2.5 Burning Mouth Syndrome
By Gary D. Klasser, DMD, Certificate in Orofacial Pain (USA)
Burning mouth syndrome (BMS) is an enigmatic, idiopathic, chronic, often painful, clinical entity (condition). BMS does not have a well-established, universal, standardized, validated definition with field-tested classification systems or diagnostic criteria. It was first described by H. Fox in 1935. BMS has been called by various names depending on the quality and/or location of its intraoral pain presentation. Among the names are the following: glossodynia, glossopyrosis, glossalgia, stomatodynia, stomatopyrosis, sore tongue, burning tongue, scalded mouth syndrome, oral dysesthesia, burning mouth condition, and burning mouth syndrome. The use of multiple and heterogeneous labels shows the ambiguity and uncertainty that exists around BMS both within the scientific literature and in clinical practice. An unfortunate outcome of this approach is that it often produces a dilemma during the development and presentation of a definitive diagnosis while, at times, resulting in well-intentioned but misdirected interventions.
Because of the various definitions and multiple labels applied to BMS, it is easy to understand the frustration that people with BMS experience and the difficulties encountered by the clinician in evaluating and treating these individuals. This inauspicious situation exists because the patient is experiencing continuous burning intraoral pain that greatly affects their Quality of Life while the clinician is struggling to identify any obvious clinical signs, even with the accompaniment of additional diagnostic testing or imaging.
There is debate among researchers and clinicians as to whether burning mouth is truly a syndrome or a disorder. A syndrome (a disease unto itself) is a collection of several simultaneous signs and symptoms of varying intensity, which, in the case of BMS, is a normal-appearing oral mucosa with a burning sensation, a feeling of oral dryness, and taste disturbances. In contrast, a disorder is a condition with symptoms of other diseases such as dry mouth being the cause of the burning sensation often reported by BMS patients. This debate regarding semantics is rather academic, as BMS is most likely more than a singular disease process with multiple causes and abnormal bodily functions. Clinicians diagnose BMS by ruling out other diseases or conditions. This is called a diagnosis of exclusion.
Epidemiology. According to international studies, the prevalence (proportion of a population affected by a medical condition at a specific time) of BMS is believed to range from 0.7% to 15% of the general population depending on the methodology used for assessment (self-report questionnaire or clinical examination) and the diagnostic criteria utilized (continuous or episodic burning pain, presence or not of clinical lesions). Most of the data have been obtained from cross-sectional studies and convenience samples with heterogeneous compositions, whereas population-based information originated mainly from national surveys. Because of these imperfections and deficiencies, it is difficult to establish an “absolute” for the prevalence of BMS. The condition is most reported in postmenopausal women, generally in their 50s and 60s, and rarely before the age of 30 years. Men may also develop BMS with a reported ratio between approximately 1:5 and 1:7 compared to women, depending on the study population. Prevalence appears to increase with age in both men and women. Gender differences may be explained by biological, psychological, and sociocultural factors; however, these factors are yet to be defined. It appears from these epidemiological studies that menopausal females have a particularly high incidence of burning mouth. Nevertheless, despite these findings, no significant differences have been found between women with and without BMS in any of the following factors: number of years since menopause, occurrence of surgical menopause, use of hormone replacement therapy (HRT), years of treatment with HRT, and years passed since the completion of HRT. Only one study has been conducted on the prevalence of BMS in relation to ethnicity, and no studies have reported the prevalence of BMS by social, educational, or occupational groups.
Classification and Diagnostic Criteria. Several attempts have been made to develop an “ideal” classification system for BMS. It seems that the most practical approach in classifying cases of BMS is by dividing patients into either primary (essential or idiopathic) BMS (no other evident disease) or secondary BMS (oral burning from other clinical abnormalities). Because secondary BMS is associated with a preexisting condition or cause, it should be remembered that, once such a condition has been treated, the symptoms of BMS should either improve or disappear.
Over the years, several formal diagnostic criteria have been applied to BMS by individual researchers, clinicians, and various organizations. Unfortunately, despite similarities among some components of these criteria, there is no absolute consensus, nor has there been validation of any specific criteria. However, the most applied diagnostic criteria are as follows: intraoral burning pain or dysesthesia (an unpleasant abnormal sensation, whether spontaneous or evoked) recurring every day for more than two hours, for longer than 3 months, with no evident cause shown by clinical exams and/or investigations.
