Changes in metabolites after treatment with memantine in fibromyalgia. A double-blind randomized controlled trial with magnetic resonance spectroscopy with a 6-month follow-up

Advances in the management of fibromyalgia: what is the state of the art?

INTRODUCTION

Fibromyalgia (FM) is a chronic pain syndrome associated with fatigue, insomnia, dyscognition, and emotional distress. Critical illness mechanisms include central sensitization to nociceptive and non-nociceptive stimuli often resulting in hypersensitivity to all sensory input.

AREAS COVERED

The clinical presentation of FM can vary widely and therefore requires therapies tailored to each patient's set of symptoms. This manuscript examines currently prescribed therapeutic approaches supported by empirical evidence as well as promising novel treatments. Although pharmacological therapy until now has been only moderately effective for FM symptoms, it represents a critical component of every treatment plan.

EXPERT OPINION

Currently approved pharmacological therapies for FM symptoms have limited but proven effectiveness. Novel therapies with cannabinoids and naltrexone appear promising. Recent functional imaging studies of FM have discovered multiple brain network abnormalities that may provide novel targets for mechanism-based therapies. Future treatment approaches, however, need to improve more than clinical pain but also other FM domains like fatigue, insomnia, and distress.

Study protocol for a randomised, double-blinded, placebo-controlled phase III trial examining the add-on efficacy, cost-utility and neurobiological effects of low-dose naltrexone (LDN) in patients with fibromyalgia (INNOVA study)

INTRODUCTION

There is evidence that low-dose naltrexone (LDN; <5.0 mg/day) reduces pain and improves the quality of life of people with fibromyalgia syndrome (FMS). However, no randomised controlled trials with long-term follow-ups have been carried out. The INNOVA study will evaluate the add-on efficacy, safety, cost-utility and neurobiological effects of LDN for reducing pain in patients with FMS, with a 1-year follow-up.

METHODS AND ANALYSIS

A single-site, prospective, randomised, double-blinded, placebo-controlled, parallel design phase III trial will be performed. Eligibility criteria include being adult, having a diagnosis of FMS and experiencing pain of 4 or higher on a 10-point numerical rating scale. Participants will be randomised to a LDN intervention group (4.5 mg/day) or to a placebo control group. Clinical assessments will be performed at baseline (T0), 3 months (T1), 6 months (T2) and 12 months (T3). The primary endpoint will be pain intensity. A sample size of 60 patients per study arm (120 in total), as calculated prior to recruitment for sufficient power, will be monitored between January 2022 and August 2024. Assessment will also include daily ecological momentary evaluations of FMS-related symptoms (eg, pain intensity, fatigue and sleep disturbance), and side effects via ecological momentary assessment through the Pain Monitor app during the first 3 months. Costs and quality-adjusted life years will be also calculated. Half of the participants in each arm will be scanned with MRI at T0 and T1 for changes in brain metabolites related to neuroinflammation and central sensitisation. Inflammatory biomarkers in serum will also be measured.

ETHICS AND DISSEMINATION

This study has been approved by the Ethics Committee of the Fundació Sant Joan de Déu. The results will be actively disseminated through peer-reviewed journals, conference presentations, social media and community engagement activities.

TRIAL REGISTRATION NUMBER

NCT04739995.

Low-Dose Dextromethorphan for the Treatment of Fibromyalgia Pain: Results from a Longitudinal, Single-Blind, Placebo-Controlled Pilot Trial

Objective

Fibromyalgia (FM) is a debilitating chronic pain condition with few treatment options. Central sensitization and neuroinflammation have been forwarded as models of FM pathophysiology, both of which indicate dextromethorphan (DXM) as a potential treatment. DXM is an NMDA-receptor antagonist and microglial modulator with anti-neuroinflammatory properties at low doses. It is available for clinical use but has not been tested as a treatment for FM at low dosages. This study evaluated the effectiveness of DXM in treating FM-associated symptoms.

