Trigeminal small-fiber sensory neuropathy causes burning mouth syndrome

"Burning tongue" and "burning tip": the diagnostic challenge of the burning mouth syndrome

OBJECTIVE

To investigate the clinical features of burning mouth syndrome (BMS) in a large cohort of patients and to correlate them with the results of tongue biopsy.

METHODS

We screened 98 patients complaining of oral burning pain for at least 6 months. Forty-two patients were excluded after screening for contact sensitivity to dental materials, food allergies, tongue injuries, malignancies, connective tissue and metabolic disorders, oral infectious diseases, vitamin deficiencies, and other systemic diseases known to cause neuropathy. Fifty-six patients underwent neurologic examination and assessment of pain intensity, depression, anxiety, quality of sleep, and quality of life. Tongue biopsy with the quantification of epithelial nerve fibers (ENF) was performed in 51 patients.

RESULTS

Compared with 9 healthy participants (4.13+/-1.85 SD), epithelial innervation density was significantly reduced in 38 patients (1.35+/-1.46 SD; P<0.0001) and normal in 13 patients (6.1+/-2.19 SD). The clinical features differed in the two groups: patients with reduced ENF density complained of pain in the whole tongue, lips, hard palate, and alveolar ridges, reported dysgeusia and xerostomia in 29% of cases (P<0.001), and 24% of them were depressed. Patients with normal innervation complained of pain on the tip of the tongue, reported dysgeusia and xerostomia in 7.7% of cases, and 54% of them were depressed (P<0.017).

DISCUSSION

The diagnostic criteria for BMS are not defined yet and the relationship with depression and anxiety is debated. We proposed a biopsy-supported approach for the diagnosis. Our study shows that BMS can present with two distinct clinical pictures and that tongue biopsy can contribute to the assessment of the diagnosis. Mood disorders occur frequently and should be considered when approaching patients and treatment options. These observations could help physicians in identifying patients with BMS and addressing them with the appropriate diagnostic work-up and treatment.

A case of unilateral burning mouth syndrome of neuropathic origin

The neuropathic origin of a case of unilateral burning mouth syndrome, previously diagnosed as psychogenic, was ascertained by intra-oral mucosa biopsy, which showed a severe sensory fibers damage, probably caused by maxillary anesthetic block and dental surgery.

Sensory purinergic receptor P2X3 is elevated in burning mouth syndrome

Recent studies show that P2X(3) may play a role in neuropathic pain, including orofacial pain. Burning mouth syndrome (BMS) is a chronic neuropathic pain condition affecting 0.6-12% of post-menopausal women in the Western world. This study evaluates, for the first time, P2X(3) immunoreactivity levels in lingual mucosa in BMS patients. Patients diagnosed with BMS (n=9) in accordance with International Association for the Study of Pain criteria and patients attending for wisdom tooth removal (n=10, controls), were involved in this study. A pain history and score was recorded on a visual analogue scale (VAS) prior to obtaining a lingual biopsy. Immunohistochemistry and image analysis were used to quantify submucosal nerve fibres expressing P2X(3) and the structural marker neurofilaments. P2X(3) positive fibres were significantly increased in BMS compared with controls (p=0.024). In contrast, neurofilament-staining fibres were reduced in BMS, and when expressed as a ratio of the neurofilament percentage area, there was a trend for an increase of P2X(3) positive fibres in the BMS group. Increased P2X(3) immunoreactivity in the trigeminal sensory system may play a role in the symptoms observed in BMS. P2X(3) may therefore be a therapeutic target for treating BMS and trigeminal neuropathic pain.

Idiopathic ophthalmodynia and idiopathic rhinalgia: two topographic facial pain syndromes

OBJECTIVE

To describe 2 topographic facial pain conditions with the pain clearly localized in the eye (idiopathic ophthalmodynia) or in the nose (idiopathic rhinalgia), and to propose their distinction from persistent idiopathic facial pain.

BACKGROUND

Persistent idiopathic facial pain, burning mouth syndrome, atypical odontalgia, and facial arthromyalgia are idiopathic facial pain syndromes that have been separated according to topographical criteria. Still, some other facial pain syndromes might have been veiled under the broad term of persistent idiopathic facial pain.

