Neurostimulatory therapeutics in management of treatment-resistant depression with focus on deep brain stimulation

Deep brain stimulation for treatment-resistant depression: an integrative review of preclinical and clinical findings and translational implications

Although deep brain stimulation (DBS) is an established treatment choice for Parkinson's disease (PD), essential tremor and movement disorders, its effectiveness for the management of treatment-resistant depression (TRD) remains unclear. Herein, we conducted an integrative review on major neuroanatomical targets of DBS pursued for the treatment of intractable TRD. The aim of this review article is to provide a critical discussion of possible underlying mechanisms for DBS-generated antidepressant effects identified in preclinical studies and clinical trials, and to determine which brain target(s) elicited the most promising outcomes considering acute and maintenance treatment of TRD. Major electronic databases were searched to identify preclinical and clinical studies that have investigated the effects of DBS on depression-related outcomes. Overall, 92 references met inclusion criteria, and have evaluated six unique DBS targets namely the subcallosal cingulate gyrus (SCG), nucleus accumbens (NAc), ventral capsule/ventral striatum or anterior limb of internal capsule (ALIC), medial forebrain bundle (MFB), lateral habenula (LHb) and inferior thalamic peduncle for the treatment of unrelenting TRD. Electrical stimulation of these pertinent brain regions displayed differential effects on mood transition in patients with TRD. In addition, 47 unique references provided preclinical evidence for putative neurobiological mechanisms underlying antidepressant effects of DBS applied to the ventromedial prefrontal cortex, NAc, MFB, LHb and subthalamic nucleus. Preclinical studies suggest that stimulation parameters and neuroanatomical locations could influence DBS-related antidepressant effects, and also pointed that modulatory effects on monoamine neurotransmitters in target regions or interconnected brain networks following DBS could have a role in the antidepressant effects of DBS. Among several neuromodulatory targets that have been investigated, DBS in the neuroanatomical framework of the SCG, ALIC and MFB yielded more consistent antidepressant response rates in samples with TRD. Nevertheless, more well-designed randomized double-blind, controlled trials are warranted to further assess the efficacy, safety and tolerability of these more promising DBS targets for the management of TRD as therapeutic effects have been inconsistent across some controlled studies.

Neuromodulation therapies and treatment-resistant depression

Background

Patients with treatment-resistant depression (TRD) who showed partial response to pharmacological and psychotherapeutic interventions need a trial of neuromodulation therapies (NTs).

Objective

This paper aims to review evidence-based data on the use of NTs in TRD.

Method

Using keywords and combined-word strategy, multiple computer searches of PubMed, Google Scholar, Quertle(R), and Medline were conducted for retrieving relevant articles published in English-language peer-reviewed journals (2000–2012). Those papers that addressed NTs in TRD were retained for extensive review.

Results

Despite methodological challenges, a range of 30%–93% of TRD patients showed substantial improvement to one of the NTs. One hundred–percent improvement was reported in two single-case studies on deep brain stimulation. Some studies reported no benefits from transcranial direct current stimulation. NTs were reported to have good clinical efficacy, better safety margin, and benign side-effect profile. Data are limited regarding randomized clinical trials, long-term efficacy, and cost-effectiveness of these approaches. Both modified electroconvulsive therapy and magnetic seizure therapy were associated with reversible but disturbing neurocognitive adverse effects. Besides clinical utility, NTs including approaches on the horizon may unlock the biological basis underlying mood disorders including TRD.

Conclusion

NTs are promising in patients with TRD, as the majority of them show good clinical response measured by standardized depression scales. NTs need further technological refinements and optimization together with continuing well-designed studies that recruit larger numbers of participants with TRD.

