Early-infantile epileptic encephalopathy with suppression-bursts, Ohtahara syndrome; its overview referring to our 16 cases

Ohtahara syndrome (OS) is characterized by frequent tonic spasms, with or without clustering, of early onset within a few months of life, and a suppression-burst (S-B) pattern in electroencephalography (EEG). Tonic spasms occur in not only waking but also sleeping state in most cases. Partial seizures are observed in about one-third of cases. Brain imagings reveal structural abnormalities including malformations, notably asymmetric lesions in most cases. S-B pattern is persistently observed regardless of circadian cycle. Bursts of 1–3 s duration alternate with nearly flat suppression phase of 2–5 s at an approximately regular rate; 5–10 s of burst–burst interval. Some asymmetry in S-B is noted in about two-thirds of cases. Ictal EEG of tonic spasms shows principally desynchronization with or without initial rapid activity. Tonic spasms appear concomitant with bursts. Characteristic age-dependent evolution from OS to West syndrome (WS) in many cases, and further from WS to Lennox–Gastaut syndrome (LGS) in some, proceed concomitantly with EEG transition from S-B to hypsarrhythmia at around age 3–6 months, and further from hypsarrhythmia to diffuse slow spike-waves at around age 1. Under the inclusive concept of the age-dependent epileptic encephalopathy, OS, WS, and LGS have common characteristics such as age preference, frequent minor generalized seizures, and continuous massive epileptic EEG abnormality. Mutual transition suggests the same pathophysiology among three syndromes and the age factor should be considered as the common denominator responsible for the manifestation of each of their own specific clinico-electrical features. Namely, these syndromes may be the age-specific epileptic reaction to various non-specific exogenous brain insults, acting at the specific developmental stages.