Structural and functional abnormalities of the tongue: An epidemiological study from a tertiary care center in India

Background The tongue is a prominent muscular organ of the oral cavity and the integrity of the tongue mucosa frequently can reflect the overall health of an individual. Many notable structural and functional alterations can affect the tongue. These changes may be symptomatic or asymptomatic. Hence, the aim of the study was to determine the prevalence of structural and functional abnormalities of the tongue in a population reporting to a tertiary care center. We also assessed the prevalence of the normal variants and evaluated the normal tongue protrusion measurement in the study population. Methods The cross-sectional study included 1,143 dental outpatients above 18 years of age who visited the Department of Oral Medicine and Radiology between October 2021 to February 2022. Demographic details of the patients were noted. Participants were asked questions regarding any symptoms or abnormalities noticed on the tongue. The tongue was examined thoroughly for any structural/ functional abnormalities. The maximal tongue protrusion for each participant was measured by asking them to extend their tongue out. Medical history, drug history, and social history were recorded. Results The study included 564 male and 579 female participants; tongue lesions were positive in 66.5% of the study population. Coated tongue (26.2%) was the most frequent structural abnormality that was noted in the present study. Taste dysfunction (4.6%) was the most frequent functional abnormality. The lesions were mostly in the anterior two-thirds (4.2%) of the tongue. Functional abnormalities of the tongue were noted in 8.7% of the study participants. Conclusions The results of the present study showed that structural and functional abnormalities of the tongue were present in 66.5% of the population. Careful and detailed evaluation of the tongue examination is mandated in routine dental checkups. This shall help in the prompt identification of various etiological factors causing structural and functional abnormalities of the tongue.


Background
The tongue is a prominent muscular organ of the oral cavity and the integrity of the tongue mucosa frequently can reflect the overall health of an individual.Many notable structural and functional alterations can affect the tongue.These changes may be symptomatic or asymptomatic.Hence, the aim of the study was to determine the prevalence of structural and functional abnormalities of the tongue in a population reporting to a tertiary care center.We also assessed the prevalence of the normal variants and evaluated the normal tongue protrusion measurement in the study population.

Methods
The cross-sectional study included 1,143 dental outpatients above 18 years of age who visited the Department of Oral Medicine and Radiology between October 2021 to February 2022.Demographic details of the patients were noted.Participants were asked questions regarding any symptoms or abnormalities noticed on the tongue.The tongue was examined thoroughly for any structural/ functional abnormalities.The maximal tongue protrusion for each participant Any reports and responses or comments on the article can be found at the end of the article.

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was measured by asking them to extend their tongue out.Medical history, drug history, and social history were recorded.

Results
The study included 564 male and 579 female participants; tongue lesions were positive in 66.5% of the study population.Coated tongue (26.2%) was the most frequent structural abnormality that was noted in the present study.Taste dysfunction (4.6%) was the most frequent functional abnormality.The lesions were mostly in the anterior twothirds (4.2%) of the tongue.Functional abnormalities of the tongue were noted in 8.7% of the study participants.

Conclusions
The results of the present study showed that structural and functional abnormalities of the tongue were present in 66.5% of the population.
Careful and detailed evaluation of the tongue examination is mandated in routine dental checkups.This shall help in the prompt identification of various etiological factors causing structural and functional abnormalities of the tongue.

