Bilateral temporal hypometabolism in epilepsy

Positron emission tomography (PET) has proven useful in epilepsy surgery for its ability to identify unilateral temporal hypometabolism (UTH), which is predictive of good surgical outcome. The significance of bilateral temporal hypometabolism (BTH) is not known.

We identified all patients who had marked bilateral reduction in temporal lobe metabolism relative to the cerebellar hemispheres and compared their clinical features and treatment outcomes with those of control patients with UTH.

BTH was evident in 10% of PET scans for epilepsy at our institution. We compared these patients with age-matched controls with UTH. The BTH patients had a higher percentage of generalized seizures; were more likely to have bilateral, diffuse or extratemporal seizure onsets; and had bilateral or diffuse magnetic resonance imaging (MRI) findings. UTH patients were more likely to have unilateral mesial temporal atrophy on MRI. Even when electrical seizure onsets were well localized, surgical outcomes were markedly worse in these patients than in controls. Medical treatment was also less successful. Social and cognitive functioning was worse in the BTH group. The only death occurred in the group with BTH.

Patients with BTH have features distinct from those with UTH and have a worse prognosis for seizure remission after surgery.