Objectives To identify, describe, and characterize functional seizure mimics by analyzing patients referred with a putative functional seizure diagnosis that following video telemetry EEG (VT-EEG), received an alternate diagnosis. In addition, identify the proportion of patients who had habitual events captured that had this revision.

Background Making a diagnosis of functional seizures from description alone can prove challenging as they share several features with epileptic seizures. The misdiagnosis of functional seizures as epileptic has previously been described in the literature.¹ However, little is known on the reverse.

Methods The reports of VT-EEGs performed on patients admitted to the Chalfont Centre for Epilepsy between 2019 and 2022 were reviewed. Recordings that did not capture habitual events were excluded. The VT-EEG report, referral letters, and pre-admission clinic letters were reviewed to identify the pre-VT-EEG impression. These were categorised as epileptic, functional, unclear, or both. Subsequently, the VT-EEG reports were categorised based on the VT-EEG findings of the habitual event as epileptic, functional, or an alternative diagnosis. Those seizures that had a pre-VTEEG impression of functional and a post-VT-EEG diagnosis of epileptic, or other miscellaneous conditions, were analysed to identify clinically relevant features that favour an alternate diagnosis. In some cases, these features were used to localize seizure foci

Results There were 444 VT-EEG reports where habitual events were recorded. Approximately 5% of these were of those with functional seizures who had their diagnosis revised. Several groups could be identified in those whose diagnoses were amended. The largest group were of frontal lobe seizures with bizarre semiology. In another group, no ictal abnormalities were present but stereotyped seizures arose during EEG defined sleep. Others included: patients with insular epilepsy and predominant autonomic features; patients with absence seizures; patients with brief epileptic seizures followed by functional overlay or elaboration; and patients with a dual diagnosis whose epileptic seizures were revealed on drug reduction.

Conclusion In patients referred to a tertiary epilepsy unit, the majority of patients retained their diagnosis or changed from epileptic to functional. However, in a small minority of cases, seizures previously diagnosed as functional were reclassified as epileptic or an alternative diagnosis. It is clinically important to be aware of these mimics.

Reference

1. Lanzillotti AI, Sarudiansky M, Lombardi NR, Korman GP, D Alessio L. Updated review on the diagnosis and primary management of psychogenic nonepileptic seizure disorders. Neuropsychiatr Dis Treat. 2021;17:1825–1838. Published 2021 Jun 4. doi:10.2147/NDT.S286710