Abstracts

Rationale: The electrographic and clinical significance of stimulus-induced rhythmic, periodic or ictal discharges (SIRPIDs) remains unclear and the debate of its ictal origin remains open. We report the findings of single photon emission computed tomography (SPECT) in 4 patients with SIRPIDs. Methods: Four consecutive patients with SIRPIDs were identified prospectively during continuous video-EEG (cVideo-EEG) monitoring. SPECT with 25-31.3 mci 99 mTC-ED injection was performed at the bedside immediately after sensory stimulation was applied and SIRPIDs were noted. Results: Patient 1- A76 year old man with terminal myelodysplastic disorder, was admitted for a self inflicted gun shot wound to the head. He had a complicated hospital course. He was evaluated with 3 days of cVideo-EEG) monitoring after he was found to be in non-convulsive status epilepticus (NCSE). After receiving fosphenytoin, SIRPIDs were identified. SPECT injection was obtained on the second day of monitoring. The study showed diffuse mild increase of tracer uptake in the left occipital cortex. His anti-epileptic drug (AED) regimen was optimized. Patient 2- A 52 year old woman with history of traumatic brain injury, epilepsy and chronic renal failure on hemodialysis was evaluated for mental status changes with 5 days of cVideo-EEG monitoring. She was initially taking phenytoin and eventually levetiracetam was added. Due to logistical reasons, the injection of the radionuclear tracer was done on the fifth day of monitoring. The study showed a localized site of increased uptake in the left parietal cortex. It was unclear however if this finding represented motor activation or an ictal focus. Because of this ambiguous finding and improvement in her mental no change in her AEDs was made. Patient 3- A 79 year old lady with multiple medical problems and an acute right frontal stroke was found to be in NCSE. Fosphenytoin was initiated and was followed by levetiracetam. She underwent monitoring with 3 day cVideo-EEG which showed SIRPIDs. SPECT injection was obtained on the third day of monitoring and did not show any abnormal uptake of the tracer. No changes were made to her AEDS. Patient 4- A 77 year old women with multiple medical problems, including kidney transplant was found to be in NCSE. Intravenous valproic acid was administered. She underwent 4 day cVideo-EEG monitoring. After SIRPIDs were identified a SPECT injection was obtained. The study did not show any abnormal uptake of the tracer. No changes were made to her AED regimen. Conclusions: Our results indicate that SPECT imaging is feasible despite technical aspects such as logistical issues encountered in the critically ill. SPECT imaging with injection of the radionuclear tracer at the time of SIRPIDs is a useful tool in guiding treatment with AEDs.