Burning mouth syndrome as a trigeminal small fibre neuropathy: Increased heat and capsaicin receptor TRPV1 in nerve fibres correlates with pain score

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.

Characterization of burning mouth syndrome profiles based on response to a local anaesthetic lozenge

OBJECTIVE

Burning mouth syndrome (BMS) is a chronic oral pain condition with unknown aetiology but assumed to involve peripheral/central neuropathological and immune-mediated inflammatory factors. We aimed at characterizing inflammatory and neurogenic profiles and oral symptomatology of patients with BMS based on response to a local anaesthetic lozenge.

METHODS

Patients with BMS were divided into an Effect (n = 13), No effect (n = 8) or Unspecified (n = 2) group according to their response to a local anaesthetic lozenge on oral pain. Inflammation was assessed in blood plasma and saliva by analyses of IL-6, IL-8, IL-17A, IL-23 and TNF-α levels. The degree of inflammation and distribution of oestrogen receptor, NGF, NGF-receptor, TRPV-1 and IL-17F in buccal mucosal tissue were investigated by immunohistochemistry.

RESULTS

Immunoreactivity to the oestrogen receptor was most intense in the Effect group, whereas the No effect group tended to have higher plasma levels of the pro-inflammatory cytokines.

CONCLUSIONS

Our findings indicate that the response to treatment with local anaesthesia enables subgrouping of patients with BMS according to the potential pathogenic mechanisms. Effect of local anaesthesia indicates a peripheral neuropathology involving lack of oestrogen and upregulation of oestrogen receptors, and no effect indicates a systemic inflammation-induced mechanism leading to increased levels of plasma cytokines.

Anatomical stability of human fungiform papillae and relationship with oral perception measured by salivary response and intensity rating

Fungiform papillae house taste buds on the anterior dorsal tongue. Literature is inconclusive as to whether taste perception correlates with fungiform papillae density (FPD). Gustatory reflexes modulate the amount and composition of saliva subsequently produced, and thus may be a more physiologically objective measure of tastant-receptor interactions. Taste perception fluctuates with time but the stability of individual fungiform papillae is unclear. This study followed ten healthy volunteers longitudinally at baseline, one and six months. FPD, diameter and position were measured and participants rated intensity perception of sucrose, caffeine, menthol and capsaicin solutions. Salivary flow rate, protein concentration and relative changes in protein composition were measured following each tastant. FPD, diameter and position were unchanged at six months. FPD did not correlate with intensity rating for any taste. FPD did correlate with changes in salivary protein output following sucrose (ρ = 0.72, p = 0.02) and changes in levels of proline-rich protein and mucin 7 following capsaicin (ρ = 0.71, p = 0.02, ρ = 0.68, p = 0.04, respectively). These results suggest that over six months fungiform papillae are anatomically stable, playing a greater role in mediating the physiological salivary response to stimuli rather than determining the perceived intensity of taste.

Effect of antidepressant treatment on plasma levels of neuroinflammation-associated molecules in patients with somatic symptom disorder with predominant pain around the orofacial region

OBJECTIVE

Burning mouth syndrome (BMS) and atypical odontalgia (AO) are examples of somatic symptom disorders with predominant pain around the orofacial region. Neuroinflammation is thought to play a role in the mechanisms, but few studies have been conducted. We aimed to better understand the role of neuroinflammation in the pathophysiology and treatment of BMS/AO.

METHODS

Plasma levels of 28 neuroinflammation-related molecules were determined in 44 controls and 48 BMS/AO patients both pretreatment and 12-week post-treatment with duloxetine.

RESULTS

Baseline plasma levels of interleukin (IL)-1β (p < .0001), IL-1 receptor antagonist (p < .001), IL-6 (p < .0001), macrophage inflammatory protein-1β (p < .0001), and platelet-derived growth factor-bb (.04) were significantly higher in patients than in controls. Plasma levels of granulocyte macrophage colony stimulating factor were significantly higher in patients than in controls (p < .001) and decreased with treatment (.009). Plasma levels of eotaxin, monocyte chemoattractant protein-1, and vascular endothelial growth factor decreased significantly with treatment (p < .001, .022, and .029, respectively).

CONCLUSIONS

Inflammatory mechanisms may be involved in the pathophysiology and/or treatment response of somatic symptom disorders with predominant pain around the orofacial region.

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.

Capsaicin: Physicochemical properties, cutaneous reactions and potential applications in painful and inflammatory conditions

Capsaicin is a natural protoalkaloid recognized as the main pungent component in hot peppers (Capsicum annuum L.). The capsaicin receptor is highly expressed in the unmyelinated type C nerve fibers originating from small diameter sensory neurons in dorsal root ganglia and cranial nerve ganglia correspondents. Capsaicin and related vanilloids have a variety of effects on primary sensory neurons function, from sensory neuron excitation characterized by local burning sensation and neurogenic inflammation, followed by conduction blockage accompanied by reversible ultrastructural changes of peripheral nociceptive endings (desensitization), going as far as irreversible degenerative changes (neurotoxicity). The main role in capsaicin-induced neurogenic inflammation relies on the capsaicin sensitive, small diameter primary sensory neurons, therefore its evaluation could be used as a diagnostic instrument in functional alterations of cutaneous sensory nerve fibers. Moreover, capsaicin-induced desensitization and neurotoxicity explain the analgesic/anti-nociceptive and anti-inflammatory effects of topical capsaicin and its potential use in the management of painful and inflammatory conditions. In this study, we describe the effects of capsaicin on neurogenic inflammation and nociception, as well as its potential diagnostic value and therapeutic impact in various conditions involving impairment of sensory nerve fibers.

