Perception of stimulus size in patients with burning mouth syndrome

Co-occurrence of Pain Symptoms and Somatosensory Sensitivity in Burning Mouth Syndrome: A Systematic Review

Background

Burning mouth syndrome (BMS) is a chronic and spontaneous oral pain with burning quality in the tongue or other oral mucosa without any identifiable oral lesion or laboratory finding. Pathogenesis and etiology of BMS are still unknown. However, BMS has been associated with other chronic pain syndromes including other idiopathic orofacial pain, the dynias group and the family of central sensitivity syndromes. This would imply that BMS shares common mechanisms with other cephalic and/or extracephalic chronic pains. The primary aim of this systematic review was to determine whether BMS is actually associated with other pain syndromes, and to analyze cephalic and extracephalic somatosensory sensitivity in these patients.

Methods

This report followed the PRISMA Statement. An electronic search was performed until January 2015 in PubMed, Cochrane library, Wiley and ScienceDirect. Searched terms included “burning mouth syndrome OR stomatodynia OR glossodynia OR burning tongue OR oral burning”. Studies were selected according to predefined inclusion criteria (report of an association between BMS and other pain(s) symptoms or of cutaneous cephalic and/or extracephalic quantitative sensory testing in BMS patients), and a descriptive analysis conducted.

Results

The search retrieved 1512 reports. Out of these, twelve articles met criteria for co-occurring pain symptoms and nine studies for quantitative sensory testing (QST) in BMS patients. The analysis reveals that in BMS patients co-occurring pain symptoms are rare, assessed by only 0.8% (12 of 1512) of the retrieved studies. BMS was associated with headaches, TMD, atypical facial pain, trigeminal neuralgia, post-herpetic facial pain, back pain, fibromyalgia, joint pain, abdominal pain, rectal pain or vulvodynia. However, the prevalence of pain symptoms in BMS patients is not different from that in the age-matched general population. QST studies reveal no or inconsistent evidence of abnormal cutaneous cephalic and extracephalic somatosensory sensitivity.

Conclusions

There is no evidence for a high rate of other pain symptoms or somatosensory impairments co-occurring with BMS. These results thus suggest that BMS rather depends on specific mechanisms, likely at the trigeminal level. Nevertheless, more thoroughly conducted research is required to draw definitive conclusion.

Evidence of chorda tympani dysfunction in patients with burning mouth syndrome

BACKGROUND

More than two-thirds of patients with burning mouth syndrome (BMS) have altered taste sensation. The authors conducted a study to assess chorda tympani and trigeminal nerve function in these patients.

METHODS

The study was composed of 48 patients; 22 were diagnosed as having BMS, 14 had burning symptoms related to other diseases and were diagnosed as having secondary burning mouth syndrome (SBMS), and 12 were healthy volunteers. The authors evaluated the electrical detection thresholds of the infraorbital and mental nerves and the electrical taste and electrical detection/tingling thresholds in the anterior two-thirds of the tongue for all patients. Electrical taste threshold is thought to be dictated by chorda tympani nerve function while electrical detection/tingling thresholds are regulated by trigeminal nerve function.

RESULTS

The mean electrical taste/tingling detection thresholds ratio and the taste detection thresholds were significantly higher in patients with BMS than in patients with SBMS and in control subjects, indicating chorda tympani nerve dysfunction. Eighteen (82 percent) of the 22 patients with BMS demonstrated chorda tympani dysfunction (13 unilateral and five bilateral).

CONCLUSIONS

Chorda tympani hypofunction may play an important role in BMS pathology. Unilateral hypofunction may be sufficient to produce generalized burning sensation exceeding the affected nerve area.

CLINICAL IMPLICATIONS

Elevated taste detection threshold levels determined via electrogustatory testing and an elevated taste/tingling detection thresholds ratio may assist clinicians in the diagnosis of BMS. More studies are needed to validate these findings.

