Peripheral GABAA receptor activation modulates rat tongue afferent mechanical sensitivity

Burning mouth syndrome: a review of therapeutic approach

Burning mouth syndrome (BMS) is described by an intense burning sensation of the tongue or other oral areas without a clear etiopathology. The diagnosis of BMS is challenging due to variations of manifestations. The management of BMS is complicated due to the complex etiology of the disease. Many medications and treatment methods have been recommended for BMS management, but no one confirmed as the standard method. In this study, the therapeutic approaches of BMS were evaluated. The data of the article was obtained from PubMed/MEDLINE, Cochrane Library, and Web of Science. The following terms including "burning mouth syndrome", "therapy", and "treatment" were used for search in the databases. A wide range of articles about the therapeutic approach of BMS was searched and reviewed. Pharmacological and non-pharmacological approaches have been used for BMS management. Pharmacological treatments are including Capsaicin, Clonazepam, Low-dose aripiprazole, Alpha-lipoic acid, Duloxetine, Amitriptyline, Gabapentin, and Pregabalin, and ultra-micronized palmitoylethanolamide. Non-pharmacological therapies for BMS are cognitive therapy, Electroconvulsive therapy, Laser therapy, Acupuncture and auriculotherapy, Transcranial Magnetic Stimulation (rTMS), Salivary Mechanical Stimulation, and Botulinum Toxin. A detailed assessment of the etiology and pathophysiology of BMS, and having information about novel therapeutic interventions are essential for the management of BMS.

Use of a combination of N-acetylcysteine and clonazepam to treat burning mouth syndrome

OBJECTIVE

This study was intended to evaluate the clinical efficacy of a combination of N-acetylcysteine (NAC) and clonazepam for treatment of burning mouth syndrome (BMS).

STUDY DESIGN

A total of 160 patients with BMS were divided into 3 groups: group 1 received NAC (400 mg/d), group 2 received clonazepam (0.5 mg/d), and group 3 received both NAC and clonazepam. We evaluated symptom relief after 8 weeks of treatment using a visual analog scale (VAS). To assess oral health-related quality of life, we used the validated Korean version of an oral health impact profile (OHIP-14K).

RESULTS

The overall response rates of the 3 groups were 60.3%, 51.3%, and 80.0%, respectively. The mean VAS and OHIP-14K scores significantly decreased in all groups after the 8-week treatments. The VAS score changes were -12.2 ± 19.5, -10.0 ± 14.1, and -21.0 ± 24.6, respectively (P = .001), in the 3 groups and the OHIP-14K changes were -2.3 ± 9.2, -4.4 ± 6.9, and -8.7 ± 10.3, respectively (P = .020). Group 3 showed significantly larger differences in VAS and OHIP-14K scores than group 2, before and after treatment.

CONCLUSIONS

In the treatment of BMS, the NAC/clonazepam combination therapy was more effective than either monotherapy.

Attenuation of Sensory Transmission Through the Rat Trigeminal Ganglion by GABA Receptor Activation

While the trigeminal ganglion is often considered a passive conduit of sensory transmission, neurons and satellite glial cells (SGCs) within it can release neurotransmitters and express neuroreceptors. Some trigeminal ganglion neurons contain the neurotransmitter γ-aminobutyric acid (GABA) and express GABA receptors. There is behavioral evidence that increased GABA levels in the trigeminal ganglion decreases nociception, while a loss of GABA receptors results in hyperalgesia, although the neural mechanisms for this remain to be investigated. In this study, the expression of GABA receptors by trigeminal ganglion neurons that innervate rat labial skin and masseter muscle was compared using immunohistochemistry. The effect of intraganglionic administration of GABA receptor agonists was investigated by single unit recording of trigeminal brainstem and ganglion neuron responses to stimulation of the labial skin and/or masseter muscle in anesthetized rats. The mean frequency of expression of GABA_A and GABA_B receptors by masseter and labial skin ganglion neurons was 62.5% and 92.7%, and 55.4% and 20.3%, respectively. The expression of both GABA receptors was significantly greater in skin ganglion neurons. Masticatory muscle evoked brainstem trigeminal neuron responses were significantly attenuated by intraganglionic injection of muscimol (GABA_A) but not baclofen (GABA_B). The mechanical sensitivity of slow and fast conducting masticatory muscle afferent fibers was decreased and increased, respectively, by intraganglionic injection of both muscimol and baclofen. Activation of GABA_A receptors may exert a gating effect on sensory transmission through the trigeminal ganglion by decreasing putative nociceptive input and enhancing innocuous sensory input.

