Cognition-enhancing effect of vagus nerve stimulation in patients with Alzheimer's disease: a pilot study

BACKGROUND: Vagus nerve stimulation (VNS) is an established treatment method for therapy-refractory epilepsy and, in Europe, for treatment-resistant depression also. Clinical and experimental investigations have also shown positive effects of VNS on cognition in epilepsy and depression. The purpose of the present pilot study was to investigate the effect of VNS on cognition in patients with Alzheimer's disease. METHOD: All the included patients (N = 10) met the National Institute of Neurological and Communicative Disorders and Stroke and the Alzheimer's Disease and Related Disorders Association criteria for the diagnosis of Alzheimer's disease. Before the implantation of the vagus stimulator (NeuroCybernetic Prosthesis), the patients underwent neuropsychological tests (e.g., Alzheimer's Disease Assessment Scale-cognitive subscale [ADAS-cog] and Mini-Mental State Examination [MMSE]), computerized tomography of the brain, medical/neurologic and psychological examinations (status evaluation), and lumbar puncture with investigation of the cerebrospinal fluid. The presence of depressive symptoms was rated using the Montgomery-Asberg Depression Rating Scale. The VNS was initiated 2 weeks after the implantation, and the patients were followed up with regular investigations and tests over 6 months. Response was defined as improvement or absence of impairment in ADAS-cog and MMSE scores after 3 and 6 months. RESULTS: After 3 months of treatment, 7 of 10 patients were responders according to the ADAS-cog (median improvement of 3.0 points), and 9 of 10 patients were responders according to the MMSE (median improvement of 1.5 points). After 6 months of treatment, 7 patients were responders on the ADAS-cog (median improvement of 2.5 points), and 7 patients were responders on the MMSE (median improvement of 2.5 points). VNS was well tolerated, and its side effects were mild and transient. CONCLUSION: The results of this open-label pilot study suggest a positive effect of VNS on cognition in patients with Alzheimer's disease. Further studies are warranted.