Exploring the interplay between depressive symptoms and seizure outcomes: A single-centre study of drug-resistant epilepsy patients treated with vagus nerve stimulation

Abstract

Background: Vagus nerve stimulation (VNS) is a safe and effective treatment option for patients with drug-resistant epilepsy (DRE) and for those with treatment-resistant depression. VNS can lead to the amelioration of depressive symptoms in patients with DRE, independent of its impact on seizure control. However, the relationship between depressive symptoms and seizure outcomes in patients receiving VNS therapy remains uncertain. Objective: This study aimed to assess whether the presence or absence of depressive symptoms influences seizure outcomes in patients with DRE treated with VNS. Methods: This follow-up study included 51 consecutive adult DRE patients treated with VNS at the Neurology Outpatient Clinic at Tampere University Hospital. All patients underwent a psychiatric evaluation before VNS at baseline (pre-implantation). The severity of depressive symptoms was assessed using the Beck Depression Inventory-1A (BDI) at baseline and repeatedly throughout the follow-up period. We categorized patients into two groups based on the presence or absence of depressive symptoms, as determined by their BDI scores at baseline and during the follow-up after VNS implantation: i) patients with depressive symptoms (PWE + DS), with a BDI score > 12 at least once either at baseline or during the follow-up, and ii) patients without depressive symptoms (PWE - DS), with all BDI scores ≤ 12. The primary seizure outcome measure was the number of patients with > 50 % seizure reduction (responders) for their predominant seizure type. Results: At baseline, psychiatric comorbidities were diagnosed in 29.4 % of patients, and the average baseline BDI score was 7.0 (median 5.0, range 0–41). PWE + DS comprised 41.2 % and PWE - DS 58.8 % of the study population. The median duration of follow-up was 39 months (range 6–102 months). The overall responder rate was 52.1 % for the predominant seizure type, with significantly more responders in the PWE + DS group than in the PWE - DS group (73.7 % vs. 37.9 %, p = 0.027). Among the 11 patients whose predominant seizure type was focal to bilateral tonic-clonic seizures (FBTCS), 81.8 % were responders, and 72.8 % achieved seizure freedom for this seizure type. Conclusion: Our study indicates that DRE patients with depressive symptoms respond better to VNS therapy for their predominant seizure type than those without depressive symptoms. This unexpected finding may be explained by the shared neurobiological background of seizures and depressive symptoms, potentially influenced by VNS treatment. Patients with FBTCS as their predominant seizure type achieved the most favourable outcomes. Further investigations in a larger cohort of DRE patients with depressive symptoms are warranted to validate our results.