Clinical characteristics and semiological pitfalls in patients with focal epilepsy and functional/dissociative seizures: A comparative analysis of correct and incorrect initial diagnoses

Both epilepsy and functional/dissociative seizures (FDS) can present with a wide variety of event manifestations which can appear similar in nature and contribute to misdiagnosis. Whereas many studies have addressed the misdiagnosis of FDS as epilepsy, research into the inverse, where epilepsy is mistaken for a functional disorder, remains limited. Accurate differentiation is vital, because management differs greatly, ranging from antiseizure medications and surgery to specialized mental health interventions.

A retrospective review was conducted of patients undergoing video-electroencephalographic monitoring (VEM) at a level 4 advanced epilepsy center between 2015 and 2023. VEM reports rather than video were reviewed. Patients were categorized into three primary groups: correctly diagnosed focal epilepsy, correctly diagnosed FDS, and misdiagnosed epilepsy (patients initially diagnosed with FDS but confirmed to have epileptic seizures). A fourth group of cases with FDS that were misdiagnosed as epilepsy were excluded.

Epilepsy cases that were misdiagnosed as FDS represented 6% of the total cohort. Fifty percent (n = 13) were male, and the mean age was 33.3 (range = 10-62). Compared to correctly diagnosed epilepsy, the misdiagnosed cases were significantly more likely to have semiological features, consisting of complex motor movements (p = .0009), hyperkinetic activity (p = .0095), and affective symptoms like fear (p = .0001). Notably, frontal lobe epilepsy was proportionally more common in misdiagnosed cases. In contrast, events in cases with correctly diagnosed FDS were characterized by unresponsiveness (p = .0001), hypotonia (p = .0001), and eye closure (p = .019), alongside prolonged duration (p = .0001) and fluctuating semiology (p = .0001). These features were almost entirely absent in the misdiagnosed group. FDS cases also had a significantly higher number of distinct event types but fewer semiological features per event (p = .03). Lateralizing signs were also an indicator of an epilepsy diagnosis, appearing in 58% of misdiagnosed cases compared to only 17% of FDS cases (p < .0001).

Sole reliance on individual signs of FDS can lead to diagnostic errors, particularly in frontal lobe epilepsy. To improve diagnostic certainty, clinicians should analyze the temporal evolution of semiology over isolated motor manifestations. When hyperkinetic or affective symptoms are present, a thorough clinical history and assessment of the temporal evolution of semiology should improve diagnostic certainty and reduce the chances of misdiagnosis.