INTRODUCTION

Burning mouth syndrome (BMS) is an idiopathic painful condition manifested with burning sensations in the oral cavity in people with clinically normal oral mucosa and no identifiable local and/or systemic cause (1). Ten to fifteen percent of postmenopausal women have a history of burning in their mouth and these symptoms are most commonly reported 3-12 years after menopause (2). The prevalence of patients with BMS in general population is reported to be 0.7% - 7.9% (3). The underlying aetiology is still unknown, although the proposed underlying factors are classified as local (xerostomia, candidal infection), systemic (diabetic neuropathy, nutritional deficiencies - lack of serum iron, vitamin B1, B2, B6, B12 and folic acid), psychogenic and idiopathic (1, 3). Scala et al. (4) recommended a basic distinction between ‘primary BMS’ (true, idiopathic in which local or systemic cause cannot be identified), and ‘secondary BMS’ (caused by local or systemic disorder that can be treated) (1). In more than 60% of patients altered taste sensitivity (dysgeusia) is reported which indicates the possibility of damaged peripheral sensory neural mechanisms (2). BMS is also associated with psychological disorders, most commonly depression, but it remains unclear whether depression is a cause or consequence of chronic pain condition such as BMS (2). Burning symptoms are localized symmetrically (bilaterally), often isolated in the front third of the tongue, the lips, the palate, the pharynx, but the entire oral mucosa may be affected. Symptoms are spontaneous and present throughout the day, less pronounced in the morning, with a typical deterioration towards the end of the day, but with no discomfort during the night. Sleep is not affected (1). Burning symptoms subside with drinks and food intake, chewing gums and candies. Patients are often very concerned about their condition and they are generally anxious or upset (2). Cancerophobia is a common feature in BMS and is reported in 45% - 75% of the patients (5). The diagnosis of primary BMS is based upon exclusion of local and systemic conditions that may be associated with burning sensations of clinically normal oral mucosa (4).

Because of the unknown aetiology, there is still no proper treatment for BMS (1). Since the psychogenic factors are strongly associated with BMS symptomatology, psychological treatment, with or without other approaches is frequently used. Among these treatments, cognitive behavioural therapy, focusing on reducing the impact of dysfunctional cognitive factors (catastrophizing, anxiety, etc.) is the only psychological approach that has been confirmed as an effective treatment for BMS (3). Supportive therapeutic options such as topical capsaicin, low dose clonazepam, low-dose tricyclic antidepressants, and alpha lipoic acid are also available, but none of them can provide complete resolution of the symptoms (1).

Catastrophizing has been defined as an exaggerated negative orientation toward pain stimuli and pain experience (6). It consists of three sub components – rumination (“I worry all the time whether the pain will end”), magnification (“I wonder whether something serious might happen”) and helplessness (It’s awful and I feel it overwhelms me”). Catastrophizing affects the modulation of pain stimulus, the way patients cope with their pain, and the response to the treatment (7, 8). The Pain catastrophizing (PC) scale is a psychological instrument developed by Sullivan and Bishop which objectifies catastrophizing associated with pain (9).

The aim of this study was to examine the association between catastrophizing and clinical parameters of BMS, and to examine the association between catastrophizing and the quality of life in patients with BMS.

MATERIALS AND METHODS

The study was approved by the Ethics Committee of the School of Dental Medicine, University of Zagreb. Thirty patients diagnosed with primary BMS participated in the study. Informed consent was obtained from each patient. The criteria for the diagnosis of primary BMS were: burning sensations in clinically normal oral mucosa of min 3 months duration and the absence of any local and/or systemic factor that can lead to burning sensations in the oral cavity. Local and systemic factors were eliminated with the salivary flow rate measurement (10), complete blood count, serum iron, vitamin B12 and folic acid, and blood glucose levels. Exclusion criteria were the inability to understand the text of the informed consent and the presence of an identifiable local and/or systemic factor that could lead to burning sensation in the oral mucosa.

A questionnaire was given to all patients, after the diagnosis of primary BMS was established, but before the condition was explained and discussed with the patient. The questionnaire was completely anonymous and no personal data such as name, surname, date of birth, address, etc. was entered.

The questionnaire consisted of three parts. The first part included demographic and clinical parameters of the participating subjects (gender, age, duration of the symptoms, medications, subjective assessment of BMS impact on general wellbeing and previous treatment for BMS). For the subjective assessment of the BMS, the impact on general wellbeing - a three point scale (1 – significantly affects, 2 – affects, 3 – does not affect) was used. For the assessment of burning intensity, a 100 mm visual-analogue scale was used (0= no burning, 100= worst burning imagined). The second part of the questionnaire consisted of the Croatian version of the Oral Health Impact Profile Questionnaire 14 (OHIP-14) (11). Patients expressed their level of agreement with 14 questions about the oral health related quality of life, by choosing one of the answers: 0-never, 1-almost never, 2-sometimes, 3 often-and 4-very often. The third part of the questionnaire examined catastrophizing in pain using the Croatian version of the PC scale (12), where subjects expressed frequency of negative thoughts (presented in 13 statements) related to the burning in their mouth with one of the following answers: 0-not at all, 1-to a slight degree, 2-to a moderate degree, 3 – to a great degree, 4-all the time. The original PC scale assesses pain rather than burning sensation and the word “pain” is used throughout the scale. The participants were, therefore instructed to reflect only on burning in their mouth when reading the word “pain”.