Clinical Signs and Symptoms. The clinical presentations of BMS are typically inconsistent and will vary from patient to patient. Patients often describe their oral symptoms with the following words: painful, burning, tender, tingling, hot, scalding and numbness; and sometimes the sensation is merely described as discomfort, raw and annoying. BMS is characterized by both positive (burning pain, altered taste, and uncomfortable sensation) and negative (taste loss and abnormal sensation) sensory symptoms. The burning is mainly located bilaterally (on both sides) and symmetrically in the front two-thirds of the tongue (71% to 78%), followed by the back and sides of the tongue (72%), the front of the bony roof of the mouth (25%), and the tissue lining the inside of the lips (24%), while often occurring in multiple sites. Other less commonly reported sites include the lining of the cheeks and back of the lips, the floor of the mouth, the hard and soft palates, and the throat (36%). Approximately 50% of BMS patients experience a spontaneous onset of symptoms without any identifiable triggering factor. However, about 17% to 33% of individuals with BMS attribute the onset of their symptoms to a previous illness such as an upper respiratory tract infection, previous dental procedure, or medication use (including antibiotic therapy), suggesting the possibility of neurologic alterations preceding the onset of burning in some patients. Other individuals claim that the onset of symptoms is related to traumatic life stressors. Typically, the symptoms occur continuously for months or years without periods of cessation or remission, with some reports suggesting an average duration of 2 to 3 years. There are reports of complete/partial remission (with or without intervention) in approximately 50% of patients and a complete spontaneous remission in approximately 20% of patients within 6 to 7 years of onset. (Tan 2020) The remission of symptoms, be it complete or partial, is often characterized by a change in pain pattern from a constant to an episodic form.
The pattern of daily symptoms is reportedly constant, with fluctuations in pain intensity and with approximately one-third of people with BMS experiencing symptoms during both wakefulness and sleep. Most individuals with BMS report minimal symptoms upon awakening, after which the symptoms gradually intensify during the day, becoming more aggravating toward the evening. About one-third of patients have difficulty with sleep onset, and some may awake during sleep as a result of the burning pain. The intensity of the burning pain has been described as moderate to severe, and in some cases, it is comparable to the intensity of toothache pain in regard to severity but not quality. In most individuals with BMS, the burning sensation intensifies in the presence of personal stressors; fatigue; and the intake of hot, spicy, and/or acidic foods. In about half of people with BMS, the intake of food or liquids and distraction seem to reduce or alleviate the symptoms. BMS patients have a significantly higher incidence of dry mouth, thirst, and taste disturbances, but they do not differ from healthy controls regarding changes in oral mucosa or dental problems. Those with BMS have more nonspecific health complaints (including sleep disturbances) and more severe menopausal symptoms as compared to healthy controls.
Etiology and Pathophysiology. Currently, the etiology (cause of a disease or condition) of BMS has remained largely unknown. The presumed etiology is best explained as the interaction between biological (neurophysiological mechanisms) and psychological and/or behavioral factors. Even though multiple local (physical, chemical, or biological), systemic, and psychological/behavioral factors have been found to be related to BMS, several of these factors should be considered as conditions important to the differential diagnosis (diagnosis of exclusion) of oral burning, rather than as etiological factors implicated in BMS.
Furthermore, it has been suggested that, to establish a causal link between two factors, one must have good consistency of data, meaning that the association investigated must be present in all cases regardless of the number of ways in which it is studied. For a biologically plausible explanation to exist, there must be transparency regarding how the potential etiological factor causes the outcome, and the suggested association must be independently verified. It appears that the current literature regarding BMS does not consistently meet these criteria.
The pathophysiology (i.e., the disordered physiological processes associated with disease or injury) of BMS continues to be unclear, especially with the lack of any visible oral mucosal changes upon examination. The current suggested pathophysiology is multifactorial and encompasses changes in taste; changes in hormone levels; nerve damage, dysfunction, dysregulation, and/or alteration, CNS changes, autoimmune disorders, and psychological factors.
Diagnosis. BMS has for many years remained a diagnosis of exclusion. A thorough medical and dental history, as well a review of systems and listing of all current medications, are essential for developing a definitive diagnosis. The history should include the patient’s description of their present concern, including a history of their symptom presentation, any associated symptoms, and a description of any previous and current treatments. The clinician should also elicit a measure of the intensity of the presenting pain using appropriate scales, as well as the character and distribution of the pain presentation. Factors that aggravate and lessen the pain should also be included in the history. Experiences regarding infections, diseases, and surgery should be ascertained. Questions should also be asked about dietary habits and the use of oral care products. An appropriate psychosocial history should also be considered as a component of the comprehensive history to determine the presence or status of any past or current psychosocial stressors.