METHODS

Through a 10-year period we have studied all patients referred to our neurological clinic because of facial pain of unknown etiology that might deviate from all well-characterized facial pain syndromes.

RESULTS

In a group of patients we have identified 2 consistent clinical pictures with pain precisely located either in the eye (n=11) or in the nose (n=7). Clinical features resembled those of other localized idiopathic facial syndromes, the key differences relying on the topographic distribution of the pain.

CONCLUSIONS

Both idiopathic ophthalmodynia and idiopathic rhinalgia seem specific pain syndromes with a distinctive location, and may deserve a nosologic status just as other focal pain syndromes of the face. Whether all such focal syndromes are topographic variants of persistent idiopathic facial pain or independent disorders remains a controversial issue.

Effect of lingual nerve block on burning mouth syndrome (stomatodynia): a randomized crossover trial

Burning mouth syndrome (stomatodynia) is associated with changes of a neuropathic nature the main location of which, peripheral or central, remains unknown. A randomised, double-blind crossover design was used to investigate the effects of lingual nerve block on spontaneous burning pain and a possible correlation with the effects of topical clonazepam, the patient's response to a psychological questionnaire, and the taste and heat thresholds. The spontaneous burning was measured with a visual analogue scale (VAS) just before and 15 min after injection. The decreases in VAS score after lidocaine or saline injection were not significantly different (2.7+/-3.9 and 2.0+/-2.6, respectively; n=20). However, two groups of patients could be identified: in a "peripheral group" (n=10) the VAS decrease due to lingual nerve injection was 4.3+/-3.1cm after lidocaine and 0.9+/-0.3 cm after saline (p=0.02). In a "central group" (n=7), there were an increase in pain intensity score (-0.8+/-2.6 cm) after lidocaine and a decrease (1.5+/-3.0 cm) after saline (p=0.15). An increase in the hospital anxiety and depression (HAD) score and a decreased taste sensitivity and heat pain threshold of painful oral area were seen in patients compared with age-and-sex-matched controls (p<0.05). Topical clonazepam treatment tended to be more effective (p=0.07) and HAD score lower (p<0.03) in the peripheral than in the central group. These results suggest that the neuropathic disorder associated with stomatodynia may be predominantly peripheral, central or mixed depending on the individual. Topical application of clonazepam and HAD may serve as indicators of which mechanism is dominating.

Smell and taste disorders in polyneuropathy: a prospective study of chemosensory disorders

OBJECTIVE

The aim of the study was to assess the occurrence and the frequency of chemosensory dysfunction in patients with polyneuropathy (PNP).

METHODS

We performed a prospective observational study. Olfactory function was assessed using the standardized 'Sniffin' Sticks' test to measure odor threshold for phenyl ethyl alcohol, odor discrimination, and odor identification. Gustatory function was assessed using the standardized 'taste strips' test. In addition, we assessed etiology, neurophysiology, and severity of the PNP, and the patients' comorbidities and medication.

RESULTS

A total of 53 consecutive patients were enrolled (15 women, 38 men; mean age 61 years); 27 of them (51%) exhibited olfactory dysfunction and 23 of them (43%) gustatory dysfunction. Patients with diabetic PNP had significantly lower taste scores than patients with inflammatory, genetic, or idiopathic PNP. In addition, odor identification was negatively correlated with PNP severity.

CONCLUSION

The applied bedside tests are useful to detect chemosensory dysfunction in patients with PNP. Chemosensory dysfunction is quite frequent in these patients.