An updated review on pathophysiology and management of burning mouth syndrome with endocrinological, psychological and neuropathic perspectives

Burning mouth syndrome (BMS) is a chronic oro-facial pain disorder of unknown cause. It is more common in peri- and post-menopausal women, and sex hormone dysregulation is believed to be an important causative factor. Psychosocial events often trigger or exacerbate symptoms, and persons with BMS appear to be predisposed towards anxiety and depression. Atrophy of small nerve fibres in the tongue epithelium has been reported, and potential neuropathic mechanisms for BMS are now widely investigated. Historically, BMS was thought to comprise endocrinological, psychosocial and neuropathic components. Neuroprotective steroids and glial cell line-derived neurotrophic factor family ligands may have pivotal roles in the peripheral mechanisms associated with atrophy of small nerve fibres. Denervation of chorda tympani nerve fibres that innervate fungiform buds leads to alternative trigeminal innervation, which results in dysgeusia and burning pain when eating hot foods. With regard to the central mechanism of BMS, depletion of neuroprotective steroids alters the brain network-related mood and pain modulation. Peripheral mechanistic studies support the use of topical clonazepam and capsaicin for the management of BMS, and some evidence supports the use of cognitive behavioural therapy. Hormone replacement therapy may address the causes of BMS, although adverse effects prevent its use as a first-line treatment. Selective serotonin reuptake inhibitors (SSRIs) and serotonin and noradrenaline reuptake inhibitors (SNRIs) may have important benefits, and well-designed controlled studies are expected. Other treatment options to be investigated include brain stimulation and TSPO (translocator protein 18 kDa) ligands.

Is burning mouth syndrome a neuropathic pain condition?

Primary burning mouth syndrome (BMS) is defined as an "intraoral burning or dysaesthetic sensation, recurring daily… more than 3 months, without clinically evident causative lesions" (IHS 2013). In addition to pain, taste alterations are frequent (dysgeusia, xerostomia). Although lacking clinical signs of neuropathy, more accurate diagnostic methods have shown neuropathic involvement at various levels of the neuraxis in BMS: peripheral small fiber damage (thermal quantitative sensory testing, electrogustatometry, epithelial nerve fiber density), trigeminal system lesions in the periphery or the brainstem (brainstem reflex recordings, trigeminal neurography, evoked potentials), or signs of decreased inhibition within the central nervous system (deficient brainstem reflex habituation, positive signs in quantitative sensory testing, neurotransmitter-positron emission tomography findings indicative of deficient striatal dopamine function). Abnormalities in electrogustatometry indicate the involvement of the small Aδ taste afferents, in addition to somatosensory small fibers. According to these findings, the clinical entity of BMS can be divided into 2 main subtypes compatible with either peripheral or central neuropathic pain, which may overlap in individual patients. The central type does not respond to local treatments and associates often with psychiatric comorbidity (depression or anxiety), whereas the peripheral type responds to peripheral lidocaine blocks and topical clonazepam. Burning mouth syndrome is most prevalent in postmenopausal women, having led to a hypothesis that BMS is triggered as a consequence of nervous system damage caused by neurotoxic factors affecting especially vulnerable small fibers and basal ganglia in a setting of decrease in neuroprotective gonadal hormones and increase in stress hormone levels, typical for menopause.

Proteomic profiling of whole-saliva reveals correlation between Burning Mouth Syndrome and the neurotrophin signaling pathway

Burning mouth syndrome (BMS) is characterized by a spontaneous and chronic sensation of burning in the oral mucosa, with no apparent signs. The underlying pathophysiological and neuropathic mechanisms remain unclear. Here, we attempt to elucidate some of these mechanisms using proteomic profiling and bioinformatic analyses of whole-saliva (WS) from BMS patients compared to WS from healthy individuals. Qualitative and quantitative proteomic profiling was performed using two dimensional gel electrophoresis (2-DE) and quantitative mass spectrometry (q-MS). In order to improve protein visibility, 21 high abundance proteins were depleted before proteomic profiling. Quantitative proteomic analysis revealed 100 BMS specific proteins and an additional 158 proteins up-regulated by more than threefold in those with BMS. Bioinformatic analyses of the altered protein expression profile of BMS group indicated high correlations to three cellular mechanisms including the neurotrophin signaling pathway. Based on this finding, we suggest that neurotrophin signaling pathway is involved in the pathophysiology of BMS by amplifying P75NTR activity, which in turn increases neural apoptosis thereby reducing sub-papillary nerve fiber density in the oral mucosa.

Neurophysiology and genetics of burning mouth syndrome

BACKGROUND AND AIMS

Neuropathic mechanisms are involved in burning mouth syndrome (BMS), and variation of the dopamine D2 receptor (DRD2) gene contributes to experimental pain perception. We investigated whether neurophysiologic findings differ in BMS patients compared to healthy controls, and whether 957C>T polymorphism of the DRD2 gene influences thermal sensitivity or pain experience in BMS.

