Cryptogenic Late‐Onset Epileptic Spasms or Late Infantile Epileptogenic Encephalopathy?

Dear Editors: We recently cataloged our experience with the electro-clinical characterization of seizures in infants (Korff and Nordli, 2006) and noted a group of infants with unique clinical and electrographic characteristics. These infants had seizures after 12 months of age, with a brief tonic or myoclonic onset, followed by behavioral arrest. They all had developmental delay and distinctive EEG characteristics. Most of them had symptomatic etiology. We could not easily place these infants into either West syndrome or Lennox-Gastaut syndrome and suspected that we were dealing with an as-yet undescribed syndrome. We read with great interest the article by Eisermann et al., published in this journal in June, 2006 (Eisermann et al., 2006), and would like to briefly share our experience. Ten patients were identified at Children's Memorial Hospital Epilepsy Center. We present their features in tabular form for ready reference in Table 1. On review, it is apparent that there were many similar features between our patients and those of Eisermann et al. (Eisermann et al., 2006). The seizures in our patients were often characterized by a sudden myoclonic or brief tonic event, evident on EMG and video review. The tonic phase was brief, usually only a few seconds and was followed by a subtle clinical feature like behavioral arrest, slight eye version, a "dazed look" or a gentle relaxation of body tone (a "sinking appearance" as described by one parent). The seizures were accompanied by a sudden electrodecrement sometimes with very fast 20–25 Hz activity (Fig. 1), but there was a conspicuous absence of the prominent 10 Hz discharges seen in Lennox-Gastaut Syndrome. The seizures usually lasted less than 10 seconds, and could occur in groupings. They usually did not occur in sleep. Seizure. Sudden myoclonic event, and tonic phase accompanied by a sudden electrodecrement with 20-25 Hz activity. Like Eisermann et al. (Eisermann et al., 2006), we found that the interictal EEGs did not reveal slow spike-wave discharges, but showed epileptiform discharges, maximal in the posterior regions (Fig. 2). In many patients, these were nearly continual. None of our patients had hypsarhythmia. Interictal EEG: epileptiform discharges, maximal in the posterior regions. However, there were some apparent differences between our patients and those described by Eisermann et al. (Eisermann et al., 2006). To begin with, we did not consider the seizures to be truly spasms for several reasons: 1. Our patients did not show the characteristic diamond shaped EMG correlate during the event; 2. Clinically, the event had either a brief myoclonia, a shrug, or brief tonic posture, and did not precisely resemble an epileptic spasm; 3. the seizures usually did not cluster with the typical periodicity that is often seen with spasms. Instead, the clusters or groupings of seizures had irregular time intervals between each individual event. Secondly, all of our patients had probable or known symptomatic etiologies. The etiology was known is 7/10 cases and two of the others had pre-existing neurological abnormalities prior to the development of seizures. Thirdly, the seizures did not tend to occur during sleep, the interictal EEG features were sometimes slightly discontinuous during sleep, and the abrupt cessation of spiking was often a valuable clinical tool to the appearance of the seizures. We agree that these characteristics are clearly distinct from West syndrome and Lennox-Gastaut syndrome. We also agree that it most likely lies along a developmental spectrum including the aforementioned syndromes and the early epileptogenic encephalopathies (early infantile epileptogenic encephalopathy and early myoclonic epilepsy). Considering this, we propose the term late infantile epileptogenic encephalopathy (LIEE) for this entity.