Cognitive performance in functional seizures compared with epilepsy and healthy controls: a systematic review and meta analysis.

Background: Cognition is a core component of functional seizures, but the literature on cognition in this disorder has been heterogeneous, with no clear unifying profile emerging from individual studies. The aim of this study was to do a systematic review and meta-analysis of cognitive performance in adults with functional seizures compared with epilepsy (including left temporal lobe epilepsy) and compared with healthy non-seizure cohorts.

Methods: In this systematic review and meta-analysis, starting Feb 6, 2023, replicated and updated on Oct 31, 2023, a medical librarian searched MEDLINE, Embase, PsycINFO, and Web of Science. Inclusion criteria were full reports documenting raw or standardised cognitive test data in adults with functional seizures compared with adults with epilepsy, prospectively recruited healthy comparisons, or published norms. Grey literature was retained and there were no language or date restrictions. We excluded studies only reporting on mixed functional seizures and epilepsy, or mixed functional neurological samples, with no pure functional seizures group. Risk of bias was evaluated using a modified version of the Newcastle-Ottawa Scale. People with lived experiences were not involved in the design or execution of this study. This study is registered as CRD42023392385 in PROSPERO.

Findings: Of 3834 records initially identified, 84 articles were retained, including 8654 participants (functional seizures 4193, epilepsy 3638, and healthy comparisons 823). Mean age was 36 years (SD 12) for functional seizures, 36 years (12) for epilepsy, and 34 years (10) for healthy comparisons, and the proportion of women per group was 72% (range 18-100) for functional seizures, 59% (range 15-100) for epilepsy, and 69% (range 34-100) for healthy comparisons. Data on race or ethnicity were rarely reported in the individual studies. Risk of bias was moderate. Cognitive performance was better in people with functional seizures than those with epilepsy (Hedges' g=0·17 [95% CI 0·10-0·25)], p<0·0001), with moderate-to-high heterogeneity (Q[56]=128·91, p=0·0001, I²=57%). The functional seizures group performed better than the epilepsy group on global cognition and intelligence quotient (g=0·15 [0·02-0·28], p=0·022) and language (g=0·28 [0·14-0·43], p=0·0001), but not other cognitive domains. A larger effect was noted in language tests when comparing functional seizures with left temporal lobe epilepsy (k=5; g=0·51 [0·10 to 0·91], p=0·015). The functional seizures group underperformed relative to healthy comparisons (g=-0·61 [-0·78 to -0·44], p<0·0001), with significant differences in all cognitive domains. Meta regressions examining effects of multiple covariates on global cognition were not significant.

Interpretation: Patients with functional seizures have widespread cognitive impairments that are likely to be clinically meaningful on the basis of moderate effect sizes in multiple domains. These deficits might be slightly less severe than those seen in many patients with epilepsy but nevertheless argue for consideration of clinical assessment and treatment.

Funding: Department of Veterans Affairs, Veterans Health Administration.