A primary care focus on the treatment of patients with major depressive disorder

Major depressive disorder (MDD) is a common psychiatric illness affecting nearly 20% of adults in the United States at least once during their lifetime. MDD is frequently diagnosed and treated in the primary care setting. Management of the disease may be complicated by patients and family members feeling stigmatized by the diagnosis and not understanding that depression is a treatable medical illness, which, in turn, fosters low rates of adherence to treatment recommendations. Incomplete or delayed response to treatment, adverse events associated with antidepressants and medical or psychiatric comorbidities also interfere with optimal depression management. This article presents an overview of diagnostic and treatment guidelines for MDD and focuses on challenges encountered by primary care physicians. The role of antidepressant medications, psychotherapy and nonpharmacologic interventions for the treatment of patients with MDD is described, and factors influencing treatment selection, such as adverse event profiles and patient characteristics, are examined.

A primary care focus on the diagnosis and treatment of major depressive disorder in adults

Major depressive disorder (MDD), a highly prevalent psychiatric condition, is encountered in 1 of every 10 to 20 patients seen in the primary care setting. While awareness of MDD has increased, timely and accurate diagnosis and adequate treatment remain formidable challenges. Treatment options for patients with MDD should be individualized according to each patient's clinical and medication history, pharmacologic tolerability profile, and personal preferences, to maximize long-term adherence. The most robust and consistently maintained positive outcomes occur in patients who are administered effective treatment with recommended antidepressant pharmacotherapy, psychotherapy, or a combination of these treatment modalities. This manuscript reviews the epidemiology, biologic and clinical features, diagnosis, and treatment of patients with MDD. A focus is placed on guidelines and strategies that target the achievement of MDD symptom remission. The article also includes details on individualizing treatment selection and novel and emerging therapies. Primary care physicians must be prepared to adjust, substitute, or augment antidepressant treatments to optimize patient response and enhance the chances of achieving remission. Considerations that strongly influence long-term patient adherence, including tolerability and cost, are also reviewed.

Neuromodulation approaches for the treatment of major depression: challenges and recommendations from a working group meeting

The use of neuromodulation as a treatment for major depressive disorder (MDD) has recently attracted renewed interest due to development of other non-pharmacological therapies besides electroconvulsive therapy (ECT) such as transcranial magnetic stimulation (TMS), transcranial direct current stimulation (tDCS), deep brain stimulation (DBS), and vagus nerve stimulation (VNS). METHOD: We convened a working group of researchers to discuss the updates and key challenges of neuromodulation use for the treatment of MDD. RESULTS: The state-of-art of neuromodulation techniques was reviewed and discussed in four sections: [1] epidemiology and pathophysiology of MDD; [2] a comprehensive overview of the neuromodulation techniques; [3] using neuromodulation techniques in MDD associated with non-psychiatric conditions; [4] the main challenges of neuromodulation research and alternatives to overcome them. DISCUSSION: ECT is the first-line treatment for severe depression. TMS and tDCS are strategies with a relative benign profile of side effects; however, while TMS effects are comparable to antidepressant drugs for treating MDD; further research is needed to establish the role of tDCS. DBS and VNS are invasive strategies with a possible role in treatment-resistant depression. In summary, MDD is a chronic and incapacitating condition with a high prevalence; therefore clinicians should consider all the treatment options including invasive and non-invasive neuromodulation approaches.

Evolving refractory major depressive disorder diagnostic and treatment paradigms: toward closed-loop therapeutics