Methods

In a single-blind, placebo-controlled trial, 14 women meeting the 2010 American College of Rheumatology criteria for FM received a placebo for five weeks, followed by 20 mg DXM for ten weeks, while providing daily symptom reports on a 0–100 scale. Pain and physical activity were the primary and secondary outcomes, respectively. Daily symptom ratings during the last four weeks of placebo were contrasted with ratings during the last four weeks of the active treatment using generalized estimating equations (GEE).

Results

DXM was well tolerated, and treatment adherence was high. Baseline pain was reduced by at least 20% in six participants. Self-reported daily pain and physical activity in the entire cohort were not significantly different between the placebo and DXM conditions, and the primary hypotheses were not supported. Exploratory analyses using the entire placebo and DXM data showed that pain was significantly lower in the DXM condition than in the placebo condition (b=−9.933, p=0.013).

Discussion

A strong clinical effect of DXM was not observed at the 20mg/day dosage.

Metabolite activity in the anterior cingulate cortex during a painful stimulus using functional MRS

To understand neurochemical brain responses to pain, proton magnetic resonance spectroscopy (1H-MRS) is used in humans in vivo to examine various metabolites. Recent MRS investigations have adopted a functional approach, where acquisitions of MRS are performed over time to track task-related changes. Previous studies suggest glutamate is of primary interest, as it may play a role during cortical processing of noxious stimuli. The objective of this study was to examine the metabolic effect (i.e., glutamate) in the anterior cingulate cortex during noxious stimulation using fMRS. The analysis addressed changes in glutamate and glutamate + glutamine (Glx) associated with the onset of pain, and the degree by which fluctuations in metabolites corresponded with continuous pain outcomes. Results suggest healthy participants undergoing tonic noxious stimulation demonstrated increased concentrations of glutamate and Glx at the onset of pain. Subsequent reports of pain were not accompanied by corresponding changes in glutamate of Glx concentrations. An exploratory analysis on sex revealed large effect size changes in glutamate at pain onset in female participants, compared with medium-sized effects in male participants. We propose a role for glutamate in the ACC related to the detection of a noxious stimulus.

Changes in metabolites in the brain of patients with fibromyalgia after treatment with an NMDA receptor antagonist

The aims of this work were to evaluate whether the treatment of patients with fibromyalgia with memantine is associated with significant changes in metabolite concentrations in the brain, and to explore any changes in clinical outcome measures. Magnetic resonance spectroscopy was performed of the right anterior and posterior insula, both hippocampi and the posterior cingulate cortex. Questionnaires on pain, anxiety, depression, global function, quality of life and cognitive impairment were used. Ten patients were studied at baseline and after three months of treatment with memantine. Significant increases were observed in the following areas: N-acetylaspartate (4.47 at baseline vs. 4.71 at three months, p = 0.02) and N-acetylaspartate+N-acetylaspartate glutamate in the left hippocampus (5.89 vs. 5.98; p = 0.007); N-acetylaspartate+N-acetylaspartate glutamate in the right hippocampus (5.31 vs 5.79; p = 0.01) and the anterior insula (7.56 vs. 7.70; p = 0.033); glutamate+glutamine/creatine ratio in the anterior insula (2.03 vs. 2.17; p = 0.022) and the posterior insula (1.77 vs. 2.00; p = 0.004); choline/creatine ratio in the posterior cingulate (0.18 vs. 0.19; p = 0.023); and creatine in the right hippocampus (3.60 vs. 3.85; p = 0.007). At the three-month follow-up, memantine improved cognitive function assessed by the Cognition Mini-Exam (31.50, SD = 2.95 vs. 34.40, SD = 0.6; p = 0.005), depression measured by the Hamilton Depression Scale (7.70, SD = 0.81 vs. 7.56, SD = 0.68; p = 0.042) and severity of illness measured by the Clinical Global Impression severity scale (5.79, SD = 0.96 vs. 5.31, SD = 1.12; p = 0.007). Depression, clinical global impression and cognitive function showed improvement with memantine. Magnetic resonance spectroscopy could be useful in monitoring response to the pharmacological treatment of fibromyalgia.