METHODS

Forty-five BMS patients (43 women), mean age 62.5 years, and 32 healthy controls (30 women), mean age 64.8 years, participated. Patients estimated pain intensity, interference, suffering and sleep with Numeric Rating Scale. Blink reflex tests of the supraorbital (SON), mental (MN) and lingual (LN) nerves, and thermal quantitative sensory testing were done. The results were analysed with ANOVA. DRD2 gene 957C>T polymorphism was determined in 31 patients, and its effects on neurophysiologic and clinical variables were analysed.

RESULTS

Cool (p = 0.0090) and warm detection thresholds (p = 0.0229) of the tongue were higher in BMS patients than controls. The stimulation threshold for SON BR was higher in patients than in controls (p = 0.0056). The latencies of R2 component were longer in BMS patients than in controls (p = 0.0005) at the SON distribution. Habituation of SON BR did not differ between the groups. The heat pain thresholds were highest (p = 0.0312) in homozygous patients with 957TT, who also reported most interference (p = 0.0352) and greatest suffering (p = 0.0341). Genotype 957CC associated with sleep disturbances (p = 0.0254).

CONCLUSIONS

Burning mouth syndrome patients showed thermal hypoesthesia within LN distribution compatible with small fibre neuropathy. The DRD2 957C>T genotype influences perception and experience of BMS pain.

SIGNIFICANCE

The results confirm earlier findings of neuropathic pain in BMS. The DRD2 957 C>T genotype influences perception and experience of clinical pain in BMS.

Oral burning: local and systemic connection for a patient-centric approach

Burning symptoms in the oral cavity are caused by a range of systemic and local factors, in addition to the neuropathic pain disorder burning mouth syndrome (BMS). Patients may state oral burning as a standalone symptom or may report as a secondary symptom in association with other factors, most commonly with oral dryness, oral mucosal lesions, or certain systemic conditions. There is a level of uncertainty in the presentation of this condition which creates a diagnostic challenge from both the patient's perspective and the practitioner evaluating these individuals. The diagnoses are complicated due to the lack of a clear definition of BMS and clinical guidelines to distinguish BMS from other conditions that are responsible for oral burning symptoms. A clinician should be able to differentiate oral burning from burning mouth syndrome. This integrative review discusses on local and systemic etiologies of oral burning based on current evidence that needs to be excluded for a diagnosis of BMS. It also provides an algorithm for diagnostic workup and therapeutic management to medical providers for patients experiencing oral burning symptoms. This comprehensive system provides a systematic stepwise workup in diagnosing and managing patients presenting with a complaint of oral burning that optimally meets a predictive, preventive, and personalized medicine (PPPM) approach.

The orotrigeminal system

The trigeminal sensory nerve fiber branches supply afferent information from the skin and mucous membranes of the face and head and the oral cavity regarding information on temperature, touch, and pain. Under normal conditions, the trigeminal nerve serves to provide important information from nerve fibers and tissues using specialized receptors sensitive for irritant and painful stimuli. The current scientific consensus indicates that nerve endings responsible for chemical and thermal sensitivity of the skin and mucous membranes are the same nerves responsible for nociception. This "chemesthetic sense" allows many vertebrates to detect chemical agonists that induce sensations such as touch, burning, stinging, tingling, or changes in temperature. Research has been under way for many years to determine how exposure of the oral and/or nasal cavity to compounds that elicit pungent or irritant sensations can produce these sensations. In addition, these chemicals can alter other sensory information such as taste and smell to affect the flavor of foods and beverages. We now know that these 'chemesthetic molecules' are agonists of molecular receptors, which exist on primary afferent nerve fibers that innervate the orofacial area. However, under pathophysiologic conditions, over- or underexpression or activity of these receptors may lead to painful orotrigeminal syndromes. Some of these individual receptors are discussed in detail, including transient receptor potential channels and acid sensing ion channels, among others.

Focal localization of inflammatory cytokines and neurotrophins in a tongue chronic injury model

OBJECTIVES

Chronic injury in tongue causes the variety of reactions in the oral cavity, frequently leading to its functional and structural disintegrity including inflammation and sensory dysfunction, but its detailed profiles were not elucidated yet. One of the chronically injured tongue such as tongue piercing, as a pathological aspect, is currently popular among younger people but may be associated with severe side effects, leading to pathophysiological complications. However, the pathophysiological aspects and related cellular and molecular mechanisms underlying tongue injury are not clearly understood.

DESIGN

In this study, we designed an experimental model system using C57BL/6 male mice that mimics a chronically injured situation by penetrating the middle part of tongue with silk suture. After 5 and 10 days mice were sacrificed and tongues were collected and processed for histological evaluation and immunohistochemistry.

RESULTS

We found that the anterior tongue showed localization of neuro-inflammatory signaling molecules such as myeloperoxidase (MPO), matrix metalloproteinase 2 (MMP2), tumor necrosis factor-α (TNF-α), nerve growth factor, and transient receptor potential cation channel subfamily V member 1 (TRPV1) without any apparent inflammation in temporal manner. In addition, the signal for AM1-43, an activity-dependent nerve terminal probe, decreased within the fungiform papillae on the anterior tongue after injury.

CONCLUSIONS

These results implied that the distinct localizations of inflammatory cytokines and neurotrophin would contribute altered sensory function in anterior tongue following the chronic injury. Our study indicates the possible pathophysiologic mechanism underlying neuro-inflammation following chronically injury of tongue. In addition, it could be cautiously postulated that mechanical injury should be avoided to prevent chronic pain disorders from being triggered.