Laboratory studies to rule out any local and systemic factors that may be responsible for the pain presentation will be guided by findings in the history and clinical examination. Testing for burning mouth pain may include studies of salivary flow and taste function, blood tests to rule out systemic factors, examinations of contact sensitivity and investigation for the presence of other biologic agents.
Adjunctive studies such as imaging should be considered if the pain presentation appears to be more complex, or atypical of the “normal” presentation. Such atypical presentations may include findings of sensory and/or motor disturbances, autonomic changes, or any other evidence suggestive of CNS pathology or neurodegenerative processes. Abnormalities or pathology of the salivary structures may also be identified through appropriate imaging studies. Measuring saliva flow may be used to determine if oral dryness is a key factor. Biopsy of the minor salivary glands may be a consideration if Sjögren’s syndrome is suspected. Psychometric testing may be indicated to evaluate the influence of psychological and/or anxiety factors. In some cases, evaluation for gastroesophageal reflux disease (GERD) may also prove helpful.
Management Strategies. Definitive recommendations for the management of BMS are somewhat lacking in the literature. From a clinical perspective, the clinician must initially determine if the patient is experiencing signs and symptoms consistent with primary (essential, idiopathic) BMS or secondary BMS, in which symptoms are due to underlying local or systemic conditions. Secondary BMS requires appropriate diagnosis and treatment of the underlying condition(s). In primary BMS, the etiology is unclear, so management options are based on a patient’s symptomatology.
Often, management involves a multidisciplinary team approach, often requiring multiple modifications of the management plan until an effective protocol is achieved. The importance of this approach cannot be overstated, as patients are often frustrated by a lack of understanding of this condition among clinicians. Currently, the clinician has a choice of three approaches or combinations thereof as considerations in management.
1. Behavioral Strategies. Behavioral strategies to be considered consist of self-help measures such as the cessation of parafunctional behaviors (clenching, bruxism, tongue protrusion) and/or the use of different oral care products, such as alcohol-free mouthwashes and products without flavoring agents or irritating components (e.g., cinnamic aldehyde, sodium lauryl sulfate, tooth-whitening agents, anticalculus ingredients). Other products that could be discontinued include mints, gum, or other breath aids. Stress management approaches such as moderate exercise regimens, yoga, and tai chi may be attempted. Additionally, desensitizing appliances may be considered to reduce oral burning or as a habit-breaking appliance. Behavioral strategies utilizing professional assistance include cognitive behavioral approaches (which focus on how beliefs and thoughts influence behavior) used alone or in combination with other therapies and/or group psychotherapy have also shown efficacy in decreasing pain intensity.
2. Topical Therapies. Many topical therapies (involving the application of medication directly to the skin or mucous membranes) have been trialed in the management of BMS. These range anywhere from anxiolytics and antidepressants to mucosal protectants, herbal supplements, and low-level laser therapy (photo biomodulation). Many of these therapies have reported variable success rates. However, few well-designed comparative studies have been performed, thus hampering recommendations developed from evidence-based decisions.
3. Systemic Therapies. Systemic approaches (in which medication travels through your blood to cells all over your body) to manage BMS have used a vast number of medications from various medication categories. Some of the treatments used include antianxiety drugs, antidepressants, anticonvulsants, and antioxidants all the way to acupuncture and transcranial magnetic stimulation. The spectrum of diversity of the various agents employed attests to the lack of definitive knowledge relating to the etiology and pathophysiology associated with BMS. Hence, there is very little consensus around the “gold standard” therapy of choice to guide the clinician in providing an evidence-based approach for the management of this difficult-to-manage condition.
Conclusion. Despite the current knowledge gained from the scientific literature, BMS continues to be a rather enigmatic, misunderstood, and underrecognized painful condition. Symptoms associated with BMS can be quite varied, thereby providing a challenge for clinicians while negatively impacting the patient. Management of this condition also continues to be a challenge, as it currently targets only symptom relief without a definitive cure. However, scientific inquiry and knowledge are advancing, and through more robust and rigorous scientific studies, the ability to uncover the mysteries associated with BMS will result in improved patient-tailored interventions.