A systematic review and meta-analysis of memantine for the prevention or treatment of chronic pain

BACKGROUND AND OBJECTIVE

N-methyl-D-aspartate (NMDA) receptors are involved in pain signalling and neuroplasticity. Memantine has been shown to have analgesic properties in pre-clinical and small clinical studies. We conducted a systematic review and meta-analysis to assess the efficacy of memantine to prevent or reduce chronic pain.

DATABASES AND DATA TREATMENT

MEDLINE, EMBASE and CENTRAL databases were searched for comparative trials using memantine, either against placebo or active medications, for chronic pain in adults. Pain relief was considered our primary outcome. Meta-analyses were conducted if outcomes were reported in two or more studies. Outcomes were reported as mean differences (MD) or risk ratios (RR) with 95% confidence intervals (CI). Quality was assessed using the GRADE approach.

RESULTS

Among 454 citations, 15 studies were included with populations predominantly consisting of neuropathic conditions and fibromyalgia. Overall, we observed unclear reporting of randomization and allocation methods, apart from potential for publication bias. Among the 11 studies looking at chronic pain treatment, the difference in end pain score with memantine was not significant: MD = -0.58 units (95% CI -1.31, 0.14); I²  = 82% (low quality). In two surgical studies using memantine for pain prevention, memantine decreased pain intensity: MD = -1.02 units (95% CI -1.38, -0.66); I²  = 0%. Dizziness was significantly more common with memantine: RR = 4.90 (95% CI 1.26, 18.99); I²  = 52% (moderate quality).

CONCLUSION

The current evidence regarding the use of memantine for chronic pain is limited and uncertain. Despite its potential, pain relief achieved in clinical studies is small and is associated with an increase in dizziness.

SIGNIFICANCE

Despite a sound rationale, the benefit of using memantine for chronic pain is unclear. Our systematic review and meta-analysis show that memantine may have the potential to decrease pain. However, it can also increase common adverse effects. Considering the small number of studies with potential for bias and inconclusive evidence, there was low to very low certainty. Hence, no clear recommendations can be made about its routine clinical use until larger and more definitive studies are conducted.

Expanding Role of NMDA Receptor Antagonists in the Management of Pain

Pain management is complex regardless of whether the pain is acute or chronic in nature or non-cancer or cancer related. In addition, relatively few pain pharmacotherapy options with adequate efficacy and safety data currently exist. Consequently, interest in the role of NMDA receptor antagonists as a pharmacological pain management strategy has surfaced. This narrative review provides an overview of the NMDA receptor and elaborates on the pharmacotherapeutic profile and pain management literature findings for the following NMDA receptor antagonists: ketamine, memantine, dextromethorphan, and magnesium. The literature on this topic is characterized by small studies, many of which exhibit methodological flaws. To date, ketamine is the most studied NMDA receptor antagonist for both acute and chronic pain management. Although further research about NMDA receptor antagonists for analgesia is needed and the optimal dosage/administration regimens for these drugs have yet to be determined, ketamine appears to hold the most promise and may be of particular value in the perioperative pain management realm.

Measuring Glutamate Levels in the Brains of Fibromyalgia Patients and a Potential Role for Glutamate in the Pathophysiology of Fibromyalgia Symptoms: A Systematic Review

OBJECTIVES

The aim of this study was to systematically review the literature concerning proton magnetic resonance spectroscopy (H-MRS) measured glutamate levels in specific brain regions of fibromyalgia (FM) patients to determine if there is a correlation between raised glutamate levels and the presentation of FM.

MATERIALS AND METHODS

The electronic databases-MEDLINE, EMBASE Classic+Embase, PsychINFO, Cochrane Database of Systematic Reviews, Cochrane Database of Abstracts of Reviews of Effect, Cochrane Central Register of Controlled Trials-were searched to find original studies that used H-MRS to measure glutamate concentrations in the brains of FM patients.

RESULTS

Nine studies with a total of 482 participants were selected for inclusion in the review. Seven of the 8 studies that investigated an association between cerebral glutamate levels and FM, showed a positive association. Brain regions identified as having increased glutamate levels include the posterior cingulate gyrus, posterior insula, ventrolateral prefrontal cortex, and amygdala. One study reported a decrease in glutamate levels in the hippocampus of FM patients compared with healthy controls. Seven of the 8 studies that analyzed the correlations between cerebral glutamate levels and FM symptoms, found a significant positive correlation.