Burning mouth syndrome: An update

Background:

Burning mouth syndrome (BMS) is a chronic and debilitating oral pain of the normal oral mucosa. It mainly affects women in their fifth to seventh decade. Its aetiopathogenesis remains unclear and is probably of multifactorial origin, with increasing evidence that BMS may be a neuropathic disorder. BMS is classified as an idiopathic (nociplastic) orofacial pain with or without somatosensory changes by International Classification of Orofacial Pain (ICOP 2020). The diagnosis of BMS, having excluded ‘oral burning mouth symptoms’, has evolved from basic intraoral exclusion screening to extensive clinical and laboratory investigations, which include the screening of comorbidities and other chronic pains and somatosensory testing. There is no standardised treatment in managing BMS, but a proposed combination of supportive and pharmacological treatment has been recommended.

Aim:

To review the current concepts of BMS definitions, classifications, aetiopathogenesis, diagnosis techniques, and evidence-based treatments in managing BMS patients.

Conclusion:

As BMS is a diagnosis by exclusion, thus a stratified approach is required for assessment of patients presenting BMS. A BMS diagnosis protocol is desired using a standardised screening to distinguish BMS from patient’s presenting with ‘oral burning symptoms’, and evaluation of comorbid chronic pain disorders or other medical comorbidities, which will include haematological, fungal, salivary flow, and qualitative sensory testing. Axis II and other additional quantitative sensory testing may further elucidate the causes of this condition. For future BMS prediction and prevention, will be based upon research on the relationship between other chronic pain disorders and familial history, environmental and genetic information.

A perspective from experimental studies of burning mouth syndrome

Burning mouth syndrome (BMS) is one of the most frequently seen idiopathic pain conditions in a dental setting. Peri- and postmenopausal women are most frequently affected, and patients who experience BMS complain of persistent burning pain mainly at the tip and the bilateral border of the tongue. Recent studies have assessed whether BMS is a neuropathic pain condition, based on morphologic changes in biopsied tongue specimens, and whether there are abnormal pain responses in patients with this disease. Somatosensory studies have reported some abnormal findings in sensory and pain detection thresholds with inconsistency; however, the most distinct finding was exaggerated responses to painful stimuli. Imaging and electrophysiologic studies have suggested the possibility of dysregulation of the pain-modulating system in the central nervous system, which may explain the enhanced pain responses despite the lack of typical responses toward quantitative sensory tests. Basic studies have suggested the possible involvement of neuroprotective steroids, although the underlying mechanisms of this condition have not been elucidated. Experimental studies are looking for preferable supportive therapies for BMS patients despite the obscure pathogenesis.

The pro-algesic effect of γ-aminobutyric acid (GABA) injection into the masseter muscle of healthy men and women

Background and aims

Preclinical studies have reported that activation of peripheral γ-aminobutyric acid A (GABAA) receptors may result in analgesia. The current study was conducted in young healthy men (n = 30) and women (n = 28) to determine whether injections of GABA into the masseter muscle reduce pain in a sex-related manner.

Methods

The effect of injection of GABA alone, or in combination with the non-inflammatory algogen glutamate, was assessed in two separate studies. Lorazepam, a positive allosteric modulator of the GABAA-receptor, was co-injected with GABA in both studies to explore the role of this receptor in muscle pain responses of healthy human volunteers. Masticatory muscle mechanical pain intensity was recorded on an electronic visual analogue scale (VAS) while muscle pain sensitivity was assessed by determining the pressure pain threshold (PPT), tolerance and maximal jaw opening (MJO) of the subjects prior to, and again after the various intramuscular injections.

Results

Intramuscular injection of GABA alone was reported to be significantly more painful, in a concentration related manner, than saline control injections, and this pain was further increased by co-injection of lorazepam with GABA. Co-injection of GABA with glutamate was found to significantly increase glutamate-evoked masseter muscle pain in men, but not in women. There was no effect of injections of either GABA alone, or GABA with glutamate, on PPT, tolerance or maximum jaw opening.

