Chapter 5: Generalized Nonepileptiform Activity

General principle

• ▪ The EEG is unable to distinguish between different etiologies. The major usage of the EEG is to determine the severity of encephalopathy, prognosis, and response of treatment.

• ▪ Common etiology:

  • ▸ Metabolic, toxic, inflammation, anoxic, and degenerative diseases

• ▪ Few EEG patterns associated with more specific etiologies for the encephalopathy:

  • ▸ Periodic pattern:

    • Anoxic encephalopathy

    • Certain encephalitis

  • ▸ Triphasic waves (TWs) or 14- and 6-Hz positive spike bursts:

    • Metabolic encephalopathy Lithium and ifosphamide toxicity

  • ▸ High-voltage beta activity:

    • Benzodiazepine or barbiturate intoxication

  • ▸ Low-voltage fast patterns:

    • Alcohol withdrawal

  • ▸ Bursts of high-voltage delta activity interspersed with mixed frequencies:

    • PCP (angel dust) intoxication

• ▪ Prognosis in most EEG patterns is usually correlated with underlying diseases and reactivity of EEG to external stimuli.

  • ▸ Ischemic strokes and anoxic ischemia after cardiorespiratory arrest are almost completely irreversible.

  • ▸ Brain injury produced by head trauma, subdural hemorrhages, and some intracranial hemorrhages, in the absence of raised intracranial pressure, may be partially, moderately, or occasionally wholly reversible.

  • ▸ Electrical disturbances with seizures and status epilepticus (SE), metabolic, and some toxic encephalopathies may be completely reversible.

• ▪ Some particular patterns have been identified that may have some prognostic significance:

  • ▸ Poor prognosis

    • Triphasic waves (TWs).

    • Alpha coma (AC) patterns in patients with anoxic encephalopathy nonreactive to noxious stimuli.

    • Continuously diffuse polymorphic delta activity (unless due to a toxic/metabolic disturbance) typically bodes poorly for the patient, when these patterns are low voltage.

    • Marked bilateral suppression coma.

    • Burst-suppression (B-S) patterns.

  • ▸ Better prognosis:

    • Spindle coma (SC) patterns

    • Beta coma

• ▪ Severity:

  • ▸ Milder encephalopathy:

    • Spontaneous variability

    • Evidence of EEG reactivity to painful stimulation

      • ◊ Reduction of amplitude, increase in frequency, and reduction in the slow activity

      • ◊ Paradoxical activation, which is a period of more severe delta slowing following painful stimuli

  • ▸ Severe encephalopathy:

    • Invariant EEG—no spontaneous variability or reactivity to external stimuli

• ▪ Combination of diffuse and focal EEG abnormalities:

  • ▸ Associated focal process such as old infarction or tumor

  • ▸ Nonketotic hyperosmolar coma

  • ▸ Focal seizure

  • ▸ Herpes simplex encephalitis and Creutzfeldt-Jakob disease (CJD)

Selected specific conditions

Drug intoxication

• ▪ Generalized theta-delta activity with superimposed beta frequency activity is highly characteristic of sedative drug intoxication.

• ▪ With more severe intoxication, the fast activity shows a slower frequency (10–13 Hz), widespread distribution, but anterior predominance.

• ▪ In the absence of prominent slow activity, the anterior-dominant generalized fast activity caused by sedative drug intoxication produces an alpha and SC pattern in the EEG that is indistinguishable from that seen with severe anoxic encephalopathy.

• ▪ Phencyclidine (PCP) or ketamine is associated with a distinctive EEG pattern similar to that of subacute sclerosing panencephalitis (SSPE).

Anoxic encephalopathy

• ▪ EEG should be done at least 5–6 hours after resuscitation.

• ▪ B-S pattern or electrocerebral silence (ECS) does not carry as ominous prognosis as when they ...