Nonconvulsive status epilepticus (NCSE) is common in patients with coma with a 
prevalence between 5% and 48%. Patients in deep coma may exhibit epileptiform 
EEG patterns, such as generalized periodic spikes, and there is an ongoing 
debate about the relationship of these patterns and NCSE. The purposes of this 
review are (i) to discuss the various EEG patterns found in coma, its 
fluctuations, and transitions and (ii) to propose modified criteria for NCSE in 
coma. Classical coma patterns such as diffuse polymorphic delta activity, 
spindle coma, alpha/theta coma, low output voltage, or burst suppression do not 
reflect NCSE. Any ictal patterns with a typical spatiotemporal evolution or 
epileptiform discharges faster than 2.5 Hz in a comatose patient reflect 
nonconvulsive seizures or NCSE and should be treated. Generalized periodic 
diacharges or lateralized periodic discharges (GPDs/LPDs) with a frequency of 
less than 2.5 Hz or rhythmic discharges (RDs) faster than 0.5 Hz are the 
borderland of NCSE in coma. In these cases, at least one of the additional 
criteria is needed to diagnose NCSE (a) subtle clinical ictal phenomena, (b) 
typical spatiotemporal evolution, or (c) response to antiepileptic drug 
treatment. There is currently no consensus about how long these patterns must be 
present to qualify for NCSE, and the distinction from nonconvulsive seizures in 
patients with critical illness or in comatose patients seems arbitrary. The 
Salzburg Consensus Criteria for NCSE [1] have been modified according to the 
Standardized Terminology of the American Clinical Neurophysiology Society [2] 
and validated in three different cohorts, with a sensitivity of 97.2%, a 
specificity of 95.9%, and a diagnostic accuracy of 96.3% in patients with 
clinical signs of NCSE. Their diagnostic utility in different cohorts with 
patients in deep coma has to be studied in the future. This article is part of a 
Special Issue entitled "Status Epilepticus".