Conclusions

Injection of GABA into the human masseter muscle appears to excite nociceptors to produce muscle pain without a longer term effect on mechanical pain sensitivity in the muscle. The findings suggest that GABA-mediated pain in humans is produced through peripheral GABAA receptor activation. The mechanism underlying the sex-related difference in the effect of GABA on glutamate-evoked muscle pain was speculated to be due to a methodological artifact.

Implications

This study was designed to detect analgesic rather than algesic effects of peripherally administered GABA, and as a result, the concentration of glutamate chosen for injection was close to the maximal pain response for healthy women, based on previously determined pain-concentration response relationships for glutamate. This may explain the finding of greater pain in men than women, when GABA and glutamate were co-injected. Overall, the findings suggest that activation of peripheral GABAA receptors in human masticatory muscle produces pain, possibly due to depolarization of the masticatory muscle afferent fibers.

Peripheral GABA receptors regulate colonic afferent excitability and visceral nociception

KEY POINTS

While the presence of GABA receptors on primary afferents has been well described, most functional analyses have focused on the regulation of transmitter release from central terminals and/or signalling in the sensory neuron cell body. Evidence that GABA receptors are transported to peripheral terminals and that there are several sources of GABA in the colon raise the possibility that GABA signalling in the periphery may influence colonic afferent excitability. GABA_A and GABA_B are present and functional in the colon, where exogenous agonists decrease the excitability of colonic afferents and suppress visceral nociception. Endogenous GABA release within the colon is sufficient to establish the resting excitability of colonic afferents as well as the behavioural response to noxious stimulation of the colon, primarily via GABA_A receptors. Peripheral GABA receptors may serve as a viable target for the treatment of visceral pain.

ABSTRACT

It is well established that GABA receptors at the central terminals of primary afferent fibres regulate afferent input to the superficial dorsal horn. However, the extent to which peripheral GABA signalling may also regulate afferent input remains to be determined. The colon was used to explore this issue because of the numerous endogenous sources of GABA that have been described in this tissue. The influence of GABA signalling on colonic afferent excitability was assessed in an ex vivo mouse colorectum pelvic nerve preparation where test compounds were applied to the receptive field. The visceromotor response (VMR) evoked by noxious colorectal distension was used to assess the impact of GABA signalling on visceral nociception, where test compounds were applied directly to the colon. Application of either GABA_A or GABA_B receptor agonists attenuated the colonic afferent response to colon stretch. Conversely, GABA_A and GABA_B receptor antagonists increased the stretch response. However, while the noxious distension-induced VMR was attenuated in the presence of GABA_A and GABA_B receptor agonists, the VMR was only consistently increased by GABA_A receptor antagonists. These results suggest that GABA receptors are present and functional in the peripheral terminals of colonic afferents and activation of these receptors via endogenous GABA release contributes to the establishment of colonic afferent excitability and visceral nociception. These results suggest that increasing peripheral GABA receptor signalling could be used to treat visceral pain.

Is there an association between drugs and burning mouth syndrome? A case-control study

OBJECTIVE

The purpose of this case-control study was to compare the pharmacological anamnesis collected from a group of 150 burning mouth syndrome (BMS) patients with that of a control group of 150 patients matched for age and sex.

MATERIALS AND METHODS

The patients' medical histories were reviewed, and data on drug therapy were collected. Drugs were classified on the basis of pharmacological effects; the classes were antihypertensives (i.e., ACE inhibitors/ARBs, calcium antagonists, diuretics and beta-blockers), antiaggregants, anticoagulants, antidiabetics, vitamin D integrators, bisphosphonates, psychotropics (i.e., anxiolytics and antidepressants), gastroprotectors, statins, thyroid hormone substitutes, corticosteroids and immunosuppressants.

RESULTS

The BMS patients and the controls were matched for age (mean age: 69 years) and sex (128 females and 22 males). Antihypertensives, especially ACE inhibitors/ARBs (OR = 0.37, CI: 0.22-0.63, p = 0.0002) and beta-blockers (OR = 0.36, CI: 0.19-0.68 p = 002), revealed an inverse association with the presence of BMS, whereas anxiolytics (OR = 3.78, CI: 2.12-6.75 p < 0.0001), but neither antidepressants nor antipsychotics, were significantly associated with BMS. There were no correlations with other drug classes.

CONCLUSION

Our study highlighted that ACE inhibitors, ARBs and beta-blockers were in inverse relation to BMS and found that anxiolytics, but neither antidepressants nor antipsychotics, were linked to the presence of the syndrome.