Impaired Junctions and Invaded Macrophages in Oral Epithelia With Oral Pain

Recurrent or chronic oral pain is a great burden for patients. Recently, the links between epithelial barrier loss and disease were extended to include initiation and propagation. To explore the effects of pathohistological changes in oral epithelia on pain, we utilized labial mucosa samples in diagnostic labial gland biopsies from patients with suspected Sjögren's syndrome (SS), because they frequently experience pain and discomfort. In most labial mucosa samples from patients diagnosed with SS, disseminated epithelial cellular edema was prevalent as ballooning degeneration. The disrupted epithelia contained larger numbers of infiltrating macrophages in patients with oral pain than in patients without pain. Immunohistochemistry revealed that edematous areas were distinct from normal areas, with disarranged cell-cell adhesion molecules (filamentous actin, E-cadherin, β-catenin). Furthermore, edematous areas were devoid of immunostaining for transient receptor potential channel vanilloid 4 (TRPV4), a key molecule in adherens junctions. In an investigation on whether impaired TRPV4 affect cell-cell adhesion, calcium stimulation induced intimate cell-cell contacts among oral epithelial cells from wild-type mice, while intercellular spaces were apparent in cells from TRPV4-knockout mice. The present findings highlight the relationship between macrophages and epithelia in oral pain processing, and identify TRPV4-mediated cell-cell contacts as a possible target for pain treatment.

TRPV1-Like Immunoreactivity in the Human Locus K, a Distinct Subregion of the Cuneate Nucleus

The presence of transient receptor potential vanilloid type-1 receptor (TRPV1)-like immunoreactivity (LI), in the form of nerve fibres and terminals, is shown in a set of discrete gray matter subregions placed in the territory of the human cuneate nucleus. We showed previously that those subregions share neurochemical and structural features with the protopathic nuclei and, after the ancient name of our town, collectively call them Locus Karalis, and briefly Locus K. TRPV1-LI in the Locus K is codistributed, though not perfectly overlapped, with that of the neuropeptides calcitonin gene-related peptide and substance P, the topography of the elements immunoreactive to the three markers, in relation to each other, reflecting that previously described in the caudal spinal trigeminal nucleus. Myelin stainings show that myelinated fibres, abundant in the cuneate, gracile and trigeminal magnocellular nuclei, are scarce in the Locus K as in the trigeminal substantia gelatinosa. Morphometric analysis shows that cell size and density of Locus K neurons are consistent with those of the trigeminal substantia gelatinosa and significantly different from those of the magnocellular trigeminal, solitary and dorsal column nuclei. We propose that Locus K is a special component of the human dorsal column nuclei. Its functional role remains to be determined, but TRPV1 appears to play a part in it.

Recent Advances in the Etiology and Treatment of Burning Mouth Syndrome

Burning mouth syndrome (BMS) is a debilitating condition that has a striking female predilection. Although the oral mucosa is normal in appearance, patients with BMS experience oral burning that most commonly localizes to the lips and tongue. BMS is a diagnosis of exclusion, and all underlying pathoses associated with allodynia must be ruled out prior to rendering the diagnosis. The etiopathogenesis of BMS remains poorly understood, and thus patient management is challenging. Data indicate that oral and systemic factors both contribute to the development and persistence of the condition. Of particular interest, emerging work identifies structural and functional deficits within the nervous system that may lead to a more mechanistic understanding of BMS pathology. In addition, several novel findings suggest that circadian rhythm dysfunction may be a previously unappreciated yet clinically significant driver of disease. Circadian rhythm controls pain perception, mood, and sleep and plays a key role in the regulation of the hypothalamic-pituitary-adrenal axis. Since these are altered in patients with BMS, this may be reflective of underlying circadian dysfunction. While evidence-based treatment strategies for BMS are lacking, current treatment approaches consist of local and systemic medications, such as clonazepam, alpha lipoic acid, capsaicin, low-level laser therapy, gabapentin, and amitriptylin. In addition, the use of cognitive behavioral therapy is reported. This review provides an overview of the recent literature related to the etiology and treatment of BMS and identifies current challenges facing researchers and clinicians alike.

Potential protein biomarkers for burning mouth syndrome discovered by quantitative proteomics

Burning mouth syndrome (BMS) is a chronic pain disorder characterized by severe burning sensation in normal looking oral mucosa. Diagnosis of BMS remains to be a challenge to oral healthcare professionals because the method for definite diagnosis is still uncertain. In this study, a quantitative saliva proteomic analysis was performed in order to identify target proteins in BMS patients’ saliva that may be used as biomarkers for simple, non-invasive detection of the disease. By using isobaric tags for relative and absolute quantitation labeling and liquid chromatography-tandem mass spectrometry to quantify 1130 saliva proteins between BMS patients and healthy control subjects, we found that 50 proteins were significantly changed in the BMS patients when compared to the healthy control subjects (p ≤ 0.05, 39 up-regulated and 11 down-regulated). Four candidates, alpha-enolase, interleukin-18 (IL-18), kallikrein-13 (KLK13), and cathepsin G, were selected for further validation. Based on enzyme-linked immunosorbent assay measurements, three potential biomarkers, alpha-enolase, IL-18, and KLK13, were successfully validated. The fold changes for alpha-enolase, IL-18, and KLK13 were determined as 3.6, 2.9, and 2.2 (burning mouth syndrome vs. control), and corresponding receiver operating characteristic values were determined as 0.78, 0.83, and 0.68, respectively. Our findings indicate that testing of the identified protein biomarkers in saliva might be a valuable clinical tool for BMS detection. Further validation studies of the identified biomarkers or additional candidate biomarkers are needed to achieve a multi-marker prediction model for improved detection of BMS with high sensitivity and specificity.

