This chapter uses a case-based approach to describe electrographic patterns associated with coma. These are rare and, though non-specific, may suggest particular underlying etiologies. The electrographic pattern of extreme delta brush (EDB) may be seen with anti-NMDA receptor encephalitis. Alpha-coma is a pattern of continuous unreactive alpha or alpha-theta range activity that may be seen in coma after cardiac arrest or in those with pontine injury. It may resemble normal wakefulness. Spindle-coma and beta-coma are also described. Electrocerebral inactivity (ECI) is the absence of all non-artifactual electrical activity on an EEG, when recording using minimal specified technical standards in patients with cerebral death (brain death).

The basic approach to an encephalopathic EEG consists of diagnosing encephalopathy, estimating its severity, identifying repetitive patterns and NCSE, if present. The three cardinal electrographic features of encephalopathy include background slowing, amplitude attenuation/suppression and loss of reactivity. Severe encephalopathies are typically characterized by a low amplitude, slow and unreactive record, while a reversal of these trends may indicate improvement. Estimation of severity differs from prognostication. Repetitive patterns (rhythmic and periodic) are common in encephalopathic patients and have important implications regarding etiology, epileptogenicity and prognosis. NCSE results from electrographic ictal activity that contributes to the encephalopathic state. It should be diagnosed based on clinical signs, EEG findings and a response to antiepileptic medications. NCSE is independently associated with increased mortality. Spindle coma is characterized by slow background with frequent symmetric spindles, typically has a favorable prognosis in those with reactivity and without evidence of structural damage. Alpha coma consists of unreactive alpha frequencies, they have a posterior predominance in brainstem lesions and an anterior or diffuse distribution with cerebral anoxia. Posterior predominant alpha coma should be differentiated from a locked-in syndrome. Beta coma typically occurs from drug overdose and usually has a favorable prognosis. CJD and SSPE are infectious encephalopathies with distinct electrographic presentations that typically consists of GPDs. Extreme delta brush pattern commonly occurs in Anti-NMDA receptor encephalitis.