Relationship between oral sensitivity and masticatory performance

The size of a bolus determines how it will be manipulated in the mouth and swallowed. We hypothesized that mucosal sensitivity would be important for masticatory function. The accuracy of solid object size perception, spatial acuity, and food particle size reduction during mastication were measured in 22 healthy adults with/without topical anesthesia of their oral mucosa. Topical anesthesia had no effect on the perception of sphere sizes, but significantly reduced spatial sensitivity. Without anesthesia, there was a correlation between an individual's ability to perceive the sizes of steel spheres (diameter, 4-9 mm) and the sizes of food particles chewed for 15 cycles and at swallowing. There was no correlation between spatial sensitivity and food particle size. We suggest that the stimuli used to test two-point discrimination stimulates only superficial receptors, which involve light touch and are easily anesthetized, while the spheres might excite more deeply-set receptors. The latter appear to be more important for masticatory performance and swallowing.

Update on burning mouth syndrome: overview and patient management

Burning Mouth Syndrome (BMS) is a chronic pain syndrome that mainly affects middle-aged/old women with hormonal changes or psychological disorders. This condition is probably of multifactorial origin, often idiopathic, and its etiopathogenesis remains largely enigmatic. The present paper discusses several aspects of BMS, updates current knowledge, and provides guidelines for patient management. There is no consensus on the diagnosis and classification of BMS. The etiopathogenesis seems to be complex and in a large number of patients probably involves interactions among local, systemic, and/or psychogenic factors. In the remaining cases, new interesting associations have recently emerged between BMS and either peripheral nerve damage or dopaminergic system disorders, emphasizing the neuropathic background in BMS. Based on these recent data, we have introduced the concepts of "primary" (idiopathic) and "secondary" (resulting from identified precipitating factors) BMS, since this allows for a more systematic approach to patient management. The latter starts with a differential diagnosis based on the exclusion of both other orofacial chronic pain conditions and painful oral diseases exhibiting muco-sal lesions. However, the occurrence of overlapping/overwhelming oral mucosal pathologies, such as infections, may cause difficulties in the diagnosis ("complicated BMS"). BMS treatment is still unsatisfactory, and there is no definitive cure. As a result, a multidisciplinary approach is required to bring the condition under better control. Importantly, BMS patients should be offered regular follow-up during the symptomatic periods and psychological support for alleviating the psychogenic component of the pain. More research is necessary to confirm the association between BMS and systemic disorders, as well as to investigate possible pathogenic mechanisms involving potential nerve damage. If this goal is to be achieved, a uniform definition of BMS and strict criteria for its classification are mandatory.

The influence of density and material on oral perception of ball size with and without palatal coverage

The size of a bolus determines how it will be manipulated in the mouth and swallowed. Ten healthy individuals assessed the size of ball bearings of five sizes (4-11 mm diameter) and four materials with different densities in order to investigate the effect of weight on oral size perception. To study the role of the tongue and palate, the experiment was performed with and without a custom-made plastic palate. The results revealed that size itself determines size perception, and that material and weight are negligible factors. An illusional effect in the direction of under-estimation was found for the ball bearings, especially for the small sizes up to 8 mm diameter. While wearing a plastic palate a significant improvement (P<0.05) occurred; the participants performed better and there was less under-estimation. An explanation for this could be that only a minor part of the total area of the ball bearing touches the palate and is hence detected, while the tongue alone is more compliant and thereby able to sense the ball's whole size.

Differences in the oral size illusions produced by cross-modality matching of peg and hole stimuli by the tongue and fingers in humans

Individuals overestimate the diameter of 1-mm-deep stimulus holes presented to the tongue when they use their fingers to select a hole of matching diameter. The aim here was to determine whether the oral size illusion evident for 1-mm-deep holes would also occur with 1-mm-high pegs of similar diameters. The illusion was studied in 24 individuals who were blindfolded during the trials. The two sets of test stimuli were (a) 5 cylindrical pegs (1 mm high) and (b) five circular holes (1 mm deep), each of 2.5, 5.0, 7.5, 10.0, 12.5 mm dia. The stimuli were held to the mouth with one hand, while the fingers of the free hand were used to select a matching object from a comparator series of either 1-mm-deep holes or 1-mm-high pegs ranging from 2.0 to 18 mm dia. Each stimulus was presented four times in a random order. The participants overestimated the diameter of the 1-mm-deep stimulus holes when these were matched with 1-mm-deep comparator holes. However, there was no illusion with four out of five 1-mm-high stimulus pegs when matched with 1-mm-high comparator pegs. In the 'reverse' experiment, there was no illusion with four out of five stimulus holes when these were matched with 1-mm-high comparator pegs. However, an illusion was evident for all the 1-mm-high stimulus pegs when these were matched with the 1-mm-deep comparator holes. Regardless of the nature of the stimulus ('hole' or 'peg'), a mismatch between the stimulus and comparator was consistently seen only when the fingers probed comparator holes. The oral size illusion is not due to any intrinsic differences in the sensitivities of the tongue or fingers. Rather, the illusion is due to the inability of the fingertip to access small comparator holes.

