Antidepressant effect of vagal nerve stimulation in epilepsy patients: a systematic review

Background: Vagal nerve stimulation (VNS) is an effective palliative therapy in drug-resistant epileptic patients and is also approved as a therapy for treatment-resistant depression. Depression is a frequent comorbidity in epilepsy and it affects the quality of life of patients more than the seizure frequency itself. The aim of this systematic review is to analyze the available literature about the VNS effect on depressive symptoms in epileptic patients. Material and methods: A comprehensive search of PubMed, Medline, Scopus, and Google Scholar was performed, and results were included up to January 2020. All studies concerning depressive symptom assessment in epileptic patients treated with VNS were included. Results: Nine studies were included because they fulfilled inclusion criteria. Six out of nine papers reported a positive effect of VNS on depressive symptoms. Eight out of nine studies did not find any correlation between seizure reduction and depressive symptom amelioration, as induced by VNS. Clinical scales for depression, drug regimens, and age of patients were broadly different among the examined studies. Conclusions: Reviewed studies strongly suggest that VNS ameliorates depressive symptoms in drug-resistant epileptic patients and that the VNS effect on depression is uncorrelated to seizure response. However, more rigorous studies addressing this issue are encouraged.