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.

Salivary changes in oral mucosal diseases

Saliva is a unique biological fluid that can be easily collected and analyzed with low cost and low morbidity. Therefore, there is a growing attention for using salivary biomarkers in the diagnosis and monitoring of disease progress and response to treatment. Salivary changes have been described in relation to oral mucosal diseases. This article discusses the causes and consequences of salivary hypofunction and presents a review of the literature related to changes in salivary parameters in various oral mucosal diseases and in systemic diseases with possible oral mucosal involvement.

Burning mouth syndrome: a systematic review of treatments

Burning mouth syndrome (BMS) is a chronic oral pain syndrome that primarily affects peri- and postmenopausal women. It is characterized by oral mucosal burning and may be associated with dysgeusia, paresthesia, dysesthesia, and xerostomia. The etiology of the disease process is unknown, but is thought to be neuropathic in origin. The goal of this systematic review was to assess the efficacy of the various treatments for BMS. Literature searches were conducted through PubMed, Web of Science, and Cochrane Library databases, which identified 22 randomized controlled trials. Eight studies examined alpha-lipoic acid (ALA), three clonazepam, three psychotherapy, and two capsaicin, which all showed modest evidence of potentially decreasing pain/burning. Gabapentin was seen in one study to work alone and synergistically with ALA. Other treatments included vitamins, benzydamine hydrochloride, bupivacaine, Catuama, olive oil, trazodone, urea, and Hypericum perforatum. Of these other treatments, Catuama and bupivacaine were the only ones with significant positive results in symptom improvement. ALA, topical clonazepam, gabapentin, and psychotherapy may provide modest relief of pain in BMS. Gabapentin may also boost the effect of ALA. Capsaicin is limited by its side effects. Catuama showed potential for benefit. Future studies with standardized methodology and outcomes containing more patients are needed.

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.

Analgesic effect of topical oral capsaicin gel in burning mouth syndrome

OBJECTIVE

To investigate the effectiveness of repeated topical application of oral capsaicin gel in two different concentrations for relief of burning/stinging sensations in patients with burning mouth syndrome (BMS).

MATERIAL AND METHODS

This randomized double-blind cross-over study included 22 female patients with BMS. The patients were randomized for topical application of either 0.01% or 0.025% oral capsaicin gel on the dorsal part of tongue three times daily for 14 days, followed by 14 days wash-out period, and finally treatment with the other concentration of oral gel three times daily for 14 days. A visual analogue scale (VAS) was used to assess the severity of pain five times during the intervention period.

RESULTS

18 patients completed the intervention. Their VAS score at baseline was 5.5 ± 0.6 cm (mean ± SD). Treatment with the two concentrations of capsaicin gels significantly improved the burning/stinging symptoms assessed on VAS compared with baseline (p = 0.002). There was no statistically significant difference between the two concentrations of the gels on relieving symptoms. Four patients dropped out during the intervention period due to gastrointestinal side-effects.

CONCLUSIONS

Topical capsaicin might be an alternative for the short-term treatment of BMS. However, further studies are needed to investigate especially the gastro-intestinal side-effects which may limit its long-term use.

Is it Sjögren's syndrome or burning mouth syndrome? Distinct pathoses with similar oral symptoms

Sjögren's syndrome (SS) and burning mouth syndrome (BMS) typically occur in postmenopausal women. Although these conditions have significantly different etiopathogeneses, patients with SS or BMS often present with analogous oral complaints. The similarities between the two conditions have led to considerable confusion on the part of medical and dental practitioners, and those with BMS or SS often wait years to receive a diagnosis. Therefore, it is imperative for clinicians to understand the characteristic subjective and objective features of each disease and how these can be used to distinguish them. This review will discuss the proposed etiology, clinical manifestations, histopathology, diagnostic criteria, and patient management of SS and BMS. We also identify key differences between the two pathoses that aid in establishing the correct diagnosis. Recognition of the defining features of each condition will lead to reduced time to diagnosis and improved patient management for these poorly understood conditions.

Interventions for treating burning mouth syndrome

BACKGROUND

Burning mouth syndrome (BMS) is a term used for oral mucosal pain (burning pain or discomfort in the tongue, lips or entire oral cavity) without identifiable cause. General population prevalence varies from 0.1% to 3.9%. Many BMS patients indicate anxiety, depression, personality disorders and impaired quality of life (QoL). This review updates the previous versions published in 2000 and 2005.

OBJECTIVES

To determine the effectiveness and safety of any intervention versus placebo for symptom relief and changes in QoL, taste, and feeling of dryness in people with BMS.

