• The term periodic lateralized epileptiform
discharges (PLEDs), first coined by Chatrian
and colleagues in 1964, is a peculiar
electroencephalogram (EEG) pattern
consisting of unilateral and focal spikes or
sharp wave complexes that appear
periodically, usually at the rate of 1~2 s.
• Classically triphasic with a sharply contoured
wave followed by a slow wave.
• Incidence of 0.4% to 1%
• Usually a singular focus – PLED’s
• Duration is between 100 to 300 ms
• Amplitude is 100 to 300mV
• It is the conserved recurrence pattern that is
more important than morphology.
• The regularity may vary
– Can be highly regular
– With out any set interval.
• Recurrence frequency commonly fall in the
range of one transient every 0.5 to 4 sec
– 2 sec interval is mc
• Low amplitude slow activity separates PLEDs.
PLEDs or ECG?
• Both have similar morphology and periodicity.
• Simultaneous ECG recording helps.
• PLEDs not as regular as ECG.
• ECG may be unilateral or bilateral
• PLEDs are not bilateraly synchronous.
• BiPED – large frontal fields.
• ECG – temporal region.
• ECG usually 1Hz.
• PLEDs can be differentiated from inter ictal
discharges by periodicity.
• IEDs can periodically recur but interval varies
and occur only sporadically.
• Indicated focal pathology that is acute or sub
• May indicate a cortical involvement and co
existing metabolic abnormality.
• Over all significance is same in children and
• 80% cases there will be a co localized focal
• PLEDs usually lasts day to weeks.
– Rarely years.
• Cortical strokes (50%)
– Embolism, watershed infarcts
• Tumors and cerebral infections(20%)
• Prion diseases, extra-axial
• Rare causes:
– Alzheimer's ds
– Mitochondrial ds
– Intoxication with
baclofen, lithium, levodopa, ifosfamide.
– Trauma with out subsequent hemorrhage.
• PLEDs indicate clinically significant risk for
• Seizure occur in up to 80% of patients with
– Focal motor seizure MC
• 20% with PLEDs are comatosed and 80% will
have impaired consciousness.
• Among infections HSE is the MC.
• Most HSE shoes PLEDs at some point of time.
• MC with in a week of onset of symptoms.
• Disappears by 2 weeks after the onset.
• PLEDs due to HSE is almost always centered over
one or both temporal lobes.
• When B/L are synchronous and time locked.
– Interval 1.5 to 2.5 sec
• Inter discharge intervel almost always 1 to 5 sec.
• Other viruses producing temporal PLEDs:
influenza B, LaCrosse.
• CJD is the MC prion disease producing PLEDs.
– Helps to differentiate CJD from other dementias.
– 67 – 100% CJD will have PLEDs.
– Recur every 0.5 to 2 sec
– Usually hemispheric with focal predominance
when they first manifest.
– Present only during wakefulness.
– Onset after several months of onset of clinical ds.
– Evolve to BiPED as disease progress and
• Reiher et al. (1991) described the brief and
low amplitude focal stereotyped rhythmic
discharges (RDs) closely associated in
temporal and spatial distributions to higher
amplitude interictal epileptiform discharges.
• They subdivided PLEDs into two categories:
• (1) PLEDs plus- associated with RDs and
• (2) PLEDs proper-not associated with RD.
• PLEDs proper were subdivided into PLEDs of
classes 1, 2, and 3
– Based on the metronomicity of the periodicity.
• PLEDs plus could be subdivided into PLEDs of
classes 4 and 5.
– Based on the duration of RDs