Circuit 2, station 8

Burning Mouth Syndrome (BMS) is a perplexing medical condition characterised by persistent burning pain localised to the oral mucosa, which exhibits no discernible abnormalities and endures for a minimum of four to six months. The aetiology of BMS remains elusive, confounding clinicians and researchers alike. A common hallmark of BMS is the concomitant alteration in gustatory perception, often manifesting as parageusia. This enigmatic disorder predominantly afflicts the female population, with a predilection for individuals in the peri-menopausal and post-menopausal stages. Diagnosis hinges largely on clinical criteria, necessitating the exclusion of other potential causes of oral discomfort and gustatory disturbances.

Emerging evidence suggests a multifaceted relationship between BMS and psychiatric comorbidities, encompassing both Axis I and Axis II psychiatric disorders. Additionally, structural and functional aberrations in the nervous system, as well as disturbances in the circadian rhythm, have been implicated in the pathophysiological underpinnings of BMS. The disruption of circadian rhythms can exert profound effects on pain perception and mood regulation, potentially impacting the functioning of the hypothalamic-pituitary-adrenal axis.

Lamey and Lewis have undertaken the categorisation of BMS into three distinctive types, predicated on the diurnal variation in the severity of symptoms experienced by afflicted individuals. Type 1 BMS typically manifests as symptom-free upon awakening, intensifying progressively throughout the day, often culminating in variable nighttime symptoms. Nutritional deficiencies and endocrine disorders, such as diabetes mellitus, have been postulated as potential contributors to this subtype. Type 2 BMS is characterised by constant symptoms throughout the day and has been associated with chronic anxiety. In contrast, Type 3 BMS presents with intermittent daytime symptoms interspersed with periods of symptom remission, with food allergy emerging as a plausible mechanistic factor.

The pathophysiology of BMS remains an intricate puzzle, with multiple theories postulated to explain its origins. Reduced oestrogen levels, frequently encountered in peri- and postmenopausal women, have been linked to atrophic changes in the oral mucosal tissue, rendering it more susceptible to inflammatory alterations and the subsequent development of BMS symptoms. Additionally, certain pathogens, including Candida, Enterobacter, Fusospirochetal, Helicobacter pylori, and Klebsiella, have exhibited a propensity to be more prevalent in individuals actively suffering from BMS. Diabetes mellitus, and its associated peripheral neuropathy, is another recognised source of BMS symptoms, primarily attributed to neuropathic mechanisms.

Various irritants have been implicated in the development or exacerbation of BMS, including dental materials such as mercury, amalgam, methyl methacrylate, cobalt chloride, zinc, and benzoyl peroxide. Furthermore, specific food allergies, including those triggered by peanuts, sorbic acid, chestnuts, and cinnamon, have been associated with BMS. Notably, BMS frequently co-occurs with neuropsychiatric conditions such as major depression, chronic anxiety, and mood disorders, with a particular predilection for comorbidity with major depressive disorder.

In addition to the factors mentioned above, orthodontic appliances, potential adverse effects of prescription medications, elevated levels of bradykinin, and comorbid dermatologic conditions have all been posited as potential contributing elements to the multifaceted landscape of BMS aetiology. BMS exhibits a pronounced gender bias, with a significantly higher prevalence in females, ranging from three to seven times that in males. Age also plays a pivotal role, with a strong association between advancing age and BMS prevalence noted in both genders. Prevalence peaks in females during the peri-menopausal and post-menopausal phases. Strikingly, BMS is virtually absent in children and rarely afflicts individuals below the age of 30. The overall prevalence of BMS remains inadequately documented but is tentatively estimated to approximate 4% of the population.

Diagnostic Challenges

The lack of consensus on BMS criteria compounds its diagnosis. Scala et al. proposed five clinical criteria, including daily deep and bilateral burning pain, pain duration of at least four to six months, constant or worsening pain throughout the day, improvement upon eating or drinking, and the absence of sleep interference. Additional criteria encompass taste disorders, xerostomia, sensory alterations, chemosensory changes, and mood or psychological disorders.

Evaluation

A comprehensive diagnostic approach is essential. Aravindhan, Vidyalakshmi, and colleagues advocate a structured evaluation encompassing:

1. A thorough history-taking and quantification of burning pain.
2. Oral mucosa examination to rule out local and systemic causes.
3. Assessment of psychological well-being.
4. Objective measurement of salivary rate and taste function.
5. Neurological examination and imaging to exclude degenerative disorders or neurological pathologies.
6. Oral cultures to identify suspected infections.
7. Allergy patch tests for allergic individuals.
8. Investigation for gastric reflux disease.
9. Screening for hormonal, autoimmune, and nutritional anomalies.

Importantly, biopsy is only indicated when oral lesions are visually detected.

Treatment and Management

Effective management of BMS is multifaceted and often requires a combination of modalities. Patients should be informed that complete symptom resolution is not always achievable.

Topical Medications:

• Capsaicin, an analgesic acting on sensory afferent neurons, demonstrates efficacy in managing neuropathic pain but may lead to transient increased burning sensation, dyspepsia, and toxicity.
• Topical clonazepam alleviates BMS symptoms, though it may result in dependence and side effects like dry mouth and fatigue.
• Unconventional topical agents, such as hot pepper and aloe vera gel, have shown promise in reducing symptoms.

Systemic Medications:

• Low-dose clonazepam is frequently prescribed, offering pain relief.
• Tricyclic antidepressants (TCAs), such as amitriptyline and nortriptyline, are employed despite causing xerostomia; selective serotonin reuptake inhibitors (SSRIs) like sertraline also yield improvement.
• Antipsychotic drugs, like amisulpride and levosulpiride, demonstrate symptom reduction during short-term treatment.
• Vitamin and mineral supplementation, such as B vitamins and folic acid, can lead to complete symptom resolution.
• Hormone replacement therapy may be considered for peri- and post-menopausal women.

Behavioural Modulation:

• Cognitive-behavioural therapy (CBT), encompassing relaxation techniques and cognitive restructuring, aids in symptom management.

Low-level Laser Therapy (LLLT):

• LLLT stimulates serotonin and β-endorphin production while reducing bradykinin secretion, thus mitigating burning symptoms. It also inhibits the depolarization of C fibres responsible for pain and heat stimuli transmission.