This study revealed that the prevalence of oral burning disorder in the patients who referred to the oral medicine department of Shiraz dental school between the years 2007 and 2015 was 8.5%. And only 25 patients, from the 2 533 records evaluated, had idiopathic oral pain or primary BMS (0.98%). This finding is suggestive that BMS is an uncommon disease. This clinic has the most referrals for oral and maxillofacial medicine patients in Shiraz, so almost all patients seeking help for oral symptoms were referred to this clinic during these years.
Recent articles which use the latest theories of possible etiologic factors leading to BMS show a range of 1% to 40% prevalence for this disorder. The epidemiology of BMS is imprecise in literature because of the wide range of definitions and diagnostic criteria. Most studies investigate the cause of oral burning pain rather than idiopathic BMS (
3, 4, 14, 15). The concept of a pragmatic approach in dividing BMS into primary (idiopathic) and secondary (with a known cause) was first introduced by Scala et al. ( 11) and supported by others in the literature ( 3, 4). In the secondary group with evident etiologic factors leading to this painful sensation, local, systemic, and psychological factors may be responsible ( 2- 4).
Overall, local factors were the main reasons for which the evaluated patients of this population were seeking oral care. Systemic diseases such as diabetes mellitus were the next cause of oral burning and psychological factors were next in ranking. Idiopathic BMS or primary burning mouth syndrome was the least common form.
Among the local factors evaluated, oral lesions listed in
Table 1 accounted for approximately 30% of the patients. Oral mucosal diseases such as lichen planus, benign migratory glossitis, hairy tongue, and fissured tongue have been previously proposed as causative factors of BMS (3, 4). Fortunately, oral mucosal diseases are all associated with visual clinical findings and can be easily diagnosed from BMS patients in whom the oral mucosa appears normal. The diagnosis of oral lesions is usually based on meticulous clinical and laboratory investigations by oral medicine experts.
Oral infections were, also, common in this population. In general, a high prevalence of candidal infection is reported in patients that complain of oral burning (
3, 4). For ruling out this fungal infection, detecting signs of atrophy, erythema, and ulcer in the oral mucosa is helpful. Also, patients who have candidal infections usually experience pain upon eating, whilst BMS pain is commonly aborted in this situation. This confirms that fungal infection is not the source of pain in primary BMS patients ( 16). Moreover, viral and bacterial infections are, also, proposed as causes of oral burning ( 17, 18). But, a “hit and run” theory is mentioned especially for viral infections, because no active infection exists in most cases, only elevation of viral IgM antibodies in the serum are detected ( 18).
Allergic reactions account for 7.4 % of the patients evaluated in this study. Allergic contact stomatitis is a common source of oral pain. Food allergens, dental restoration alloys, and chemical materials in dental products are all implicated in symptoms of oral burning (
19, 20). Eliminating the causative factor is the best solution for separating allergic reactions from BMS pain.
Trauma due to ill-fitting dentures or parafunctional activities of the oral cavity emerged as an explanatory factor for burning sensation of the mucosa as can be seen in the results of this study and other reports (
21). Local erythema is observed in patients with ill-fitting dentures, but there is no support on the fact that mechanical trauma causes BMS ( 21). Oral parafunctional habits such as bruxism are chiefly associated with anxiety; but to this point of time, there are no studies that support the fact that these habits can cause BMS ( 22).
Only 2% of the studied population had burning pain that was due to oral dryness as a result of a local complication in the salivary glands and 4.4% due to xerostomia as a result of a systemic diseases. There is contradictory evidence on the incrimination of xerostomia in developing BMS. Reports indicate that oral burning is often concomitant with oral dryness and targeting factors associated with oral dryness may help alleviate an oral burning complaint. A high prevalence of 34% to 39% of this symptom is, also, reported for BMS patients (
21, 23). It is true that a lack of lubrication in the oral mucosa results in pain often of burning quality. But, the complaint of dry mouth can be related to a change in the quality and the composition of saliva rather than its quantity ( 4).
Systemic factors emerged as a strong explanatory factor for oral burning and were seen in 20% of the studied population. Among these factors, endocrine disorders were the most frequent etiologic factors. Uncontrolled diabetes and hypothyroidism are known causes of oral burning (
17, 21). The relationship between diabetes and BMS is explained as a peripheral neuropathy due to metabolic changes in the mouth. This state, also, generates a hypofunction of the salivary glands and subsequent saliva reduction which also promotes burning sensation of the oral mucosa ( 3, 24).
There are a number of drugs that are incriminated in the development of BMS among which angiotensin converting enzyme inhibitors (eg, captopril, enalapril, lisinopril), diuretic and beta blockers are mainly involved. There is a dose-dependent and duration of treatment association between the use of drug and the onset of the disease (
25). In the present study, we found that 7% of the patients complaining of burning pain were consumers of these certain drugs.
Nutritional deficiencies were responsible for the burning symptom in 3.4% of the patients complaining of pain in this study. Vitamin deficiencies, iron deficiency anemia, and zinc deficiency are known systemic factors that cause burning sensation (
3). There is no report on the prevalence of this symptom in patients with deficiencies aforementioned. And the exact mechanism by which these nutritional deficiencies can lead to the onset of oral burning remains hidden. Vitamin B complex replacement therapy, however, often proves ineffective for pain relief ( 11). Further population studies are needed to relate this matter.
