Figure 4.22 Except for the coated tongue, the clinical examination is within normal limit for this 42-year-old female patient complaining of burning sensations.
- Ordering complementary tests and referring for a consult depends on the degree of certainty for identifying burning mouth syndrome (BMS) by the ICHD-3 criteria and exclusion based on the history, review of system, and clinical examination.
- Chair-side assessment of the resting whole salivary flow rate: within normal limits with a flow rate of 0.4 mL/min (low normal rate value: 0.1 mL/min).
- Laboratory tests ordered for uncovering systemic factors: all results within normal limits.
- PHQ-4: normal with a score of 0 (scale 0–12).
- No evidence of local pathology, systemic, and psychological factors combined with the ICHD-3 criteria support a diagnosis of BMS.
- The ICHD-3 criteria define BMS on two aspects: one describing the clinical presentation and the other identifying the condition by the exclusion of local, systemic, or psychological pathologies.
- Overt clinical manifestations attributed to local factors and/or systemic conditions that may cause burning sensations preclude a diagnosis of BMS.
- In this case, the age and sex of the patient fall into the population mostly affected by BMS (please refer to Background Information box).
- The fact that the patient has daily burning mouth symptoms and denies any aggravation following food intake helped to rule out burning sensation caused by consumption/usage of certain foods or products: intermittent burning and dysguesia associated pine nut syndrome (Chinese Pinus armandii), allergic reaction to sorbic acid, cinnamon, nicotinic acid, propylene glycol, and benzoic acid.
- The possibility of a subclinical systemic condition or psychological etiology needs consideration before a final diagnosis of BMS is made.
- The overall treatment aims for any patients with BMS are: (1) reassure and inform about the condition; (2) relieve symptoms; and (3) give psychological and social support as needed.
- This lady, in otherwise good health, was bothered by the burning sensations but there was no sign of distress or anxiety related to her condition.
- Explanations were given regarding the occurrence of burning mouth sensations despite the normal appearance of intraoral tissues and the lack of local or systemic disorder. The same was done for the metallic taste.
- Any concern about mouth cancer wase addressed and clarified with the patient.
- She was informed that there was no treatment cure for BMS and the duration of the syndrome is highly variable and unpredictable.
- She was warned to pay attention to and avoid any traumatic habits she might have that can make symptoms worse.
- The treatment options were presented with emphasis on goals, benefits, disadvantages, duration of drug therapy, and follow-up.
- She agreed to do a topical treatment three times a day (t.i.d.) after each meal for 1 month with clonazepam. She was instructed to suck a tablet containing 1 mg of clonazepam while retaining the saliva in her mouth near the pain site for 5 min without swallowing and then expectorate.
- At 1-month follow-up visit, she reported improvement with the topical treatment modality. Recommendation was made to continue current medication regimen, monitor progression and side effects, and resume regular follow-up.
- In the case of no improvement with the recommended topical treatment, an alternative option included switching to systemic clonazepam 0.5 mg at bedtime (h.s.), monitor side effects, and continue regular follow-up.
- The clinical and laboratory findings, as well as the psychosocial assessment, leave no doubt as to the idiopathic nature of the burning mouth symptoms in this case.
- A diagnosis of BMS is most likely when the ICHD-3 criteria are fulfilled, laboratory findings are within normal limits, food intake eliminate the burning sensation, resting whole salivary flow is within normal limits, the score on the PHQ-4 that screens for anxiety and depression is below 3 or the score for the GAD-7 (anxiety) and PHQ-9 (depression) are each below 5.
- As no factors can predict how long the burning sensation will last, the patient was informed that remission occurs in approximately 50–60% of patients after a few months or years and that the symptoms can persist to some degree even with pharmacologic treatment.
- When no improvement is reported at follow-up with the selected drug treatment, another medication may be tried after discussion with the patient.
- CBT can be used alone and in combination with pharmacological therapy to improve treatment response.
- BMS is a chronic pain disorder characterized by burning sensation of the oral mucosa occurring in the absence of local, systemic, and psychological causes, often accompanied by subjective symptoms of mouth dryness and metallic taste.
- It is a distinctive nosological entity with poorly understood pathophysiology.
- Location of the burning is usually bilateral and independent of a nervous pathway.
- In most cases BMS starts on the tip of the tongue and may extend to the lateral border and other intraoral sites, most notably the palate and labial mucosa, but rarely to extraoral sites.
- The burning varies in intensity with no paroxysm and the patient may report an absence of burning on awakening that escalates throughout the day with peaking intensity in late afternoon/early evening.
- Sleep disturbance is infrequent.
- Many patients report disappearance of the burning with food intake or chewing but it resumes afterward and not infrequently the same happens with the metallic taste.
(Gurvits and Tan, 2013; Zakrzewska and Buchanan, 2016)
Terminology, prevalence, and incidence
- Former terms used to designate BMS in the literature are glossopyrosis, glossodynia, sore tongue, stomatodynia, stomatopyrosis, oral dysesthesia, and sore mouth.
- More recently BMS has also been called “burning mouth disorder” and “complex oral sensitivity disorder.”
- To emphasize its idiopathic nature BMS is also referred to as “primary or essential BMS.”
- Burning sensation that results from local, systemic, or psychological condition as confirmed by clinical examination and additional investigations is designated “burning mouth symptom” or “secondary BMS.”
- Prevalence data on BMS varies widely across studies, and this is mainly explained by the fact that most studies are based on self-report without physical examination; only a paucity of studies were conducted on a representative sample of the population, and different diagnostic criteria have been used.
- Cross-sectional population-based epidemiologic surveys indicate that 0.2–4% of adults report burning sensation not associated with oral lesions.
- BMS rarely occurs before the age of 30 and is more frequent amongst the elderly, with up to 90% of patients being peri- and postmenopausal women.
- The incidence rate of BMS adjusted for age and sex in a North American Caucasian population has been estimated at 11.4 per 100 000 person-years.
(Gurvits and Tan, 2013)
Etiology and pathophysiology
- The etiology of BMS remains unknown, and no causal relationship has been shown between depression and/or anxiety and BMS, although these patients are liable to anxiety and depressive state.
- Oral dryness is frequently reported by BMS patients; however, measurement of the whole resting salivary flow rate shows values above what seems critical for inducing burning sensation (0.1mL/min).
- Current evidence on pathophysiology favors a neuropathic background, but what the trigger is for the proposed mechanisms remains an unanswered question.
- Findings from psychophysical, electrophysiological, immunohistochemical, neuropathologic, and functional brain imaging studies indicate a complex pathophysiology involving heterogeneous neurological pathways at different level of the nervous system with the potential contribution of local environmental factors.
- The pathophysiological processes currently proposed for BMS are the following:
- Damage to the taste system carried by the facial (chorda tympani), glossopharyngeal, and vagus nerves leads to the loss of tonic inhibition of the trigeminal nerve and simultaneous dysfunction of the sensory components.
- Axonal degeneration in the epithelial and sub-papillary nerve fibers, which is responsible for a trigeminal small-fibers sensory neuropathy and dysfunction of the trigeminal pain pathway.
- Impairment of the central pain modulation pathway resulting from a presynaptic dysfunction of the nigrostriatal dopaminergic system.
- Drastic and concomitant changes in sources of steroids known to play a role in neuroregeneration and protection in the peripheral and central nervous system cause neurodegeneration and dysfunction of the trigeminal pain processes.
(Eliav et al., 2007; Woda et al., 2009; Jääskeläinen, 2012)