SPECT-negative SIRPIDs argues against treatment as seizures

Stimulus-induced rhythmic, periodic, or ictal discharges (SIRPIDs) are a recently described form of epileptiform periodic discharges evoked by arousal. Similar to other periodic discharges (e.g., pseudoperiodic lateralized epileptiform discharges, generalized periodic epileptiform discharges, bilaterally independent epileptiform discharges), SIRPIDs lie somewhere along an ictal-interictal continuum. To determine whether SIRPIDs represent an ictal phenomenon reflected by increased focal cerebral perfusion on single-photon emission computerized tomography, or conversely an interictal pattern, the authors tested a patient with nonconvulsive status confirmed on EEG, which evolved to SIRPIDs with a concomittant contralateral hemiparesis. To test the ictal-increased flow hypothesis, a single-photon emission computerized tomography scan was obtained during a stimulus-induced train of rhythmic discharges on EEG, but it revealed no increase in tracer uptake. The authors conclude that SIRPIDs did not increase regional cerebral blood flow as would seizures. Thus, the evidence indicates little if any metabolic/blood flow activation with SIRPIDs, thus tempering the intensity with which SIRPIDs might be managed. This provides a testable paradigm for future patterns of uncertain epileptic significance.