Durability of antidepressant response to vagus nerve stimulation (VNS).

This study characterized the durability of improvement in patients who responded early or late while receiving vagus nerve stimulation (VNS). In both a pilot and pivotal study, patients were identified who had at least a 50% reduction in symptom scores 3 months (early responders) or 12 months (late responders) after starting VNS. Probabilities were determined for maintenance of response at 12-month and 24-month time-points. Consistency of improvement throughout the 24-month study period was evaluated, testing for change in serial depression ratings. In the pilot study, 30.5%, 23.7% and 45.8% were early responders, later responders, and non-responders, respectively. These rates were 14.6%, 19.5%, and 65.9% in the pivotal trial. The potential confound of alterations in antidepressant treatment was examined in the pivotal trial. In the pilot study, 72.2% and 61.1% of early responders (n=18) were responders at 12 and 24 months, respectively; 78.8% of late responders (n=14) were responders at 24 months. In the pivotal trial, of early responders (n=30), 63.3% and 76.7% maintained response at 12 and 24 months, respectively; of late responders (n=40), 65.0% maintained response at 24 months. Early and late responders had fewer changes in medication than non-responders across the pivotal study period. In both studies, analyses of serial depression ratings showed stable improvement in early and late responders. These samples had exceptional levels of chronicity and treatment resistance. Yet patients who showed substantial clinical benefit maintained the improvement at remarkably high rates. This durability of benefit was not attributable to alterations in other treatments.

VNS therapy in treatment-resistant depression: clinical evidence and putative neurobiological mechanisms.

Currently available therapeutic interventions for treatment-resistant depression, including switch, combination, and augmentation strategies, are less than ideal. Observations of mood elevation during vagus nerve stimulation (VNS) therapy for pharmacoresistant epilepsy suggested a role for VNS therapy in refractory major depression and prompted clinical investigation of this neurostimulation modality. The VNS Therapy System has been available for treatment of pharmacoresistant epilepsy since 1997 and was approved by the US Food and Drug Administration for treatment-resistant depression in July, 2005. The physiology of the vagus nerve, mechanics of the VNS Therapy System, and efficacy and safety in pharmacoresistant epilepsy are reviewed. Promising results of VNS therapy for treatment-resistant depression have been forthcoming from both acute and long-term studies, evidenced in part by progressive improvements in depression rating scale scores during the 1st year of treatment with maintenance of response thereafter. VNS therapy is well tolerated in patients with either pharmacoresistant epilepsy or treatment-resistant depression. As in epilepsy, the mechanisms of VNS therapy of treatment-resistant depression are incompletely understood. However, evidence from neuroimaging and other studies suggests that VNS therapy acts via innervation of the nucleus tractus solitarius, with secondary projections to limbic and cortical structures that are involved in mood regulation, including brainstem regions that contain serotonergic (raphe nucleus) and noradrenergic (locus ceruleus) perikarya that project to the forebrain. Mechanisms that mediate the beneficial effects of VNS therapy for treatment-resistant depression remain obscure. Suggestions for future research directions are described.

Vagus nerve stimulation for treatment-resistant depression: a randomized, controlled acute phase trial.

BACKGROUND: Vagus nerve stimulation (VNS) alters both concentrations of neurotransmitters or their metabolites and functional activity of central nervous system regions dysregulated in mood disorders. An open trial has suggested efficacy. METHODS: This 10-week, acute, randomized, controlled, masked trial compared adjunctive VNS with sham treatment in 235 outpatients with nonpsychotic major depressive disorder (n = 210) or nonpsychotic, depressed phase, bipolar disorder (n = 25). In the current episode, participants had not responded adequately to between two and six research-qualified medication trials. A two-week, single-blind recovery period (no stimulation) and then 10 weeks of masked active or sham VNS followed implantation. Medications were kept stable. Primary efficacy outcome among 222 evaluable participants was based on response rates (>/=50% reduction from baseline on the 24-item Hamilton Rating Scale for Depression [HRSD(24)]). RESULTS: At 10-weeks, HRSD(24) response rates were 15.2% for the active (n = 112) and 10.0% for the sham (n = 110) groups (p = .251, last observation carried forward [LOCF]). Response rates with a secondary outcome, the Inventory of Depressive Symptomatology - Self-Report (IDS-SR(30)), were 17.0% (active) and 7.3% (sham) (p = .032, LOCF). VNS was well tolerated; 1% (3/235) left the study because of adverse events. CONCLUSIONS: This study did not yield definitive evidence of short-term efficacy for adjunctive VNS in treatment-resistant depression.

Effects of 12 months of vagus nerve stimulation in treatment-resistant depression: a naturalistic study.

BACKGROUND: The need for effective, long-term treatment for recurrent or chronic, treatment-resistant depression is well established. METHODS: This naturalistic follow-up describes outpatients with nonpsychotic major depressive (n = 185) or bipolar (I or II) disorder, depressed phase (n = 20) who initially received 10 weeks of active (n = 110) or sham vagus nerve stimulation (VNS) (n = 95). The initial active group received another 9 months, while the initial sham group received 12 months of VNS. Participants received antidepressant treatments and VNS, both of which could be adjusted. RESULTS: The primary analysis (repeated measures linear regression) revealed a significant reduction in 24-item Hamilton Rating Scale for Depression (HRSD(24)) scores (average improvement, .45 points [SE = .05] per month (p < .001). At exit, HRSD(24) response rate was 27.2% (55/202); remission rate (HRSD(24) < or = 9) was 15.8% (32/202). Montgomery Asberg Depression Rating Scale (28.2% [57/202]) and Clinical Global Impression-Improvement (34.0% [68/200]) showed similar response rates. Voice alteration, dyspnea, and neck pain were the most frequently reported adverse events. CONCLUSIONS: These 1-year open trial data found VNS to be well tolerated, suggesting a potential long-term, growing benefit in treatment-resistant depression, albeit in the context of changes in depression treatments. Comparative long-term data are needed to determine whether these benefits can be attributed to VNS.

A one-year comparison of vagus nerve stimulation with treatment as usual for treatment-resistant depression.

BACKGROUND: Previous reports have described the effects of vagus nerve stimulation plus treatment as usual (VNS+TAU) during open trials of patients with treatment-resistant depression (TRD). To better understand these effects on long-term outcome, we compared 12-month VNS+TAU outcomes with those of a comparable TRD group. METHODS: Admission criteria were similar for those receiving VNS+TAU (n = 205) or only TAU (n = 124). In the primary analysis, repeated-measures linear regression was used to compare the VNS+TAU group (monthly data) with the TAU group (quarterly data) according to scores of the 30-item Inventory of Depressive Symptomatology-Self-Report (IDS-SR(30)). RESULTS: The two groups had similar baseline demographic data, psychiatric and treatment histories, and degrees of treatment resistance, except that more TAU participants had at least 10 prior major depressive episodes, and the VNS+TAU group had more electroconvulsive therapy before study entry. Vagus nerve stimulation plus treatment as usual was associated with greater improvement per month in IDS-SR(30) than TAU across 12 months (p < .001). Response rates according to the 24-item Hamilton Rating Scale for Depression (last observation carried forward) at 12 months were 27% for VNS+TAU and 13% for TAU (p < .011). Both groups received similar TAU (drugs and electroconvulsive therapy) during follow-up. CONCLUSIONS: This comparison of two similar but nonrandomized TRD groups showed that VNS+TAU was associated with a greater antidepressant benefit over 12 months.