Incidence and classification of new-onset epilepsy and epilepsy syndromes in children in Olmsted County, Minnesota from 1980 to 2004: A population-based study

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Summary

Purpose

To determine the incidence and classification of new-onset epilepsy, as well as the distribution of epilepsy syndromes in a population-based group of children, using the newly proposed Report of the ILAE Commission on Classification and Terminology 2005–2009.

Methods

We identified all children residing in Olmsted County, MN, 1 month through 17 years with newly diagnosed epilepsy from 1980 to 2004. For each patient, epilepsy was classified into mode of onset, etiology, and syndrome or constellation (if present). Incidence rates were calculated overall and also separately for categories of mode of onset and etiology.

Results

The adjusted incidence rate of new-onset epilepsy in children was 44.5 cases per 100,000 persons per year. Incidence rates were highest in the first year of life and diminished with age. Mode of onset was focal in 68%, generalized/bilateral in 23%, spasms in 3% and unknown in 5%. Approximately half of children had an unknown etiology for their epilepsy, and of the remainder, 78 (22%) were genetic and 101 (28%) were structural/metabolic. A specific epilepsy syndrome could be defined at initial diagnosis in 99/359 (28%) children, but only 9/359 (3%) had a defined constellation.

Conclusion

Nearly half of childhood epilepsy is of “unknown” etiology. While a small proportion of this group met criteria for a known epilepsy syndrome, 41% of all childhood epilepsy is of “unknown” cause with no clear syndrome identified. Further work is needed to define more specific etiologies for this group.

Section snippets

Incidence

The reported incidence of new-onset seizures in children has shown considerable variation, depending on inclusion criteria. Some studies have included only children with two or more seizures, whereas others have included all first seizures, febrile seizures or neonatal seizures. A small number of population-based studies have reported on the incidence of new-onset epilepsy in developed countries, with the reported incidence ranging from 33.3 to 82 cases per 100,000 persons per year (Blom et

Case identification

Cases were ascertained by screening of the complete diagnostic indexes of the Rochester Epidemiology Project. These indexes include inpatient diagnoses, as well as diagnoses at the time of outpatient and emergency room visits at all medical care facilities in Olmsted County, MN (Melton, 1996). All charts were screened using a diagnostic rubric which included all seizure and convulsion diagnosis codes, and all identified charts were reviewed by a pediatric epileptologist. We identified all

Results

We identified 359 cases fulfilling criteria for new-onset epilepsy diagnosed over the 25-year period from 1980 to 2004 in children aged 1 month through 17 years. All children except three were seen on at least one occasion by a child neurologist who confirmed the diagnosis of epilepsy. Of the remaining three, two were diagnosed with epilepsy by a general neurologist, and one by a pediatrician. Prophylactic antiepileptic drug therapy was commenced in 339 patients while 20 were never treated.

Discussion

The incidence rate of new-onset epilepsy in our cohort, age- and sex-standardized to the year 2000 U.S. population was 44.5 cases per 100,000 persons per year. This rate is consistent with incidence of epilepsy rates of 33.3–82 cases per 100,000 reported in other population-based studies (Adelow et al., 2009, Blom et al., 1978, Camfield et al., 1996, Cavazzuti, 1980, Christensen et al., 2007, Doose and Sitepu, 1983, Freitag et al., 2001, Hauser et al., 1993, Larsson and Eeg-Olofsson, 2006,

Conflict of interest

None of the authors has any conflict of interest to disclose.

Acknowledgements

This study was supported by a CR20 Research award from the Mayo Foundation, and made possible by the Rochester Epidemiology Project (R01 Grant # R01-AG034676 (Dr. W.A. Rocca PI).

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