Lateralized periodic discharges frequency correlates with glucose metabolism

Abstract

Objective: To investigate the correlation between characteristics of lateralized periodic discharges (LPDs) and glucose metabolism measured by ¹⁸F-fluorodeoxyglucose (FDG)-PET.

Methods: We retrospectively reviewed medical records to identify patients who underwent FDG-PET during EEG monitoring with LPDs present during the FDG uptake period. Two blinded board-certified neurophysiologists independently interpreted EEGs. FDG uptake was measured using standardized uptake value (SUV). Structural images were fused with PET images to aid with localization of SUV. Two PET readers independently measured maximum SUV. Relative SUV values were obtained by normalization of the maximum SUV to the SUV of pons (SUVRpons). LPD frequency was analyzed both as a categorical variable and as a continuous measure. Other secondary variables included duration, amplitude, presence of structural lesion, and "plus" EEG features such as rhythmic or fast sharp activity.

Results: Nine patients were identified and 7 had a structural etiology for LPDs. Analysis using frequency as a categorical variable and continuous variable showed an association between increased LPD frequency and increased ipsilateral SUVRpons (p = 0.02). Metabolism associated with LPDs (0.5 Hz as a baseline) increased by a median of 100% at 1 Hz and for frequencies >1 Hz increased by a median of 309%. There were no statistically significant differences in SUVRpons for other factors including duration (p = 0.10), amplitude (p = 0.80), structural etiology (p = 0.55), or "plus" features such as rhythmic or fast sharp activity (p = 0.84).

Conclusions: Metabolic activity increases monotonically with LPD frequency. LPD frequency should be a measure of interest when developing neuroprotection strategies in critical neurologic illness.

Figure 1. Axial PET slice at the region of maximal relative standardized uptake value of the pons (SUVRpons) for each of the 9 patients

There is a 10-color scheme covering the range of 0–3 for the SUVRpons (shown on the scale to the right of the figure). The numbers in the right-hand corner correspond to subject number. The row headings reference the frequency of the lateralized periodic discharges corresponding to the EEG obtained during the FDG uptake period.

Figure 2. Boxplot and scatterplot

(A) Boxplot of the binned frequencies with 3 patients in each category (<1 Hz, 1 Hz, >1 Hz).The overall p value for the permutation testing comparing multiple categories is significant at 0.02; tests between categories were not: p = 0.20 (<1 Hz|1 Hz), p = 0.22 (1 Hz|>1 Hz), and p = 0.10 (<1 Hz|1 Hz). Median (range) relative standardized uptake values (SUVR) (Pons) are <1 Hz: 1.1 (1.2–1.5), 1 Hz: 2.2 (1.5–2.8), >1 Hz: 3.4 (2.8–3.7). (B) Scatterplot with a regression line fitted with least square regression. F-statistic p value is significant at 0.013 with an R² value of 0.61, coefficient 1.1. LPD = lateralized periodic discharges.