Psycho-stomatodynia

Introduction:Burning mouth syndrome is an enigmatic condition whose etiopathogenic origin remains largely unknown and whose treatment remains unsatisfactory. It is often considered to be of “psychosomatic” origin, and this etiology is frequently reported in the French medical literature.Corpus:This narrative review examines the arguments supporting this point of view, in its historical, clinical, and therapeutic aspects, in order to shed light on the patientʼs point of view.Conclusion:The etiopathogenic uncertainty does not let us give the patient an erroneous conception of the affliction.

Refractory burning mouth syndrome: clinical and paraclinical evaluation, comorbiities, treatment and outcome

BACKGROUND

Burning Mouth Syndrome (BMS) is a chronic pain condition characterized by persistent intraoral burning without related objective findings and unknown etiology that affects elderly females mostly. There is no satisfactory treatment for BMS. We aimed to observe the long-term efficacy of high velanfaxine doses combined with systemic and topical administered clonazepam in a particular subgroup of BMS patients who do not respond to current clinical management.

RESULTS

Eight (66.1 ± 6.2 years old females) out of 14 BMS patients fulfilled the inclusion criteria and were treated with venlafaxine (300 mg/d) and clonazepam (5 mg/d) for 35.4 ± 12.1 (mean ± SD) months. The average duration of the symptoms at baseline was 4.3 ± 1.4 years and the overall mean daily pain intensity score was 8.6 ± 1.3 (VAS); pain was in tongue and within the oral mucosa, accompanying by oral and facial dysesthesia. In five patients tasting was abnormal. All patients had positive history of concomitant primary headache. The average score of Hamilton Rating scale for Anxiety and Depression was 21 ± 4.2, and 26.1 ± 2.9, respectively. Previous ineffective treatments include anticonvulsants and anti-depressants. All patients responded (more than 50% decrease in VAS) after three months treatment (mean VAS 3.2 ± 2.2) with no remarkable adverse events.

CONCLUSION

BMS deserves bottomless psychiatric evaluation and management when current available treatments fail. Treatment with venlafaxine combined with topical and systemic clonazepam may be effective in refractory BMS cases but further investigation in a large-scale controlled study is needed to confirm these results.

Burning Mouth Syndrome: Aetiopathogenesis and Principles of Management

Burning mouth syndrome (BMS) is a chronic debilitating oral condition characterised by a burning sensation of the oral mucosa in an otherwise apparently normal person. Its aetiology and pathogenesis are obscure, but both psychogenic factors and peripheral and central neuropathies appear to be implicated. There is no cure for BMS, and treatment with either local or systemic medications focuses on the relief of symptoms and on improving quality of life. In recalcitrant cases, psychological/psychiatric intervention may be helpful. In order to improve treatment outcomes, a better understanding of the pathogenesis of this syndrome might provide a basis for the development of more effective management strategies. In this short review, we discuss current knowledge of the diagnosis, aetiopathogenesis, and management of BMS.

Burning mouth syndrome

Objective

To review the clinical entity of primary burning mouth syndrome (BMS), its pathophysiological mechanisms, accurate new diagnostic methods and evidence-based treatment options, and to describe novel lines for future research regarding aetiology, pathophysiology, and new therapeutic strategies.

Description

Primary BMS is a chronic neuropathic intraoral pain condition that despite typical symptoms lacks clear clinical signs of neuropathic involvement. With advanced diagnostic methods, such as quantitative sensory testing of small somatosensory and taste afferents, neurophysiological recordings of the trigeminal system, and peripheral nerve blocks, most BMS patients can be classified into the peripheral or central type of neuropathic pain. These two types differ regarding pathophysiological mechanisms, efficacy of available treatments, and psychiatric comorbidity. The two types may overlap in individual patients. BMS is most frequent in postmenopausal women, with general population prevalence of around 1%. Treatment of BMS is difficult; best evidence exists for efficacy of topical and systemic clonazepam. Hormonal substitution, dopaminergic medications, and therapeutic non-invasive neuromodulation may provide efficient mechanism-based treatments for BMS in the future.

Conclusion

We present a novel comprehensive hypothesis of primary BMS, gathering the hormonal, neuropathic, and genetic factors presumably required in the genesis of the condition. This will aid in future research on pathophysiology and risk factors of BMS, and boost treatment trials taking into account individual mechanism profiles and subgroup-clusters.