Lateralized Periodic Discharges!

The discharges are comprised of a variety of waveforms including periodically recurring paroxysmal discharges of spikes, spike waves, sharp waves, and theta or delta slow waves or a mixture of these waves. Periodic discharges are usually of high amplitude, in the range of 100 to 300μV, and may occur in a focal or lateralized, periodic lateralized epileptiform discharges (PLEDs/LPDs). The waveforms can arise from one hemisphere or a restricted area within one hemisphere. The discharges may be repeated as fast as 0.5-2/s or as slow as 10/min.

Subacute sclerosing panencephalitis, Creutzfeldt–Jakob disease, herpes simplex encephalitis, severe cerebral anoxia, infectious mononucleosis, Rasmussen encephalitis, and acute or severe cerebral infarcts (ischemic or hemorrhagic), lesions, and CNS diseases are some conditions often associated with periodic discharges. The most common etiology is acute cerebral infarct, especially of the watershed type. The second most common etiology is herpes simplex (HSV1) encephalitis. HSV1 infection has a preference to involve the temporal lobe or frontotemporal region.

Recently, this pattern has also been reported in posterior reversible encephalopathy syndrome (PRES), alcohol withdrawal, and neurosyphilis. PLDs may also occur acutely after unilateral seizures. They generally disappear gradually over days to weeks. Background activity is usually abnormal, ranging from slowed to nearly completely suppressed. PLDs are frequently associated with seizures—between 58% and 100% of patients with this pattern have clinical seizures, and a significant minority subsequently develop epilepsy. The discharges generally abate within a few weeks. When seen in association with acute stroke, the mortality rate associated with PLDs is ~30%.