whether unilateral temporal lobe hypometabolism correlates withmaterial-specific episodic memory impairment, and whether performance on frontal lobeneuropsychology tests correlates with hypometabolism of the prefrontal cortex. Combined, theresults from these studies support the hypothesis that episodic memory skills correlate withunilateral temporal lobe hypometabolism in the expected material-specific way. However,performance on frontal lobe tests is not correlated with prefrontal hypometabolism, suggestingthese tests are not good measures of frontal lobe functioning in isolation. The third study examines whether neuropsychological functioning can independently predictpostsurgical seizure outcome in MTLE when considered alongside other potential demographicand clinical predictors, including FDG-PET variables. The results suggest verbal memory, butno other neuropsychological variable, can predict seizure outcome in isolation but not over andabove FDG-PET results. These findings are discussed in terms of the implications for the roleof the clinical neuropsychologist in the evaluation of epilepsy surgery candidates.