Burning mouth syndrome

What is burning mouth syndrome (BMS)?

Burning mouth syndrome (BMS) is known by many names including oral dysaesthesia, glossopyrosis, stomatodynia, stomatopyrosis and glossodynia among others. It has classically been described by the International Headache Society in 2004 as “an intra-oral burning sensation for which no medical or dental cause can be found.”

It is a common problem that can affect up to 15% of adults overall. The clinical diagnosis is made by the following criteria:

• daily and deep bilateral burning sensation of the oral mucosa;
• burning sensation for at least 4-6 months;
• constant intensity or increasing during the day;
• possible improvement on eating or drinking;
• an absence of interference with sleep.

What is/are the causes of burning mouth syndrome?

BMS seems to have a predisposition in peri-/post-menopausal women, although it can affect anyone. Risk factors included female gender, depression, anxiety and chronic medical conditions including gastrointestinal and urogenital diseases. There are certain hormonal changes in peri-menopausal women that are thought to be contributory.

It may be secondarily related to issues including thyroid disease, psychiatric illnesses, oral infections, certain medications, dental treatment, vitamin and/or mineral deficiencies, but is most commonly regarded as “idiopathic”. This means that there is no particular underlying cause that can be identified and that it is a “diagnosis of exclusion”, i.e. once underlying causes are ruled out the focus is on treating the symptoms rather than explaining it.

BMS is considered to be neuropathic, meaning that the theory is an issue with nerve conduction. It remains unclear however, whether central or peripheral mechanisms are involved. Biopsies from the tongue in some studies have shown loss of epithelial nerve fibres and changes on MRI have been shown, with some studies suggesting a decrease of endogenous dopamine. Studies have furthermore shown significant differences in thermal (temperature) and nociceptive (painful) responses in patients with BMS.

Evidence exists for an immunologic cause with allergies being demonstrated to a range of dietary antigens including sorbic acid, cinnamon, nicotinic acid, propylene glycol and benzoic acid. Sodium lauryl sulphate, a substance in many toothpastes that enable them to “foam”, may also be contributory.

What are the symptoms?

BMS can cause a range of symptoms including a “stinging” or “burning” sensation, often exacerbated by certain foods (e.g. spicy foods) and/or products (e.g. certain toothpastes). Classically, the symptoms are better in the morning, worsen throughout the day and then subside at night. Commonly patients report a dry mouth (xerostomia) and/or a bitter or bad taste (dysgeusia), as well as the classic “burning” sensation.

Generally, all patients report pain or burning, with 63% reporting dry mouth, 60% a bitter or metallic taste and 35% report altered taste perception. Pain can be described as “burning”, “scalding”, “tingling” or “numbness”. Symptoms most commonly involve the tongue and may be paradoxically improved during eating.

What investigations will be done?

The first priority is a thorough clinical examination to ensure that the oral mucosa is normal and healthy, with no identifiable pathological lesions or co-existing issues. This is done under direct vision and will also encompass an examination of the neck lymph nodes and major salivary glands by palpation.

In some instances, a flexible nasendoscopy (FNE) will be warranted, passing a small camera through the nose to examine the upper aerodigestive tract (nasopharynx, oropharynx and laryngopharynx).

Blood tests maty be requested to exclude underlying causes such as vitamin B12 deficiency, folic acid deficiency, iron deficiency, zinc deficiency, anaemia, hypothyroidism, renal disease, diabetes and autoimmune conditions such as Sjogren’s syndrome among others.

Rarely, allergy testing may be beneficial in a small number of patients, with an opinion sought from an immunologist.

What treatments are available?

There is a varied evidence base in the scientific literature for treatments.

Perhaps the most important element of treatment is a careful and clear explanation that nothing sinister or concerning is driving the symptoms. Patients are often concerned that they may have oral cancer, and reassurance that the examination and investigations have proven normal can provide a degree of closure to patients.

Clearly, correction of any underlying driver for secondary BMS (e.g. low serum folate, hypothyroidism, diabetes, etc.) is of paramount importance in achieving a resolution to symptoms.

In the absence of any cause (idiopathic BMS), talking therapies such as Cognitive Behavioural Therapy (CBT) can be helpful in engendering acceptance and living with a chronic pain that cannot be otherwise explained, a frustrating situation for patients that can impact upon quality of life.

Medications can include Difflam® (benzydamine hydrochloride) spray for topical anaesthesia. This can be supplemented with a number of different drugs including low dose tricyclic antidepressants (e.g. amitriptyline, nortriptyline), benzodiazepines (e.g. clonazepam) and/or anticonvulsants/anti-epileptic medications (e.g. gabapentin). More recently, the focus has shifted on other antidepressants (e.g. venlafaxine) and/or the nutritional supplement alpha lipoic acid. Finally, alternative topical agents can be used that are stimulatory (e.g. capsaicin) and hormone replacement therapy (HRT) where warranted can be beneficial.

Alpha lipoic acid is a nutritional supplement that can be bought from health food shops and is commonly taken at a dose of 200mg three times daily. It has shown some superiority over placebo in some studies, although the evidence base is mixed. Side effects can include heartburn and headache.

Clonazepam lozenges can be used for topical effect (0.5mg to 1mg sucked 1-4 times/day and expectorated) but can show systemic absorption with side effects including drowsiness, dry mouth, euphoria and dependence.

Antidepressants have shown some promise, with a study of the selective serotonin reuptake inhibitor (SSRI) paroxetine demonstrating 80% of patients experiencing overall pain reduction, including 36% of patients reporting complete remission after twelve weeks of incremental treatment.

Drugs will often have side effects that can outweigh the benefits of treatment in milder cases. Ideally topical anaesthesia, dietary adjustments and psychological therapies can be the preferred treatment modality for this reason.

What can I do to reduce my symptoms?

It is worth keeping a diet diary of foods that might be identified as precipitating symptoms, such that these can be avoided (provided this does not interfere with adequate nutritional intake as part of a balanced diet). You can consider trialling a toothpaste that does not contain sodium lauryl sulphate (SLS), as this has been identified in some studies as contributory to BMS, as well as conditions that can mimic the symptoms.

Relaxation, yoga, meditation and mindfulness can also reduce associated stress and anxiety, as can regular aerobic exercise. These can have a beneficial impact on holistic sense of wellbeing and, in turn, reduce the severity of symptoms from BMS.