SEARCH METHODS

Cochrane Oral Health's Information Specialist searched the following databases: Cochrane Oral Health's Trials Register (to 31 December 2015), the Cochrane Central Register of Controlled Trials (CENTRAL; 2015, Issue 11) in the Cochrane Library (searched 31 December 2015), MEDLINE Ovid (1946 to 31 December 2015), and Embase Ovid (1980 to 31 December 2015). We searched ClinicalTrials.gov and the World Health Organization International Clinical Trials Registry Platform for ongoing trials. We placed no restrictions on the language or date of publication when searching the electronic databases SELECTION CRITERIA: Randomised controlled trials (RCTs) comparing any treatment against placebo in people with BMS. The primary outcomes were symptom relief (pain/burning) and change in QoL. Secondary outcomes included change in taste, feeling of dryness, and adverse effects.

DATA COLLECTION AND ANALYSIS

We used standard methodological procedures expected by Cochrane. Outcome data were analysed as short-term (up to three months) or long-term (three to six months).

MAIN RESULTS

We included 23 RCTs (1121 analysed participants; 83% female). Interventions were categorised as: antidepressants and antipsychotics, anticonvulsants, benzodiazepines, cholinergics, dietary supplements, electromagnetic radiation, physical barriers, psychological therapies, and topical treatments.Only one RCT was assessed at low risk of bias overall, four RCTs' risk of bias was unclear, and 18 studies were at high risk of bias. Overall quality of the evidence for effectiveness was very low for all interventions and all outcomes.Twenty-one RCTs assessed short-term symptom relief. There is very low-quality evidence of benefit from electromagnetic radiation (one RCT, 58 participants), topical benzodiazepines (two RCTs, 111 participants), physical barriers (one RCT, 50 participants), and anticonvulsants (one RCT, 100 participants). We found insufficient/contradictory evidence regarding the effectiveness of antidepressants, cholinergics, systemic benzodiazepines, dietary supplements or topical treatments. No RCT assessing psychological therapies evaluated short-term symptom relief.Four studies assessed long-term symptom relief. There is very low-quality evidence of a benefit from psychological therapies (one RCT, 30 participants), capsaicin oral rinse (topical treatment) (one RCT, 18 participants), and topical benzodiazepines (one RCT, 66 participants). We found no evidence of a difference for dietary supplements or lactoperoxidase oral rinse. No studies assessing antidepressants, anticonvulsants, cholinergics, electromagnetic radiation or physical barriers evaluated long-term symptom relief.Short-term change in QoL was assessed by seven studies (none long-term).The quality of evidence was very low. A benefit was found for electromagnetic radiation (one RCT, 58 participants), however findings were inconclusive for antidepressants, benzodiazepines, dietary supplements and physical barriers.Secondary outcomes (change in taste and feeling of dryness) were only assessed short-term, and the findings for both were also inconclusive.With regard to adverse effects, there is very low-quality evidence that antidepressants increase dizziness and drowsiness (one RCT, 37 participants), and that alpha lipoic acid increased headache (two RCTs, 118 participants) and gastrointestinal complaints (3 RCTs, 138 participants). We found insufficient/contradictory evidence regarding adverse events for anticonvulsants or benzodiazepines. Adverse events were poorly reported or unreported for cholinergics, electromagnetic radiation, and psychological therapies. No adverse events occurred from physical barriers or topical therapy use.

AUTHORS' CONCLUSIONS

Given BMS' potentially disabling nature, the need to identify effective modes of treatment for sufferers is vital. Due to the limited number of clinical trials at low risk of bias, there is insufficient evidence to support or refute the use of any interventions in managing BMS. Further clinical trials, with improved methodology and standardised outcome sets are required in order to establish which treatments are effective. Future studies are encouraged to assess the role of treatments used in other neuropathic pain conditions and psychological therapies in the treatment of BMS.

Estrogens Exacerbate Nociceptive Pain via Up-Regulation of TRPV1 and ANO1 in Trigeminal Primary Neurons of Female Rats

Several trigeminal pain disorders show sex differences, and high levels of estrogens may underlie these differences. The interaction between transient receptor potential vanilloid 1 (TRPV1) and anoctamin 1 (ANO1) plays an important role in peripheral nociception. However, whether TRPV1 and ANO1 are involved in estrogen-modulated trigeminal pain sensitivity is unclear. In this study, we examined estradiol (E2) modulation of nociception through behavioral and immunohistological experiments after application of capsaicin (Cap), a selective TRPV1 agonist, onto the ocular surface in ovariectomized rats treated with high-dose E2 (HE) or low-dose E2 (LE) for 2 days. In addition, we used real-time PCR to study the effects of E2 on the expression levels of TRPV1 and ANO1 mRNA in trigeminal ganglia. In the behavioral experiment, the HE group showed significant potentiation of Cap-evoked nocifensive behavior compared with the LE group. Immunohistochemistry showed that Cap evoked a significantly greater number of cells that were immunoreactive for c-Fos, a marker of nociceptive activation, in the trigeminal subnucleus caudalis/upper cervical cord in the HE group than in the LE group. The number of c-Fos-immunoreactive cells in the ventral trigeminal interpolaris/caudalis were similar in the 2 groups. Real-time PCR showed that the levels of TRPV1 and ANO1 mRNA in the HE group were significantly higher than levels in the LE group. Thus, high levels of estrogens may be a risk factor for Cap-evoked nociceptive pain, and estrogen-dependent increases in TRPV1 and ANO1 are likely involved in modulating the nociceptive response in the trigeminal area.

