Multiple independent spike foci and epilepsy, with special reference to a new epileptic syndrome of “severe epilepsy with multiple independent spike foci”

BackgroundMarkand and Blume first realized the specificity of the EEG pattern of multiple independent spike foci (MISF) in the late 1970s; its close relation with hypsarrhythmia and slow spike-waves, extensive bilateral brain lesion, and intractable seizures. But they did not recognize it as an epileptic syndrome. On the other hand, the authors had been taken notice of severe epilepsy with MISF (SE-MISF) as a peculiar clinico-electrical entity showing “generalized seizures”, and pointed out its close relation to Lennox–Gastaut syndrome (LGS) from the long-term follow-up of LGS.Summary pointsSE-MISF is characterized by (1) interictal EEG showing multiple independent spike foci (three or more foci in both hemisphere, i.e. at least one in each hemisphere) and diffuse slowing of the background activity. Diffuse epileptic discharges are rare. (2) The main seizure type is frequent generalized minor seizures, often tonic spasms. (3) Mutual transition is often observed between the age-dependent epileptic encephalopathies, i.e. Ohtahara syndrome, West syndrome and LGS. (4) The age at epilepsy onset is early, but the onset of SE-MISF is variable. (5) It is often associated with mental retardation and neurological abnormalities, usually severe. (6) Etiology is variable and largely nonspecific, including prenatal, perinatal, and postnatal cerebral pathologies. (7) Prognoses for seizures and psychomotor development are poor. Seizures are very intractable and may cause psychomotor deterioration.ConclusionSE-MISF may be classified into symptomatic generalized epilepsy, namely a diffuse encephalopathy with mutual transition between other age-dependent epileptic encephalopathies. This characteristic entity may be acknowledged as a new epileptic syndrome.