DISCUSSION

Although the cause of FM remains inconclusive, there is converging data in favor of a dysregulation of pain processing in the central nervous system of FM patients, particularly associated with an increase in cerebral glutamate levels. Furthermore, there is evidence to support an association between increased glutamate levels and an increase in FM symptoms.

An update on emerging drugs for fibromyalgia treatment

INTRODUCTION

Fibromyalgia (FM) is a chronic disorder whose symptoms of pain, fatigue, sleep disturbances and depression have a devastating effect on patients' lives as it limits their ability to engage in everyday working and social activities, and make it difficult to maintain normal relationships with family, friends and employers. None of the currently available drugs are fully effective against the whole spectrum of symptoms. The aim of this narrative review is to summarise the data relating to the new therapeutic options that have become available over the last few years. Areas covered: Increasing efforts by the pharmaceutical industry have led to the introduction of new investigational drugs and new formulations of older drugs, and studies have been carried out in order to investigate the possibility of using drugs that are currently used for other diseases. Expert opinion: Slight improvements in the health of FM patients treated with drugs targeting a range of molecular mechanisms have been observed, but there is still no single drug that is capable of offering substantial efficacy against all of the characteristic symptoms of FM. The identification of new and improved therapies for FM requires consideration of the heterogeneity of the condition, which suggests the existence of different patient subgroups, a relationship between central and peripheral aspects of the pathophysiology, and the need for combined treatment with drugs targeting multiple molecular mechanisms.

Modulation of NMDA Receptor Activity in Fibromyalgia

Activation of the N-methyl-d-aspartate receptor (NMDAR) results in increased sensitivity of spinal cord and brain pathways that process sensory information, particularly those which relate to pain. The NMDAR shows increased activity in fibromyalgia and hence modulation of the NMDAR is a target for therapeutic intervention. A literature review of interventions impacting on the NMDAR shows a number of drugs to be active on the NMDAR mechanism in fibromyalgia patients, with variable clinical effects. Low-dose intravenous ketamine and oral memantine both show clinically useful benefit in fibromyalgia. However, consideration of side-effects, logistics and cost need to be factored into management decisions regarding use of these drugs in this clinical setting. Overall benefits with current NMDAR antagonists appear modest and there is a need for better strategy trials to clarify optimal dose schedules and to delineate potential longer–term adverse events. Further investigation of the role of the NMDAR in fibromyalgia and the effect of other molecules that modulate this receptor appear important to enhance treatment targets in fibromyalgia.

Emerging pharmacological strategies for the treatment of fibromyalgia

Fibromyalgia (FM) has been described as a chronic clinical condition related to multisensory hypersensitivity presenting with a complex of symptoms dominated by chronic widespread pain associated with the existence of a range of co-morbidities, such as fatigue, sleep disturbance, cognitive impairment, anxiety and depression. Current treatments include drugs that target serotonin and noradrenaline levels within the central nervous system, e.g., tricyclic antidepressants, serotonin noradrenaline reuptake inhibitors, and voltage-gated calcium channel subunit ligands, e.g., gabapentin and pregabalin. Investigation of a range of novel targets, such as melatoninergic, cannabinoid, dopamine, NMDA, angiotensin, orexin and opioid receptors, and ion channels, in addition revisiting bioamine modulation and subunits has provided efficacy outcomes that improve the health status of patients with FM. Nevertheless, modest and limited efficacy is often observed reflecting the heterogeneity of FM with existence of subpopulations of patients, the contribution of peripheral and central components to the pathophysiology, and the extensive range of accompanying co-morbidities. The complexity and multidimensional nature of FM is emphasized by the diversity of pharmacological targets gaining interest. Clues to underlying mechanisms which offer themselves as novel and potential targets for new medications are being provided by advances in the understanding of the pathophysiology of FM.