Introduction
The tongue is a prominent muscular organ of the oral cavity that plays a vital role in speech, mastication, and digestion.The integrity of the tongue mucosa frequently reflects the oral and systemic health of an individual. 1 The oral cavity, being the portal of entry to various infectious and carcinogenic agents, mucosa of the tongue is easily exposed to pathologic changes. 2 Numerous oral and systemic diseases affect the tongue, impairing its structure and function, and owing to its strategic position, those tongue changes can be easily appreciated.Notable structural alterations including the color, texture, size, shape, and appearance of the tongue can occur due to a variety of local causes or systemic conditions.Functional abnormalities of the tongue include inability/restriction of the tongue movements, taste disturbances, and/or discomfort.This can often occur in neurological conditions (palsy), oral submucous fibrosis, malignancy affecting the base of the tongue, neuromuscular disorders, and post-radiotherapy.The tongue changes can either be due to local factors like trauma, contact allergy, benign, reactive, or malignant growth or due to underlying systemic conditions like anemia nutritional deficiencies, infections, hormonal disturbances, immune-mediated diseases, and metabolic conditions. 3Even though tongue manifestations can be the early and easily identifiable diagnostic clue, it is often overlooked during a dental examination unless the patients report specific tongue complaints.Various studies have assessed the prevalence of tongue abnormalities in different population groups, however, the clinical correlation with the changes noted in the tongue is seldom looked into. 1,35][6] However, we could not find population-specific studies that have assessed both the structural and functional abnormalities of the tongue.The present study intended to assess the prevalence of structural and functional abnormalities of the tongue in patients visiting a tertiary care hospital and its possible association with the patient's history and the symptoms reported.This study will help in the understanding of the commonly encountered symptomatic and asymptomatic tongue abnormalities in patients.The present study also assessed the physiological range of tongue protrusion in the study population as such data is unavailable in the literature.The inclusion criteria were all patients above 18 years of age (Indian origin) who visited the dental and medical outpatient department.Patients with severe restriction in mouth opening, those who were not able to provide the consent for the study (patients with psychiatric disorders), or not willing to participate were excluded from the study.Informed written consent was obtained from individuals who were willing to participate in the study.The following data were noted down for each patient: age, and gender, and the participants were asked about any symptoms or abnormalities noticed on the tongue.Also, the medical history, drug history, and oral abusive habit history were recorded for each patient in a specially designed proforma.

Clinical examination
The clinical examination of the oral cavity and tongue was performed following WHO guidelines (Geneva, 1997) in a well-lit, noisy, and crowd-free room on a dental chair with artificial lighting and a mouth mirror under aseptic conditions. 7hree examiners independently (authors: AP, MK, RS) performed the clinical examination of the tongue for the patients and in case of doubt consensus was arrived after consultation with a clinical expert (authors RV -with over fifteen years of experience).Any structural abnormality of the tongue related to color, texture, size, shape, or appearance were noted.The tongue was checked for depapillation, coating or inflammation, any ulcers, white lesions, red patches, pigmentation, varices, and growth/swelling.

REVISED Amendments from Version 1
The title was modified as per the suggestions of the reviewer.The first author affiliation has been changed.The abstract has been made complete with all the relevant details of the study.The introduction has been rephrased.The relevant additional information regarding the inclusion and the exclusion criteria and the examiners have been incorporated.We have added two additional tables (Tables 2 & 3 in the revised manuscript) depicting the site-wise distribution of structural tongue abnormalities in both the genders and various age groups (18-40, 41-65, >65 years of age) in the study population.The flow of the information in the results have been modified as per the suggestions in the revised manuscript.The conclusion has been revised for clarity in the revised manuscript.
Any further responses from the reviewers can be found at the end of the article If any of the mentioned changes were observed, the location, extent, and surface characteristics of these lesions were recorded.The oral mucosal pathologies were clinically diagnosed based on their characteristic history and presenting features.The diagnosis of lichen planus was given when a bilateral white lacy pattern was observed with characteristic Wickham's striae.When scrapable white patches were seen in medically compromised patients leaving behind erythematous surfaces on rubbing a diagnosis of candidiasis was recorded.Leukoplakia is defined as "white plaques of questionable risk having excluded (other) known that carry no increased risk for cancer.It was diagnosed by excluding other causes of raised non-scrapable white diseases or disorders patches, especially in patients with a strong habit history.Erythroplakia appeared as a raised red velvety patch that could not be attributed to any other disease.Oral submucous fibrosis is typically diagnosed in the presence of fibrotic bands and the marbled appearance of the buccal mucosa.Erythema multiforme presents as multiple oral ulcers with crusting of the lips.Allergic stomatitis is established when multiple acute onset ulcers/erythema with a history of known triggering agents. 8Suspicious growth with induration of base is diagnosed as malignancy and was sent for histopathologic examination for definitive diagnosis.
Also, subjective symptoms and functional abnormalities like dysgeusia, burning tongue, taste loss, and tongue protrusion interferences were noted.Tongue movements were evaluated and maximal tongue protrusion was measured.This was performed by asking the patient to protrude the tongue to the maximum, and measurement was done using a sterile steel scale by measuring the distance between the maxillary incisal tip and the tip of the tongue (Figure 1).Any deviation of the tongue during protrusion or difficulty in protrusion was also recorded.