Self-reported severity of taste disturbances correlates with dysfunctional grade of TMD pain

Altered central neural processing of sensory information may be associated with temporomandibular disorders (TMD) pain. The objectives of this study were to compare the prevalence of self-reported taste disturbances in TMD pain patients and in a control population, and to determine whether frequency of taste disturbances was correlated with dysfunctional grade of TMD pain. Subjects were 2026 people within a German population sample and 301 consecutive TMD patients diagnosed using the Research Diagnostic Criteria. Taste disturbances were measured using two questions from the Oral Health Impact Profile. Dysfunctional grade of TMD pain was measured with the Graded Chronic Pain Scale. A two-sample test of proportions revealed that TMD patients reported a greater frequency of taste disturbances, 6%, than did the general population subjects, 2% (P < 0.001). Moreover, the frequency of taste disturbances correlated with the dysfunctional grade of TMD pain. For each 1 unit increase in taste disturbance, the odds of observing a higher grade of TMD pain increased by 29% (95% CI: 3-63%, P = 0.03). Analysis by individual taste question and adjustment for age and gender did not substantially affect the results. These findings are consistent with a central neural dysfunction in TMD pain and suggest that a common neural substrate may underlie sensory disturbances of multiple modalities in chronic pain patients. Further research regarding taste disturbances and trigeminally mediated pains such as in TMD is warranted.

Response of human oral mucosa and skin to histamine provocation: laser Doppler perfusion imaging discloses differences in the nociceptive nervous system

OBJECTIVE

To investigate the existence of histamine-excitable nerve fibers in the oral mucosa and to compare the response to histamine provocation in healthy volunteers with that in a small group of patients with chronic oral pain.

MATERIAL AND METHODS

Thirteen healthy volunteers and six patients suffering from chronic oral pain took part in the study. Blood perfusion was monitored in the hard palate, the tongue, and the skin of the cheek using laser Doppler perfusion imaging (Perimed; Sweden). Baseline scannings were performed, followed by 15 scannings after iontophoresis of histamine (1%). A free description of the sensations was then obtained from the participants after finishing the measurements.

RESULTS

Compared to pre-histamine scanning, histamine application resulted in a considerable increase in blood perfusion in all regions (p<0.001) that was significantly higher in skin than in oral mucosa (p<0.001). There were no significant differences between the healthy volunteers and the patients regarding baseline blood flow, increased blood perfusion, or flare size after histamine provocation. The sensory impression was reported to be more persistent and intense in the skin than in the oral mucosa. No effect on mucosa could be detected by visual inspection.

CONCLUSIONS

Intra-oral flare could be induced by activating histamine-excitable nerve fibers. Both duration and intensity of the flare were considerably less pronounced than in the control skin site. Histamine application was not clearly associated with itch.

Burning mouth syndrome

Burning mouth syndrome (BMS) is a chronic disease characterized by burning of the oral mucosa associated with a sensation of dry mouth and/or taste alterations. BMS occurs more frequently among postmenopausal women. The pathophysiology of the disease is still unknown, and evidence is conflicting; although some studies suggest a central origin, others point to a peripheral neuropathic origin. The efficacy of some medications in the treatment of BMS suggests that the dopaminergic system may be involved.

An open-label, noncomparative, dose escalation pilot study of the effect of paroxetine in treatment of burning mouth syndrome

OBJECTIVE

The objective of this study was to evaluate the effectiveness and tolerability of paroxetine in patients with burning mouth syndrome (BMS).

DESIGN

In a 12-week open-label, noncomparative, prospective study, 71 subjects with primary BMS were assigned to receive an initial dosage of paroxetine (10 or 20 mg/day). The dosage was increased to a maximum of 30 mg/day. Of these patients, 52 were available to examine the efficacy of treatment in this study.

RESULTS

The cumulative proportion of responders was 80.8% (42/52). Of those responding, complete remission of pain was observed in 70.4% (19/27) of patients by week 12. The effects of paroxetine were dose-dependent. The incidence of adverse reactions for the initial daily dosage of 10 mg (41%) was significantly lower than that for 20 mg (76%) (chi(2) test). No serious safety issues were observed.

CONCLUSION

About 80% of BMS patients experienced pain reduction with 12 weeks of paroxetine treatment with only minor transient side effects. These results suggest that paroxetine may be useful in the treatment of patients with BMS.