Prefrontal Structure Varies as a Function of Pain Symptoms in Chronic Fatigue Syndrome

BACKGROUND

Chronic fatigue syndrome (CFS) is characterized by severe fatigue persisting for ≥6 months and leading to considerable impairment in daily functioning. Neuroimaging studies of patients with CFS have revealed alterations in prefrontal brain morphology. However, it remains to be determined whether these alterations are specific for fatigue or whether they relate to other common CFS symptoms (e.g., chronic pain, lower psychomotor speed, and reduced physical activity).

METHODS

We used magnetic resonance imaging to quantify gray matter volume (GMV) and the N-acetylaspartate and N-acetylaspartylglutamate/creatine ratio (NAA/Cr) in a group of 89 women with CFS. Building on previous reports, we tested whether GMV and NAA/Cr in the dorsolateral prefrontal cortex are associated with fatigue severity, pain, psychomotor speed, and physical activity, while controlling for depressive symptoms. We also considered GMV and NAA/Cr differences between patients with CFS and 26 sex-, age-, and education-matched healthy controls.

RESULTS

The presence of pain symptoms was the main predictor of both GMV and NAA/Cr in the left dorsolateral prefrontal cortex of patients with CFS. More pain was associated with reduced GMVs and NAA/Cr, over and above the effects of fatigue, depressive symptoms, physical activity, and psychomotor speed. In contrast to previous reports and despite a large representative sample, global GMV did not differ between the CFS and healthy control groups.

CONCLUSIONS

CFS, as diagnosed by Centers for Disease Control and Prevention criteria, is not a clinical entity reliably associated with reduced GMV. Individual variation in the presence of pain, rather than fatigue, is associated with neuronal alterations in the dorsolateral prefrontal cortex of patients with CFS.

Potential drug therapies for the treatment of fibromyalgia

INTRODUCTION

Fibromyalgia (FM) is a common, complex chronic widespread pain condition is characterized by fatigue, sleep disturbance and cognitive dysfunction. Treatment of FM is difficult, requiring both pharmacological and non-pharmacological approaches, with an empiric approach to drug therapy focused toward individual symptoms, particularly pain. The effectiveness of current medications is limited with many patients discontinuing use.

AREAS COVERED

A systemic database search has identified 26 molecular entities as potential emerging drug therapies. Advances in the understanding of the pathophysiology of FM provides clues to targets for new medications. Investigation of bioamine modulation and α2δ ligands and novel targets such as dopamine receptors, NMDA receptors, cannabinoid receptors, melatonin receptors and potassium channels has identified potential drug therapies.

EXPERT OPINION

Modest improvement of health status in patients with FM has been observed with drugs targeting a diverse range of molecular mechanisms. No single drug, however, offered substantial efficacy against all the symptoms characteristic of FM. Identification of new and improved therapies for FM needs to address the heterogeneity of the condition, which suggests existence of patient subgroups, the relationship of central and peripheral aspects of the pathophysiology and a requirement of combination therapy with drugs targeting multiple molecular mechanisms.

Memantine elicits spinal blockades of motor function, proprioception, and nociception in rats

Although memantine blocks sodium currents and produces local skin anesthesia, spinal anesthesia with memantine is unknown. The purpose of the study was to evaluate the local anesthetic effect of memantine in spinal anesthesia and its comparison with a widely used local anesthetic lidocaine. After intrathecally injecting the rats with five doses of each drug, the dose-response curves of memantine and lidocaine were constructed. The potencies of the drugs and durations of spinal anesthetic effects on motor function, proprioception, and nociception were compared with those of lidocaine. We showed that memantine produced dose-dependent spinal blockades in motor function, proprioception, and nociception. On a 50% effective dose (ED50 ) basis, the rank of potency was lidocaine greater than memantine (P < 0.05 for the differences). At the equipotent doses (ED25 , ED50 , ED75 ), the block duration produced by memantine was longer than that produced by lidocaine (P < 0.05 for the differences). Memantine, but not lidocaine, displayed more sensory/nociceptive block than motor block. The preclinical data demonstrated that memantine is less potent than lidocaine, whereas memantine produces longer duration of spinal anesthesia than lidocaine. Memantine shows a more sensory-selective action over motor blockade.