Oral mucosal blood flow in patients with burning mouth syndrome

The pathophysiology of burning mouth syndrome (BMS) is largely unknown. Thus, the aim was to study oral mucosal blood flow in BMS-patients using laser Doppler flowmetry (LDF). Thirteen BMS patients (11 female, two male; mean age+/-SD 64.3+/-7.9 years, mean disease duration 18.9+/-6.2 months) and 13 healthy non-smoking controls matched for age and gender (11 female, two male; mean age 64.7+/-8.1 years) were investigated. Using the LDF technique mucosal blood flow (mBF) was measured at the hard palate, the tip of the tongue, on the midline of the oral vestibule, and on the lip. Measurements were made at rest and over 2 min following dry ice application of 10 s duration using a pencil shaped apparatus. In addition, blood pressure (BP), heart rate (HR), peripheral cutaneous blood flow, and transcutaneous pCO(2) were continuously recorded. Mucosal blood flow (mBF) increased at all measurement sites in response to dry ice application (P<0.001) with peak flow at 0.5--1.5 min after stimulation onset. During the following 1.5--2 min, blood flow decreased at all sites with a tendency to return to baseline towards the end of the observation period. Except for BP and peripheral blood flow, all of the cardiovascular changes exhibited significant changes during the observation period; no differences between groups were detected. When compared to healthy controls BMS patients generally exhibited larger changes in mBF. These changes were significant for recordings made on the hard palate (F[1,24]=13.9, P<0.001). Dry ice stimulation appears to be an effective, non-invasive and reasonably tolerable means to investigate mucosal blood flow at different mucosal sites. In general, vasoreactivity in BMS patients was higher than in healthy controls. BMS patients exhibited a higher response on the hard palate compared to controls. These changes in oral blood flow appear to be specifically related to BMS symptoms indicating a disturbed vasoreactivity.

The effect of stimulus form and dimensions on the oral size illusion in humans

Previous work has shown that individuals overestimate the diameter of holes presented to the tongue when they use their fingers to select matching holes from a range of comparators. This disparity is known as the oral size illusion. The hypothesis that this illusion arises from the greater pliability of the tongue surface compared with that of the fingertip was tested here. Two experiments were carried out on 64 participants. In experiment 1 (n=32), the stimuli were two sets of holes, 1 and 5 mm deep and 2.4, 5.6, 8.2, 12 mm dia. , which were presented to the tongue. The comparator was a series of holes 5 mm deep and 0.8-15 mm dia., which were explored manually. Participants significantly overestimated all diameters of the 1- and 5-mm deep stimulus holes (p<0.05). Apart from the 2.4-mm dia. holes, there were no significant differences between the illusions produced with the holes 1 mm and 5 mm deep (p0.7). In experiment 2 (n=32) individuals were tested with small cylinders ('pegs') 1 mm high and 2.6, 5.2. 7.6, 12.6 mm dia. and also with the four 5-mm deep stimulus holes used in experiment 1. The 'peg' stimuli presented to the tongue were matched against a similar set of 1-mm pegs, 2-18 mm dia., explored with the fingers. The comparator series for the 5-mm deep holes was the same as for experiment 1. Participants consistently overestimated the size of the 5-mm holes (p<0.001). However, there was no illusion with the peg stimuli (p=0.08), except for the 7.6-mm dia. stimulus (p<0.05). The results of experiment 1 did not support the experimental hypothesis that the oral size illusion was due to the greater pliability of the tongue surface. The result of experiment 2 suggests that the oral size illusion does not occur when peg stimuli are used instead of holes. The form and diameter of the stimulus is thus important in determining the magnitude of the oral size illusion.