Background: Periodic epileptiform discharges (PEDs) are a frequent finding in comatose patients undergoing continuous EEG (cEEG) monitoring, but their clinical significance is unclear. PET and SPECT studies indicate that PEDs can be associated with focal hypermetabolism and hyperemia, suggesting that in some cases this pattern may be ictal and potentially harmful. We hypothesized that frequent PED activity in comatose patients is associated with reduced likelihood of recovery of consciousness.
Methods: We identified all comatose patients treated in the Columbia neuro-ICU between June 2008 and August 2009 who underwent ten or more consecutive days of video cEEG monitoring (N = 67), and classified them into three groups: those with (1) prolonged PEDs (five or more consecutive days), (2) intermittent PEDs (at least one but fewer than five consecutive days), and (3) no PEDs. Outcome at discharge was assessed by the Glasgow Outcome Scale and classified as dead (GOS 1), vegetative (GOS 2), and command-following (GOS 3-5).
Results: Mean age was 56 years, mean admission Glasgow Coma Scale score was seven, and the median duration of cEEG monitoring was 18 (range 10-111) days. The most common diagnoses were hypoxic-ischemic encephalopathy (18%), subarachnoid hemorrhage (16%), epilepsy (15%), encephalitis (15%), metabolic encephalopathy (13%), and intracerebral hemorrhage (12%). 37% of patients (N = 25) had prolonged PEDs, 31% (N = 21) had intermittent PEDs, and 31% (N = 21) had no PEDs. Prolonged PEDs were associated with the presence of SIRPIDS (P = 0.009), electrographic seizures (P = 0.019), and number of AEDs administered (P < 0.0001). However, the presence of intermittent or prolonged PED activity had no impact on mortality (31% overall) or recovery of consciousness (command-following) at the time of discharge (36% overall).
Conclusion: Persistent spontaneous PED activity in comatose patients is associated with SIRPIDs and electrographic seizures, but has no impact on the likelihood of survival or recovery of consciousness.