What are pseudoperiodic epileptiform discharges on EEG?

Updated: Oct 09, 2019
  • Author: Alexis D Boro, MD; Chief Editor: Selim R Benbadis, MD  more...
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Pseudoperiodic lateralized epileptiform discharges (PLEDs) are EEG abnormalities consisting of repetitive spike or sharp wave discharges that are focal or lateralized over 1 hemisphere, recur at intervals of 0.5-5 seconds, and continue through most of a routine EEG study. They are seen most frequently in the setting of acute unilateral lesions such as cerebral infarctions, encephalitis, or tumors. In 1 study, almost 50% of patients with PLEDs had acute lesions, approximately 45% had chronic lesions, and the remainder had normal imaging. [12] When PLEDS occur in a patient with epilepsy, they often represent a postictal pattern. When PLEDs occur in patients with chronic lesions, significant metabolic derangement is often present.

PLEDs are usually self-limited and resolve after the acute phase of a cerebral insult. Rarely, they may persist on a chronic basis. Seizures often occur acutely in patients with PLEDS discovered on a routine EEG (the incidence may 50% or more [13, 14] ) but the electrographic seizure pattern is usually distinct from the PLEDs. Certain neurologic presentations, such as epilepsia partialis continua or transient confusional states, can be associated with PLEDs. When they have a clear-cut clinical correlate, PLEDs constitute an ictal pattern.

Bilateral independent PLEDs (BiPLEDs) are periodic complexes occurring asynchronously over both hemispheres. BiPLEDS may differ in morphology and site of maximal expression on each side. This is an uncommon EEG finding. In a series of 18 patients, the most common causes were anoxic brain injury (28%) and CNS infection (28%). [15] While BiPLEDs have been associated with herpes simplex encephalitis, the pattern can occur in other CNS infections as well. In this series, the clinical correlates of BiPLEDs differed somewhat from those of PLEDs. The incidence of coma is higher in BiPLEDs than in PLEDs (72% vs 24%) and the mortality rate is higher (61% vs 29%). The incidences of focal seizures, focal neurologic deficits, and focal imaging abnormalities are lower.

When pseudoperiodic discharges occur synchronously over both hemispheres, they are termed generalized or bilateral pseudoperiodic discharges (GPEDs or BiPEDs). GPEDs most often occur in the setting of anoxia where they suggest a poor prognosis. They are also associated with stroke, profound metabolic disturbance, intoxication, and Creutzfeldt-Jacob disease. When they occur at a low frequency (at intervals of about 0.25 Hz or less) and involve more prolonged and often stereotyped polyphasic discharges, diagnostic considerations include SSPE and intoxication with PCP and ketamine. When the complexes occur at low frequency at relatively low amplitudes against a voltage-depressed background, the pattern is termed burst suppression and is seen most often in anoxia and in the presence of general anesthetics.

Pseudoperiodic lateralized epileptiform discharges Pseudoperiodic lateralized epileptiform discharges (PLEDS) in a 45-year-old woman after a stroke. These sharply contoured waveforms phase-reverse over the right posterior temporal region. Their fields involve much of the right hemisphere.
PLEDs in an elderly patient with an acute right mi PLEDs in an elderly patient with an acute right middle cerebral artery infarction. These 0.5- to 1-Hz discharges with superimposed sharply contoured beta activities are more ictal-appearing than those seen in the previous example. Is this a seizure? See next image.
PLEDs in an elderly patient with an acute right mi PLEDs in an elderly patient with an acute right middle cerebral artery infarction. In the sixth second the interictal PLEDs are replaced by a clearcut evolving seizure pattern.
Ictal PLEDs. This patient underwent an elective le Ictal PLEDs. This patient underwent an elective left-sided evacuation of a subdural hematoma some months before this EEG was recorded. This study was done to evaluate right-sided myoclonic jerks and aphasia in the setting of a urinary tract infection. The myoclonic jerks were time-locked to the left-sided PLEDs in previous image. These discharges, the myoclonic jerks, and the aphasia all resolved after treatment with antibiotics and valproate. Because these discharges were associated with a reversible neurologic deficit and time-locked to a focal movement, they were classified as an ictal pattern.
Pseudoperiodic generalized epileptiform discharges Pseudoperiodic generalized epileptiform discharges (GPEDs) in a 67-year-old patient after cardiac arrest. Some authors would refer to these discharges as bilateral pseudoperiodic epileptiform discharges (BiPEDs).
These GPEDS were recorded in a 17-year-old with su These GPEDS were recorded in a 17-year-old with subacute sclerosing panencephalitis (SSPE). The patient presented with a slowly progressive encephalopathy and myoclonic jerks when awake. When GPEDs are present in SSPE, they typically repeat at a relatively low frequency and have a complex morphology. During a single recording, the morphology and repetition rate of the discharges are often strikingly stereotyped. When myoclonic jerks are present, they are time-locked to the periodic discharges.
A burst-suppression pattern, a species of GPEDs, r A burst-suppression pattern, a species of GPEDs, recorded after prolonged cardiac arrest. Mixed frequency, low-amplitude bursts of variable morphology are separated by periods of profound background attenuation.

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