Serum interleukin-6 in patients with burning mouth syndrome and relationship with depression and perceived pain

Objective. To examine alteration of serum interleukin-6 and its clinical significance in burning mouth syndrome (BMS) patients. Methods. 48 BMS patients and 31 healthy controls participated in the study. Serum interleukin-6 was measured by means of ELISA. Hamilton rating scale of depression (HRSD) and visual analogue scale (VAS) were used to quantitiate depressive status and pain levels of subjects, respectively. Results. 15 (31%) patients displayed substantial depressive symptoms (HRSD ≧ 16). HRSD scores of patients were significantly higher than controls and positively correlated to their VAS values (P = .002). Serum interleukin-6 in patients was much lower than controls and negatively correlated to their VAS values (P = .011). However, no significant relations were found between interleukin-6 and HRSD scores (P = .317). Conclusions. Serum interleukin-6 in patients with burning mouth syndrome is decreased and negatively correlated to chronic pain. Both psychological and neuropathic disorders might act as precipitating factors in BMS etiopathogenesis.

Skin biopsy for the diagnosis of peripheral neuropathy

Skin biopsy has become an accepted tool for investigating small nerve fibres, which are invisible to conventional neurophysiological tests even though they are affected early on in peripheral neuropathies of varying aetiology. Morphometric analysis of epidermal and dermal nerves has proved to be reliable, reproducible and unaffected by the severity of neuropathy, making skin biopsy useful for diagnosing small fibre neuropathy (SFN) in clinical practice. The possibility of obtaining skin biopsy specimens from different sites of the body, to repeat them within the area of the same sensory nerve, to distinguish between somatic and autonomic nerves and to investigate the expression of nerve-related proteins has widened the potential applications of this technique to clinical research. Skin biopsy performed using a minimally invasive disposable punch is a safe and painless procedure. Using specific antibodies with bright-field immunohistochemistry or immunofluorescence technique, it is possible to investigate unmyelinated fibres innervating the epidermis of hairy and glabrous skin, large myelinated fibres supplying specialized corpuscles in glabrous skin, and autonomic fibres innervating sweat glands, blood vessels and arrector pilorum muscles. This review discusses the features of skin innervation in hairy and glabrous skin, the functional properties of skin nerve fibres and their changes in peripheral neuropathies.

Overexpression of artemin in the tongue increases expression of TRPV1 and TRPA1 in trigeminal afferents and causes oral sensitivity to capsaicin and mustard oil

Artemin, a member of the glial cell line-derived neurotrophic factor (GDNF) family, supports a subpopulation of trigeminal sensory neurons through activation of the Ret/GFRalpha3 receptor tyrosine kinase complex. In a previous study we showed that artemin is increased in inflamed skin of wildtype mice and that transgenic overexpression of artemin in skin increases TRPV1 and TRPA1 expression in dorsal root ganglia neurons. In this study we examined how transgenic overexpression of artemin in tongue epithelium affects the anatomy, gene expression and calcium handling properties of trigeminal sensory afferents. At the RNA level, trigeminal ganglia of artemin overexpresser mice (ART-OEs) had an 81% increase in GFRalpha3, a 190% increase in TRPV1 and a 403% increase in TRPA1 compared to wildtype (WT) controls. Myelinated and unmyelinated fibers of the lingual nerve were increased in diameter, as was the density of GFRalpha3 and TRPV1-positive innervation to the dorsal anterior tongue and fungiform papilla. Retrograde labeling of trigeminal afferents by WGA injection into the tip of the tongue showed an increased percentage of GFRalpha3, TRPV1 and isolectin B4 afferents in ART-OE mice. ART-OE afferents had larger calcium transients in response to ligands of TRPV1 (capsaicin) and TRPA1 (mustard oil). Behavioral sensitivity was also exhibited by ART-OE mice to capsaicin and mustard oil, measured using a two-choice drinking test. These results suggest a potential role for artemin-responsive GFRalpha3/TRPV1/TRPA1 sensory afferents in mediating sensitivity associated with tissue injury, chemical sensitivity or disease states such as burning mouth syndrome.

