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EEG pattern of encephalopathy

Nonspecific patterns

  • ▪ Alpha rhythm slowing → theta slowing → delta slowing → loss of alpha rhythm → loss of normal faster activity → loss/attenuation of sleep architectures, abnormal arousal patterns and presence of frontal intermittent rhythmic delta activity (FIRDA) → loss of normal variability and state changes → loss of reactivity to external stimuli, burst-suppression (B-S) → electrocerebral inactivity (ECI).

Specific patterns

Generalized Periodic Epileptiform Discharges (GPEDs)

  • ▪ Anoxic encephalopathy

  • ▪ After status epilepticus (SE)

  • ▪ Toxic encephalopathy

  • ▪ Creutzfeldt-Jakob disease (CJD; GPEDs at approximately 1 Hz)

Triphasic Waves

  • ▪ Toxic/metabolic encephalopathy

  • ▪ NCSE

Periodic Lateralized Epileptiform Discharges (PLEDs)

  • ▪ Acute or subacute unilateral lesions

  • ▪ Most commonly seen in stroke and herpes simplex encephalitis

Normal or Near-Normal EEG

  • ▪ Psychogenic process or brainstem disease ((locked-in syndrome)

Diffuse polymorphic delta slowing (delta coma)

Figure 6-1.

Posterior Reversible Encephalopathy Syndrome (PRES); Diffuse Polymorphic Delta Activity with Posterior Predominance. A 10-year-old girl with microscopic polyangiitis and chronic renal failure developed visual hallucinations, lethargy, and new-onset seizures. She was on cyclophosphamide. After the visual hallucination, she was found to have elevation of her blood pressure. EEG shows continuously diffuse polymorphic delta activity (PDA) with occipital predominance. Head CT and MRI show diffuse white matter involvement, maximally expressed in the watershed areas in the two hemispheres. The patient recovered after cyclophosphamide was stopped, and the blood pressure was well controlled.

Diffuse slowing is the most common finding on the EEGs in posterior reversible leukoencephalopathy syndrome (PRES).1 The delta coma EEG pattern is usually seen with more advanced states of encephalopathy and coma. With progression to deeper stages of coma, it appears diffuse and is usually unreactive. Polymorphic delta comas are due to structural abnormalities involving subcortical white matter or profound metabolic coma.24

Posterior-predominant delta activity in this case is probably due to the predominant involvement of posterior head region in PRES.

Figure 6-2.

Posterior Reversible Encephalopathy Syndrome (PRES); Occipital Lobe Seizure. (Same patient as in Figure 6-1) The patient developed a new-onset seizure described as head and eyes deviating to the right side, associated with unconsciousness lasting for approximately 3 minutes. EEG shows ictal activity arising from the left occipital lobe during the seizure.

Occipital lobe seizures have been described as a major clinical manifestation of PRES. This suggests that occipital lobe seizures may play a significant role in the anatomical location of the signal changes, offering an alternative explanation for the posterior location of the lesions, instead of the hypothesis that a ...

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