The link between BMS and psychological disorders dates back to the early 1920s. Depression, personality disorders such as hypochondria, somatization, anxiety, and cancer phobia are listed as major factors associated with BMS (
3, 4, 14, 26). The prevalence of these disorders ranges from 20% to 52 % in the literature ( 4). In the present retrospective study, the prevalence is 5.4% and known cases of psychological disorders that were under medical treatment could be solely included. But previous case-controlled studies have used different psychological screening tools to detect these disorders. Therefore, undiagnosed cases were, also, detected and included in the results ( 14, 26). However, many have stated that the determination between the development of BMS following psychological disorders or preceding burning symptom is not clear ( 26). Also, studies have revealed that there are no significant differences in personality profiles between BMS patients and control healthy subjects, concluding that BMS with no etiologic factor is different from burning mouth in psychogenic patients ( 27). Furthermore, many medications used in psychological conditions cause dry mouth and taste alterations that can present as burning sensation ( 26). So the dilemma remains whether BMS or chronic pain precipitates psychological disturbances or vice versa.
8.4% of the subjects had oral burning with no evident clinical cause or, in other words, primary BMS. A neuropathic basis is now accepted for BMS with the possibility of a dysfunction at the peripheral or central arc path and the processing of cortical excitation (
5, 28). Latest studies uncover that a deficiency in the control of pain could be in part the cause of BMS and that BMS and dysgeusia conditions are not linked to similar structural changes in the brain ( 29). Whereas the reports of 2016 still express that there is a lack of universal definition of BMS and its characteristics and that the exact pathophysiology of primary BMS remains unknown ( 2, 30).
Glossodynia together with pain in the floor of the mouth was the most prevalent form of pain in the present cross sectional study. This form of pain is mostly seen in patients with local disease and psychological disorders as the cause of pain. Whereas generalized burning was the most common form of pain in older patients that had a history of certain systemic diseases. The location of pain had an interestingly equal number for the tongue and generalized involvement in patients with idiopathic primary oral burning (BMS). This is in accordance with the population-based study of the incidence of primary or idiopathic BMS by Kohorst et al. which reports tongue as the most common site of burning and after that the burning of several sites in the oral cavity (
8). There are reports of a few rare cases of only lips or palate burning sparing other anatomic locations of the oral mucosa in BMS ( 8, 14). It is obvious that systemic disorders cause generalized pain, but the generalized pain or the involvement of tongue whilst sparing other sites in idiopathic BMS needs more population-based studies for confirmation.
The apparent association of gender, age, and menopause with idiopathic BMS has long been confirmed (
4, 8, 18). This is in accordance with our findings which reveal that primary BMS patients had a significant higher mean of age compared to the patients with evident etiologic factors. Also, female gender accounted for approximately 75% of the patients complaining of the symptom. It should be kept in mind that during perimenopause, an increase in salivary phosphate concentration, protein, Na +, K +, Ca 2+, and Mg 2+ is seen. Also, hormonal changes lead to chronic anxiety and stress ( 3). These can all be a reason for the burning sensation of the oral cavity with no evident clinical explanation in this group of patients. Although there is a probability that men are more reluctant than women to visit a physician and seek help for a symptom.
Of note, the third edition of the international classification of headache disorders in 2013 describes BMS as a recurrent daily pain for more than 2 hours per day for more than 3 months with a burning quality that is felt superficially in the oral mucosa (
1). Not considering this definition is a shortcoming of this study, but whilst using data gathered before 2013, this was inevitable. Even though these criteria are not specifically used as diagnostic criteria in the present study, it is unlikely that many cases of BMS were erroneously included.
Nonetheless, it would be misleading to conclude that these percentages are completely valid for the general population. The complete records of only 7 years of the referring patients were available for this study. Possibly a wider duration of time and a greater population study can lead to more reliable conclusions. Shiraz dental school was the only center with the referral of oral mucosal disease in Fars province in the years of 2007 to 2015, and it was the only center in this province where oral and maxillofacial medicine specialists practiced in. There were probably patients that suffered from this pain but did not seek an oral and maxillofacial specialist for their problem, so this is not a general study. But it is an estimation of the prevalence of this problem in one province of Iran. Furthermore, a unique method was not used for the diagnosis of every etiology, although every case was definitively diagnosed by either an oral medicine specialist or a physician who used a reliable method of diagnosis as listed in
Table 1. And also, more exact description of the symptoms such as pain intensity and duration of pain can, also, be helpful in understanding and managing BMS patients who lacked the records that were evaluated for this population.
In conclusion, according to the description of primary BMS which is defined as a pathologic condition that causes burning sensation in an otherwise healthy individual, the diagnosis of BMS can be considered one of exclusion. For the treatment of this disorder which is a major challenge for the practitioners, identifying possible causative factors is the first step. Based on the available evidence, it is difficult to differentiate between primary and secondary BMS. Even so, it is judicious for clinicians treating BMS to recognize possible local, systemic, and psychological etiologies that may be responsible for oral burning pain and, in turn, reach a diagnosis that helps manage the patient’s symptoms appropriately. Hence, substantial delay is avoided and appropriate treatment strategies are initiated.