Ictal cerebral blood flow in psychogenic non-epileptic seizures: a preliminary SPECT study

Understanding the mechanism of psychogenic non-epileptic seizures (PNES) is challenging. A recent review grouped currently hypothesised psychological models into four: (1) traumatic dissociation, (2) hard-wired anxious-arousal responses, (3) conversion defences and (4) conditioned behaviours, but concluded that determining which of these was correct, if any, went far beyond the available evidence.1 Patients’ subjective reports may lend striking support to some models, but are necessarily post-hoc, and susceptible to iatrogenic suggestion.2 Neuroimaging, such as functional MRI, provides more objective evidence, but is typically restricted to the inter-ictal phase because of potential movement during the scan.3 Single photon emission computed tomography (SPECT) would have distinct advantages in imaging of the peri-ictal state as the tracer injection and uptake occur at the time of the seizure while the scanning can be completed later, after the seizure has finished, overcoming the motion issues. The ictal scan could then be compared with an inter-ictal SPECT to determine the ictal contribution to cerebral blood flow. This process is standard for epilepsy surgery workup, and we combined the databases from two epilepsy surgery centres to find opportunistic cases where the ictal scans of potential surgery cases proved to be of PNES—either because the initial epilepsy diagnosis was mistaken or because the scan captured a comorbid non-epileptic …