Current antidepressant therapies do not effectively control or cure depressive symptoms. Pharmaceutical therapies altogether fail to address an estimated 4 million Americans who suffer from a recurrent and severe treatment-resistant form of depression known as refractory major depressive disorder. Subjective diagnostic schemes, differing manifestations of the disorder, and antidepressant treatments with limited theoretical bases each contribute to the general lack of therapeutic efficacy and differing levels of treatment resistance in the refractory population. Stimulation-based therapies, such as vagus nerve stimulation, transcranial magnetic stimulation, and deep brain stimulation, are promising treatment alternatives for this treatment-resistant subset of patients, but are plagued with inconsistent reports of efficacy and variable side effects. Many of these problems stem from the unknown mechanisms of depressive disorder pathogenesis, which prevents the development of treatments that target the specific underlying causes of the disorder. Other problems likely arise due to the non-specific stimulation of various limbic and paralimbic structures in an open-loop configuration. This review critically assesses current literature on depressive disorder diagnostic methodologies, treatment schemes, and pathogenesis in order to emphasize the need for more stringent depressive disorder classifications, quantifiable biological markers that are suitable for objective diagnoses, and alternative closed-loop treatment options tailored to well-defined forms of the disorder. A closed-loop neurostimulation device design framework is proposed, utilizing symptom-linked biomarker abnormalities as control points for initiating and terminating a corrective electrical stimulus which is autonomously optimized for correcting the magnitude and direction of observed biomarker abnormality.

Combined administration of the mixture of honokiol and magnolol and ginger oil evokes antidepressant-like synergism in rats

Magnolia bark combined with ginger rhizome is a common drug pair in traditional Chinese prescriptions for the treatment of depression. In the present study, we examined antidepressant-like effects of the mixture of honokiol and magnolol (HMM) from magnolia bark and essential oil from ginger rhizome (OGR) alone and in combination in chronic unpredictable mild stress (CUMS) of rats. Behavioral (sucrose intake, immobility time of forced swimming test) and biochemical parameters [serotonin (5-HT) in prefrontal cortex, hippocampus, and striatum, gastric mucosa cholecystokinin (CCK) and serum gastrin (GAS) levels] were simultaneously examined in the CUMS rats. 20 mg/kg HMM alone, but not OGR, significantly increased sucrose intake and reduced immobility time in the CUMS rats. Moreover, 20 mg/kg HMM and 14 mg/kg OGR in combination exhibited significant synergistic effects on sucrose intake increase and immobility time reduction in the CUMS rats. HMM elevated 5-HT levels in various brain regions, and OGR reduced gastric mucosa CCK and serum GAS levels in the CUMS rats. These results suggested that the synergistic antidepressant-like effects of compatibility of HMM with OGR might be mediated simultaneously by regulation of the serotonergic and gastroenteric system functions. These findings also provided a pharmacological basis for the clinical application of this drug pair of magnolia bark and ginger rhizome in traditional Chinese medicine.

Transcranial direct current stimulation as a therapeutic tool for the treatment of major depression: insights from past and recent clinical studies

PURPOSE OF REVIEW

Transcranial direct current stimulation (tDCS) is a noninvasive method of brain stimulation that has been increasingly tested for the treatment of neuropsychiatric disorders. It has useful characteristics, such as low cost, ease of use, reliable sham methodology, and relatively powerful effects on cortical excitability. Because of its potential to modulate cortical excitability noninvasively, tDCS has been tested for the treatment of depression for several decades. Therefore, we reviewed evidence on the use of tDCS for major depression examining evidence from past and recent tDCS studies. We also briefly compared tDCS with other techniques of neuromodulation, namely deep brain stimulation, vagal nerve stimulation, and transcranial magnetic stimulation; and suggest future directions for the use of tDCS in major depression.

RECENT FINDINGS

Results from past clinical trials testing direct current stimulation as a therapeutic tool had mixed methodology and showed heterogeneous results. Recent studies on tDCS and depression using novel approaches, such as different parameters of stimulation, have improved its neuromodulatory effect thus resulting in larger clinical effects. In fact, two recent small trials have shown that tDCS is associated with significant clinical gains.

SUMMARY

On the basis of these findings there is still not enough evidence to support tDCS as a therapeutic modality for depression. However, findings to date encourage further studies in this area that should explore novel parameters of stimulation. In fact, it appears that current methods of tDCS might not be fully optimized and, in fact, (1) individualized parameters of stimulation, (2) longer stimulation sessions, and (3) methods to focalize tDCS might be useful strategies to provide greater clinical benefits.