Subgemmal neurogenous plaque associated with burning tongue: report of two cases and review of the literature

Subgemmal neurogenous plaques, biphasic structures with a neurofibroma and neuroma patterns, are observed in tongue biopsies involving subepithelial areas, being characterized as aggregates of nerve plexus and ganglion cells. Oral burning symptoms, having many possible causes, are commonly observed during oral medicine practice, but the association of subgemmal neurogenous plaque with tongue burning symptoms is very unusual. Reported here are two cases of focal burning sensation in the lateral border of the tongue diagnosed as subgemmal neurogenous plaque through biopsy. Recognizing this entity is important to avoid misdiagnosis of other neural proliferations, especially in cases involving focal tongue burning.

Burning mouth syndrome responsive to pramipexol

Burning mouth syndrome (BMS) is characterized by burning discomfort or pain in otherwise normal oral mucosa. It is usually refractory. Treatment modalities are scarce. Herein we report one case of primary disabling BMS, previously refractory to multiple regimens, with complete and persistent improvement with pramipexol, a nonergot dopamine agonist which has high selectivity for dopaminergic D2 receptors. We discuss potential pathophysiological implications of our findings.

Skin biopsy as a diagnostic tool in peripheral neuropathy

Skin biopsy is a safe, minimally invasive, painless and cheap tool for providing diagnostic information on small nerve fibers, which are invisible to routine neurophysiological tests. Biopsy can be performed in hairy skin to investigate unmyelinated and thinly myelinated fibers and in glabrous skin to examine large myelinated fibers. Morphometric analysis of skin nerves is readily accomplished through the use of immunohistochemical techniques, and has proved to be reliable, reproducible and unaffected by the severity of neuropathy. One further advantage of skin biopsy over conventional nerve biopsy is that it allows somatic nerve fibers to be distinguished from autonomic nerve fibers. Morphological changes, axonal degeneration and abnormal regeneration occur in cutaneous nerves very early in the course of peripheral neuropathies, making skin biopsy a promising tool for investigating the progression of neuropathy and the effect of neuroprotective treatments in clinical practice and trials. This article reviews the techniques that are used to investigate the innervation of human skin, the possible uses of skin biopsy in diagnosing and monitoring peripheral neuropathies, and correlations between skin biopsy findings and those of other diagnostic methods.

Use of topiramate for glossodynia

INTRODUCTION

Glossodynia is a multifunctional disorder characterized by painful sensations in the mouth and throat and especially on the tongue. It is commonly cured by long-term therapy with systemic regimens of anxiolytics, antidepressants, and anticonvulsants.

CASE

We report here the case of a 65-year-old woman with a 4-month history of glossodynia. Clinical and laboratory evaluations performed the diagnosis of idiopathic glossodynia, and several treatments with carbamazepine and then with gabapentin induced the development of serious adverse reaction. Only treatment with topiramate has been able to induce a complete improvement of symptoms.

DISCUSSION

The pathogenesis of idiopathic glossodynia remains unclear, since it recently has been suggested as a possible neuropathic basis of burning mouth syndrome, demonstrating an altered excitability in the trigeminal nociceptive pathway at peripheral and/or central nervous system level. The various mechanisms of topiramate, which act at different neural transmission levels, blocking sodium and calcium channels, enhancing GABA concentration, and decreasing glutamate function at postsynaptic site, may explain the effects of topiramate in our patient.

CONCLUSION

Therefore, we suggest that topiramate could represent a useful therapeutic option in the treatment of glossodynia.

[Primary and secondary stomatodynia: a difficult diagnosis]

Primary stomatodynia involves mainly women after menopause presenting somatization, depression and anxiety at values higher than control subjects. This chronic pain is often an intense burning pain beginning in the tongue the entire oral cavity, increasing in intensity through the day with a high level of emotional after effects. These patients often describe two associated symptoms: mouth dryness sensation and altered taste. The causes remain uncertain. The participation of female sexual hormones and neuropathic factors has been suggested possibly through a sensory neuropathy of small fibers of the oral mucosa. Normal clinical examinations and non clinical tests differentiate primary from secondary stomatodynia. The management consists in using low doses of topical clonazepam without swallowing or systemic clonazepam. The association of this drug with tricyclic antidepressants has given variable results. A cognitive behavioural management has been successfully attempted.