Chemosensory Dysfunction, Oral Disorders and Oral Health-related Quality of Life in Patients With Primary Sjögren's Syndrome: Comparative Cross-sectional Study

Comparative Cross-sectional Study

Mirjana Šijan Gobeljić; Vera Milić; Nada Pejnović; Nemanja Damjanov

Disclosures

BMC Oral Health. 2020;20(187) 

In This Article

Discussion

The reported data about the associations between chemosensory disturbances, BST, halitosis and OHRQoL in patients with SS are limited. The present study demonstrates that patients with pSS have impaired olfactory and gustatory functions, burning sensation of the tongue (BST) and poor OHRQoL in comparison with the healthy controls without sicca symptoms. We found similar frequencies of halitosis among patients with pSS and the healthy controls. Our findings are in agreement with other studies showing disturbed taste and smell functions in patients with SS.[5,6,30,31]

In our study, gustatory dysfunction was more frequently found in patients with pSS than olfactory dysfunction. This finding is consistent with some studies,[5,6,31] but contradictory to one report.[30] A possible explanation for this discrepancy may be related to the different methods for testing smell function. In our study, detection of cognitive smell function was performed by a smell identification test, whereas in the study by Kamel et al.[30] the chemosensory threshold (which reflects peripheral sensory impairment) was assessed. An ideal testing method for smell function would include threshold assessment, detection and identification tests. However, only identification test was performed in our study. Our findings demonstrate that dysgeusia, BST and halitosis were often reported among patients with pSS, which is in line with the reported data.[6] In contrast, no differences were found in the occurrence of halitosis between pSS and the control group in our study.

There are indications that smell and taste impairments, as well as the burning sensation in the mouth may be caused by hyposalivation.[5,13,32] However, some studies show that salivary factors are not responsible for impaired taste performance.[32] A recent study showed lower rates of salivary secretion in patients with pSS, but only a weak correlation was found between salivary secretion rates and the presence of oral disorders. This observation implies that oral disorders are not caused by low salivary flow.[6]

We observed relatively high percentage of ageusic and hypogeusic patients within the group of patients with pSS. While ageusia is a rare condition that accounts for less than 1% of patients with chemosensory dysfunction,[33–35] the patients with pSS in this study were classified as ageusic as they experienced the inability to taste basic tastes: sweetness (34%), sourness (11%), saltiness (10%) or bitterness (19%). Interestingly, between 40 and 50% of healthy controls were found to be hypogeusic. However, the number of patients with pSS with ageusia/hypogeusia was significantly higher compared to healthy controls.

As for olfactory function, anosmia is the most common complaint of patients with chemosensory disorders.[13,31,33] However, in our study 3.8% of the patients with pSS were categorized as anosmic and 36.5% as hyposmic. The proportion of anosmic patients in our study was lower than in the study by Rusthen et al.,[6] in which 12.9% of patients with pSS were classified as anosmic. The main reasons why we chose to use Sniffin' Sticks was because they had already been used in clinical practice and available data from the literature.[6] We applied general hygienic measures to prevent any contamination and we strictly followed the regular recommended procedure of positioning the pens under the subject's nose, approximately 2 cm from either nostril, for a maximum of 4 s. However, having in mind that the most widely used smell test in the world the University of Pennsylvania Smell Identification Test (UPSIT) has become a 'gold standard' in olfactory testing, we shall consider its use in our future research. Approximately half of the patients with anosmia and hyposmia experience changes in food preferences resulting in higher consumption of sugar and seasonings.[33–35] Moreover, their loss or reduced ability to taste affect their eating habits.[36] The patients with chemosensory disorders could either increase or reduce food intake, which may result in an increase or a decrease in their body mass.[35]

About half of the patients with pSS complained of BST, while none of healthy controls experienced BST. BST in patients with pSS was mainly related to food intake. Burning sensation in the mouth is frequently found in patients with SS.[9] More than half of the patients with pSS had dysgeusia with distorted taste of bitterness occurring on daily basis, while dysgeusia was reported by less than 10% of healthy controls. The occurrence of dysgeusia and burning sensations in the tongue and mouth in patients with pSS is underestimated and the data about the frequency and severity of these disorders are scarce. In our study we found higher proportion of ageusic and hypogeusic patients with pSS, in comparison to the data from other studies.[33–35] The patients with pSS in our study were categorized as ageusic if they had experienced loss of sense of basic tastes: sweetness (34%), sourness (11%), saltiness (10%) or bitterness (19%). Disagreement with the results of other studies suggests that taste impairments in patients with pSS need to be more thoroughly addressed in future studies. Oral disorders occurred on a daily basis in a large proportion of patients with pSS in our study. This finding highlights the need for more attention to chemosensory disorders in patients with this disease.

Possible underlying cause of high occurrence of olfactory and gustatory dysfunctions in patients with pSS could be systemic inflammatory response such as overexpression of interferon–inducible genes.[37] Toll-like receptor pathways and interferon pathways mediate the inflammatory responses in taste tissue in pSS and may interfere with normal taste transduction and taste-bud cell turnover.[38]

Oral malodor has been receiving increasing attention over the last decade. In the present study, a third of the patients with pSS complained of halitosis, whereas similar proportion of healthy controls reported oral malodor. The main oral causes of this disorder and effective treatment strategies are known.[39] However, it has been reported that a third of the patients seeking treatment for halitosis do not actually have oral malodor caused by the production of volatile sulphur compounds, therefore they cannot be categorized as 'genuine halitosis' patients.[12] This could explain rather high proportion of healthy controls complaining of halitosis in our study.

Chemosensory and oral disorders, burning mouth syndrome in particular, usually reduce the patients' quality of life, and 'psychological dysfunction' is common in patients with this diagnosis.[40] Consistent with this finding, the present study shows poor OHRQoL as estimated by OHIP-14 score in patients with pSS. The OHIP-14 questionnaire is designed to examine only certain aspects of OHRQoL, so an improved questionnaire is needed to obtain a more accurate evaluation of chemosensory disorders and OHRQoL in patients with pSS.[6]

A recently published meta-analysis by Al-Ezzi et al.[41] supplies data from five studies which included 378 patients with pSS. This study provides an assessment of the impact of dryness caused by primary SS on smell, taste and sexual function in female patients, and influence on their quality of life. After a systematic literature review, the authors concluded that pSS has a negative impact on smell, taste, sexual function and quality of life in female patients with pSS.

A most recent study demonstrated significantly high occurrence of dysgeusia, burning mouth sensation, halitosis and reduced taste sensation in non-SS sicca patients and patients with pSS. Although non-SS sicca patients do not fulfill Sjögren's syndrome classification criteria, they had similar or even worse oral complaints than the patients with pSS.[42] On the whole, having a second comparison group with patients suffering from dry mouth syndrome that was not secondary to an autoimmune disease (diabetes, menopause, hypothyroidism, radiotherapy, age, etc.) would be most valuable in determining whether the differences are due to an autoimmune process or the damage caused by dry mouth syndrome. The weakness of our study is that we did not have this second comparison group. In our future research a group of non-SS sicca patients will be included in order to gain a better insight into the association between some other autoimmune diseases, chemosensory dysfunction and oral disorders. A potential limitation of our study is our sample size and the fact that we have not used chemosensory threshold for the ascertainment of smell function. We believe our control patients to be representative of the general population. We also regard the patients with pSS recruited in this study as representative subjects typical of SS population.

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