Ex-SPECTing Success: predictors of successful SPECT radiotracer injection during pre-surgical video-EEG admissions.

OBJECTIVES: To determine predictors of successful ictal Single Photon Emission Computed Tomography (SPECT) injections during Epilepsy Monitoring Unit (EMU) admissions for patients undergoing presurgical evaluation for drug resistant focal epilepsy. METHODS: In this retrospective study, consecutive EMU admissions were analysed at a single centre between 2019-2021. All seizures that occurred during the admission were reviewed. 'Injectable seizures' occurred during hours when the radiotracer was available. EMU-level data were analysed to identify factors predictive of an EMU admission with a successful SPECT injection (successful admission). Seizure-level data were analysed to identify factors predictive of an 'injectable seizure' receiving a SPECT injection during the ictal phase (successful injection). A multivariate generalised linear model was used to identify predictive variables. RESULTS: 125 EMU admissions involving 103 patients (median 37 years, IQR27.0-45.5) were analysed. 38.8% of seizures that were eligible for SPECT (n=134) were successfully injected; this represented 17.4% of all seizures (n=298) that occurred during admission. Unsuccessful admissions were most commonly due to a lack of seizures during EMU-SPECT (19.3%) or no 'injectable seizures' (62.3%). Successful EMU-SPECT was associated with baseline seizure frequency >1 per week (95%CI 2.1-3.0, p <0.001) and focal PET hypometabolism (95%CI 2.0-3.7, p <0.001). On multivariate analysis, the only factor associated with successful injection was patients being able to indicate they were having a seizure to staff (95%CI 1.0-4.4, p=0.038). SIGNIFICANCE: Completing a successful ictal SPECT study remains challenging. Baseline seizure frequency of >1 per-week, a PET hypometabolic focus and a patient's ability to indicate seizure onset were identified as predictors of success. These findings may assist EMUs in optimising their SPECT protocols, patient selection, and resource allocation.