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To establish the risk of subsequent intractable epilepsy after ≥2, ≥5, and ≥10 years of remission in childhood-onset epilepsy.

From the Nova Scotia childhood-onset epilepsy population-based cohort patients with all types of epilepsy were selected with ≥20 years follow-up from seizure onset (incidence cases). Children with childhood absence epilepsy were excluded. The rate of subsequent intractable epilepsy was then studied for patients with ≥5 years remission on or off AED treatment and compared with the rate for those with ≥2 and ≥10 years of remission.

Three hundred eighty-eight eligible patients had ≥20 years follow-up (average 27.7 ± (standard deviation) 4 years) until they were an average of 34 ± 6.5 years of age. Overall, 297 (77%) had a period of ≥5 years of seizure freedom (average 21.2 ± 8 years), with 90% of these remissions continuing to the end of follow-up. Seizures recurred in 31 (10%) and were intractable in 7 (2%). For the 332 with a remission of ≥2 years seizure-free, 6.9% subsequently developed intractable epilepsy (p = 0.001). For the 260 with ≥10 years remission, 0.78% subsequently developed intractable epilepsy (p = 0.25 compared with ≥5 years remission).

Even after ≥5 or ≥10 years of seizure freedom, childhood-onset epilepsy may reappear and be intractable. The risk is fortunately small, but for most patients it is not possible to guarantee a permanent remission.