TRPV1 receptor in the human trigeminal ganglion and spinal nucleus: immunohistochemical localization and comparison with the neuropeptides CGRP and SP

This work presents new data concerning the immunohistochemical occurrence of the transient receptor potential vanilloid type-1 (TRPV1) receptor in the human trigeminal ganglion (TG) and spinal nucleus of subjects at different ontogenetic stages, from prenatal life to postnatal old age. Comparisons are made with the sensory neuropeptides calcitonin gene-related peptide (CGRP) and substance P (SP). TRPV1-like immunoreactive (LI) material was detected by western blot in homogenates of TG and medulla oblongata of subjects at prenatal and adult stages of life. Immunohistochemistry showed that expression of the TRPV1 receptor is mostly restricted to the small- and medium-sized TG neurons and to the caudal subdivision of the spinal trigeminal nucleus (Sp5C). The extent of the TRPV1-LI TG neuronal subpopulation was greater in subjects at early perinatal age than at late perinatal age and in postnatal life. Centrally, the TRPV1 receptor localized to fibre tracts and punctate elements, which were mainly distributed in the spinal tract, lamina I and inner lamina II of the Sp5C, whereas stained cells were rare. The TRPV1 receptor colocalized partially with CGRP and SP in the TG, and was incompletely codistributed with both neuropeptides in the spinal tract and in the superficial laminae of the Sp5C. Substantial differences were noted with respect to the distribution of the TRPV1-LI structures described in the rat Sp5C and with respect to the temporal expression of the receptor during the development of the rat spinal dorsal horn. The distinctive localization of TRPV1-LI material supports the concept of the involvement of TRPV1 receptor in the functional activity of the protopathic compartment of the human trigeminal sensory system, i.e. the processing and neurotransmission of thermal and pain stimuli.

Spatial and Temporal Brain Responses to Noxious Heat Thermal Stimuli in Burning Mouth Syndrome

Burning mouth syndrome (BMS) is an idiopathic orofacial pain condition. Although the pathophysiology of BMS is not clearly understood, central and peripheral neuropathic mechanisms are thought to be involved. The authors compared brain response to noxious heat stimuli in 16 right-handed women with primary BMS and 15 sex- and age-matched right-handed healthy female controls. A thermal stimulus sequence of 32 °C to 40 °C to 32 °C to 49 °C was repeated 4 times in a cycle. Warm and noxious heat stimuli were delivered with a Peltier thermode placed on the right palm or right lower lip for 32 s each in a session. Functional magnetic resonance imaging data were obtained by recording echoplanar images with a block design. Statistical Parametric Mapping 8 software was used to analyze the data. Patients and controls both reported feeling more pain during palm stimulation than during lip stimulation. Repetition of noxious heat stimulus on the lower lip but not on the palm induced habituation in brain activity in the cingulate cortex without reduction in pain perception. Multiple regression analysis revealed a correlation between perceived pain intensity and suppression of brain activity in the anterior cingulate cortex when the repeated thermal sequence was applied at the lower lip. Furthermore, the response of the parahippocampal area differed in BMS patients and controls when the same repeated thermal sequence was applied at the palm. The authors’ findings indicate that BMS patients show specific brain responses due to impaired function of the central and peripheral nervous systems (clinical trial registration: UMIN000015002).

Burning mouth syndrome: Current concepts

Burning mouth syndrome (BMS) is a chronic pain condition. It has been described by the International Headache Society as "an intra-oral burning or dysesthetic sensation, recurring daily for more than 2 h/day for more than 3 months, without clinically evident causative lesions." BMS is frequently seen in women in the peri-menopausal and menopausal age group in an average female/male ratio of 7:1. The site most commonly affected is the anterior two-thirds of the tongue. The patient may also report taste alterations and oral dryness along with the burning. The etiopathogenesis is complex and is not well-comprehended. The more accepted theories point toward a neuropathic etiology, but the gustatory system has also been implicated in this condition. BMS is frequently mismanaged, partly because it is not well-known among healthcare providers. Diagnosis of BMS is made after other local and systemic causes of burning have been ruled out as then; the oral burning is the disease itself. The management of BMS still remains a challenge. Benzodiazepines have been used in clinical practice as the first-line medication in the pharmacological management of BMS. Nonpharmacological management includes cognitive behavioral therapy and complementary and alternative medicine (CAM). The aim of this review is to familiarize healthcare providers with the diagnosis, pathogenesis, and general characteristics of primary BMS while updating them with the current treatment options to better manage this group of patients.

Peripheral nervous system involvement in primary burning mouth syndrome--results of a pilot study

OBJECTIVE

The pathophysiology of primary burning mouth syndrome (BMS) has remained enigmatic, but recent studies suggest pathology within the nervous system at multiple levels. This study aimed to investigate in detail the contribution of either focal or generalized alterations within the peripheral nervous system (PNS) in the etiopathogenesis of BMS.

SUBJECTS AND METHODS

Intraepithelial nerve fiber density (IENFD) of tongue mucosa was assessed in 10 carefully characterized BMS, and the results were compared to 19 age- and gender-matched cadaver controls, 6 with lifetime diabetes. Extensive neurophysiologic and psychophysical examinations of the trigeminal system and distal extremities were performed to profile PNS function in BMS.

