Cessation of anti-seizure medications in patients with established functional seizures has been shown to confirm the diagnosis, increase patient satisfaction, and improve seizure outcomes. Published literature reports a wide variation in the rate of comorbid epilepsy, ranging from 10% to 60%. Our goal was to assess how often factors that raise the suspicion of comorbid epilepsy are observed in patients with functional seizures. We also propose diagnostic criteria for comorbid epilepsy, which may help in patient counseling and promote more judicious use of anti-seizure medications.

We included 100 patients with functional seizures (median age 37, interquartile range 28-48; 78% female).  The certainty of comorbid epilepsy was deemed unlikely in 64%, possible in 10%, probable in 13%, clinically established in 2%, and documented in 11%. The most common clinical factor that made comorbid epilepsy "possible" was nocturnal events. Interictal epileptiform discharges resulted in comorbid epilepsy being classified as "probable" in 11% of cases.