Unraveling the Link: Seizure Characteristics and Ammonia Levels in Urea Cycle Disorder During Hyperammonemic Crises

Background

This retrospective clinical study performed at a single clinical center aimed to identify the prevalence of seizures in individuals with urea cycle disorders (UCDs) with and without hyperammonemic (HA) crises. In addition, we sought to correlate the utility of biochemical markers and electroencephalography (EEG) in detecting subclinical seizures during HA.

Methods

Medical records of individuals with UCDs enrolled in Urea Cycle Disorders Consortium Longitudinal Study (UCDC-LS) (NCT00237315) at Children's National Hospital between 2006 and 2022 were reviewed for evidence of clinical and subclinical seizuress during HA crises, and initial biochemical levels concurrently.

Results

Eighty-five individuals with UCD were included in the analyses. Fifty-six of the 85 patients (66%) experienced HA crises, with a total of 163 HA events. Seizures are observed in 13% of HA events. Among all HA events with concomitant EEG, subclinical seizures were identified in 27% of crises of encephalopathy without clinical seizures and 53% of crises with clinical seizures. The odds of seizures increases 2.65 (95% confidence interval [CI], 1.51 to 4.66) times for every 100 μmol/L increase in ammonia and 1.14 (95% CI, 1.04 to 1.25) times for every 100 μmol/L increase in glutamine.

Conclusions

This study highlights the utility of EEG monitoring during crises for patients presenting with clinical seizures or encephalopathy with HA. During HA events, measurement of initial ammonia and glutamine can help determine risk for seizures and guide EEG monitoring decisions.