RESULTS

Patients with BMS had significantly fewer intraepithelial nerve fibers (0,27, s.e. 0,18 mm(-1); P = 0.0253) than non-diabetic controls (0,92, s.e. 0,15 mm(-1)). In the subepithelial space, the amount of nerve fibers did not differ between the groups. The majority (9/10) of patients with BMS showed neurophysiologic or psychophysical signs of a more generalized PNS dysfunction.

CONCLUSIONS

Our results in neurophysiologically optimally characterized BMS patients confirm that pure focal small fiber neuropathy of the oral mucosa has a role in the pathophysiology of primary BMS. Furthermore, BMS may be related to a more generalized, yet subclinical peripheral neuropathy.

Thermal and mechanical quantitative sensory testing in Chinese patients with burning mouth syndrome--a probable neuropathic pain condition?

Background

To explore the hypothesis that burning mouth syndrome (BMS) probably is a neuropathic pain condition, thermal and mechanical sensory and pain thresholds were tested and compared with age- and gender-matched control participants using a standardized battery of psychophysical techniques.

Methods

Twenty-five BMS patients (men: 8, women: 17, age: 49.5 ± 11.4 years) and 19 age- and gender-matched healthy control participants were included. The cold detection threshold (CDT), warm detection threshold (WDT), cold pain threshold (CPT), heat pain threshold (HPT), mechanical detection threshold (MDT) and mechanical pain threshold (MPT), in accordance with the German Network of Neuropathic Pain guidelines, were measured at the following four sites: the dorsum of the left hand (hand), the skin at the mental foramen (chin), on the tip of the tongue (tongue), and the mucosa of the lower lip (lip). Statistical analysis was performed using ANOVA with repeated measures to compare the means within and between groups. Furthermore, Z-score profiles were generated, and exploratory correlation analyses between QST and clinical variables were performed. Two-tailed tests with a significance level of 5 % were used throughout.

Results

CDTs (P < 0.02) were significantly lower (less sensitivity) and HPTs (P < 0.001) were significantly higher (less sensitivity) at the tongue and lip in BMS patients compared to control participants. WDT (P = 0.007) was also significantly higher at the tongue in BMS patients compared to control subjects . There were no significant differences in MDT and MPT between the BMS patients and healthy subjects at any of the four test sites. Z-scores showed that significant loss of function can be identified for CDT (Z-scores = −0.9±1.1) and HPT (Z-scores = 1.5±0.4). There were no significant correlations between QST and clinical variables (pain intensity, duration, depressions scores).

Conclusion

BMS patients had a significant loss of thermal function but not mechanical function, supporting the hypothesis that BMS may be a probable neuropathic pain condition. Further studies including e.g. electrophysiological or imaging techniques are needed to clarify the underlying mechanisms of BMS.

Efficacy of low-level laser therapy for the treatment of burning mouth syndrome: a randomized, controlled trial

The aim of the present study was to assess the effect of low-level laser therapy (LLLT) in the treatment of burning mouth syndrome (BMS). A diode laser was used in 78 BMS patients who were randomly assigned into four groups: IR1W, n = 20 (830 nm, 100 mW, 5 J, 176 J/cm2, 50 s, LLLT weekly sessions, 10 sessions); IR3W, n = 20 (830 nm, 100 mW, 5 J, 176 J/cm2, 50 s, three LLLT weekly sessions, 9 sessions); red laser, n = 19 (685 nm, 35 mW, 2 J, 72 J/cm2, 58 s, three LLLT weekly sessions, 9 sessions); and control-group (CG), n = 19. Symptoms were assessed at the end of the treatment and eight weeks later; quality of life related to oral health was assessed using the Oral Health Impact Profile (OHIP-14). Statistical analysis was carried out using repeated measures analysis of variance followed by the posthoc Tukey test. There was significant reduction of the symptoms in all groups at the end of the treatment, which was maintained in the follow-up. The scores of the IR1W and IR3W laser groups differed significantly from those of the CG. There was also a decrease in the OHIP-14 scores in the four groups. The IR3W laser group scores differed significantly from those of the CG. LLLT reduces the symptoms of BMS and may be an alternative therapeutic strategy for the relief of symptoms in patients with BMS.

RNA-Seq Analysis of Human Trigeminal and Dorsal Root Ganglia with a Focus on Chemoreceptors

The chemosensory capacity of the somatosensory system relies on the appropriate expression of chemoreceptors, which detect chemical stimuli and transduce sensory information into cellular signals. Knowledge of the complete repertoire of the chemoreceptors expressed in human sensory ganglia is lacking. This study employed the next-generation sequencing technique (RNA-Seq) to conduct the first expression analysis of human trigeminal ganglia (TG) and dorsal root ganglia (DRG). We analyzed the data with a focus on G-protein coupled receptors (GPCRs) and ion channels, which are (potentially) involved in chemosensation by somatosensory neurons in the human TG and DRG. For years, transient receptor potential (TRP) channels have been considered the main group of receptors for chemosensation in the trigeminal system. Interestingly, we could show that sensory ganglia also express a panel of different olfactory receptors (ORs) with putative chemosensory function. To characterize OR expression in more detail, we performed microarray, semi-quantitative RT-PCR experiments, and immunohistochemical staining. Additionally, we analyzed the expression data to identify further known or putative classes of chemoreceptors in the human TG and DRG. Our results give an overview of the major classes of chemoreceptors expressed in the human TG and DRG and provide the basis for a broader understanding of the reception of chemical cues.