Data were organized in Excel worksheets (Microsoft Excel, Microsoft Inc. U.S.) and statistically analysed using SPSS v20 software (IBM Inc, USA). Normality of the distribution was tested with the Smirnov Kolmogorov test. Chi-square test, Welch’s t test and analysis of variance were used to test intergroup differences when appropriate. Correlation between variables was assessed by Pearson correlation coefficient (r). The p values lower than 0.05 (p<0.05) were considered statistically significant.

RESULTS

Thirty patients participated in the study (25 women - 83.3% and 5 men - 16.7%). The average age of the patient was 66.1 ± 9.2 years. Other demographic and clinical characteristics of the patients are shown in Table 1.

No significant differences in demographic and clinical parameters between men and women were found.

Oral health related quality of life and pain catastrophizing are presented in Table 2.

No significant differences between men and women regarding the quality of life were found (p=0.385). There were no differences in quality of life between patients who were previously treated for BMS and those who were not previously treated for BMS (p=0.880). Patients who reported that BMS significantly affected their general wellbeing had lower quality of life than patients who reported that BMS affected their wellbeing and patients who reported that BMS did not affect their general wellbeing, respectively (p=0.005).

No significant differences neither in total catastrophizing score nor in the individual subcomponents of catastrophizing between women and men were found (p=0.244). Patients who reported that BMS significantly affected their general wellbeing had significantly higher scores of total catastrophizing and all three subcomponents of catastrophizing than patients who reported that BMS affected their general wellbeing and patients who reported that BMS did not affect their general wellbeing, respectively (p=0.002).

No significant differences in total catastrophizing score and individual subcomponents of catastrophizing between patients who were previously treated for BMS and patients who were not previously treated for BMS were found (p=0.913).

The association between catastrophizing, quality of life, intensity and duration of the symptoms is shown in Table 3.

Significant positive correlation was found between total catastrophizing and intensity of the symptoms and the quality of life, (r=0.538; r=0.694) respectively. Furthermore, significant positive correlation between all three subcomponents of catastrophizing and intensity of the symptoms and the quality of life was also found, respectively. No significant correlation between catastrophizing and duration of the symptoms was found.

DISCUSSION

BMS is a chronic painful condition for which there is still no adequate treatment (13). Therefore, it is not surprising that BMS can cause an increase in negative emotional states such as depression, anxiety and catastrophizing and have negative impact on the quality of life (3, 14).

Pain Catastophizing Scale has a maximum score of 52, which is obtained by summing the values associated with the reply to each of the 13 statements (15). According to the authors, score above 40 presents clinically significant catastrophizing that requires psychological intervention. Out of the 30 patients in this study, 9 of them (30%) had a total score above 40, indicating a significant psychological impact that BMS has on almost one third of the patients. According to Matsuoka et al. (3) catastrophizing is a major dysfunctional cognitive factor in Japanese patients with BMS. Average catastrophizing score in this study was 28.4 ±15 which is similar to the catastrophizing score in Japanese patients with BMS which was 28.19 ± 9.70 (3). Rumination was the most emphasized subcomponent of catastrophizing amounting to 10.2 ± 5 out of maximum 16 points (63.8%). Magnification and helplessness were somewhat less emphasized, amounting to 6.9 ± 3.4 out of maximum 12 points (57.5%) and 11.2 ± 7.4 out of maximum 24 points (46.7%). The fact that rumination is very strong in this population is further supported by the finding that the questions which obtained highest scores in OHIP-14, were related to the self-consciousness and psychological discomfort (“Have you been self-conscious because of your teeth or mouth?” and “Have you felt tense because of problems with your teeth or mouth?”). This is not surprising since symptoms in BMS were reported to be of moderate intensity (5.8 ± 2), present during the whole day with the average duration of 22 months. In a long period of more or less constant pain, it is expected that the patients will start ruminating about their condition generating frustration and other negative emotions.

All three subcomponents as well as total catastrophizing score significantly correlated with the intensity of the symptoms. On the other hand, no significant correlation was found between the duration of the symptoms and catastrophizing score, indicating that patients can cope with chronic pain for a long time provided the intensity is low.

Total catastrophizing score as well as all three subcomponents positively correlated with OHIP-14 scores. This finding suggests strong association between catastrophizing and quality of life in BMS patients. This is not surprising: patients who express negative thoughts about their condition and feel helpless are more likely to have lower quality of life than patients who try to maintain their normal daily functioning and cope with their condition. Similar results were reported in a Japanese BMS population as well as in other chronic pain conditions such as fibromyalgia, rheumatoid arthritis, osteoarthritis and postherpetic neuralgia (16-18). It is still unclear whether catastrophizing is a cause or consequence of chronic pain. Recent studies indicate that catastrophizing is associated with impaired regulation of endogenous pain-inhibitory opioids (19).

Why is catastrophizing important in BMS patients? It is necessary to have an insight into the patient's catastrophizing for several reasons. As stated earlier, catastrophizing affects the patient's experience of pain and the way patients cope with their pain (8, 19). Furthermore, catastrophizing is a better predictor of response to treatment than factors such as pain intensity, medication consumption, knowledge of the painful condition, depression, anxiety, etc. (7, 16).

In conclusion, measurement of catastrophizing in BMS patients may help in identifying individuals with negative behavioural patterns in whom additional psychological intervention (except for basic information about the condition provided by the oral medicine specialist) could reduce / eliminate negative cognitive factors and improve coping with chronic painful condition such as BMS.