Data analysis
All the analysis was done using SPSS (RRID: SCR_002865) version 18 (SPSS Inc.Released 2009.PASW Statistics for Windows, Version 18.0.Chicago: SPSS Inc.).A p-value of <0.05 was considered statistically significant.Categorical variables were compared using Fisher's exact test or Chi-squared test.

Results
The study population included 1,143 patients of which 564 were male (49.3%) and 579 were female (50.7%).The mean age of the subjects was 38.59 years old with an age range of 18-85 years old (Standard Deviation; SD=13.88).Among the various comorbidities observed, 10.5% of the study population presented with diabetes mellitus followed by hypertension (8.9%), thyroid disorders (5.0%), immunocompromised state (2.8%) and anemia (0.8%).Oral abusive habits were reported by 25.7% of the subjects.Tobacco consumption (14.6%) was more commonly reported than alcohol (11.1%).Subjective symptoms including pain (7.0%) and burning sensation (8.2%) were also reported by the study population.Overall, 91.3% of them had a normal texture of the dorsal surface of the tongue and 7.1% had smooth bald tongue.The coral pink colored physiologic appearance was noted in 91.9%, 5.9% had a red tongue and 0.9% had a pale tongue.Figure 3 shows the topographic distribution of the tongue abnormalities observed in the study population.Figure 4 shows the various structural abnormalities observed in the present study.
The distribution of various structural tongue abnormalities is presented in Table 1. 15   The schematic representation of the common structural abnormalities of the tongue observed in the present study is shown in Figure 2.
When the site-wise distribution of structural tongue abnormalities were compared amongst the genders, males showed a statistically significant increase in the abnormalities in the anterior two-thirds of the tongue, the floor of the mouth, and the lateral border of the tongue (p=0.001,p<0.001, p<0.0001 respectively) (Table 2).
Also, subjects between 41 to 65 years of age showed statistically significant difference in the structural lesions occurring in the floor of the mouth and the lateral border of the tongue (p<0.001 and p=0.024 respectively) compared to the other age groups (Table 3).
Functional abnormalities of tongue were noted in 8.7% of the study participants of which 3.7% had restricted tongue movement (Table 4).
The range of tongue protrusion observed in the study was 15 mm to 54 mm with a mean of 40.5 mm.Table 5 depicts the range of tongue protrusion in the study population.
Using Fischer's exact test, the association between tongue abnormalities and tobacco-associated habits was assessed.
There was a positive association of tobacco-related habits with burning, pain, oral submucous fibrosis, verrucous carcinoma, squamous cell carcinoma, coated tongue, candidiasis, restricted tongue movement, and taste dysfunction (Table 6).

Discussion
Tongue abnormalities are commonly encountered in dental practice but often overlooked, if asymptomatic.The tongue may be affected by a wide range of local and systemic conditions.Structural and functional tongue abnormalities can be easily recognized on careful and detailed clinical examination.The present study evaluated the prevalence of structural and functional abnormalities of the tongue in a tertiary care hospital-based population.There is limited literature on the measurements of normal protrusive tongue movements.Understanding the physiologic range of tongue protrusion in a normal population aids in the early identification of tongue restriction.Restriction in the tongue protrusion occurs in various conditions like oral submucous fibrosis, carcinomas of the base of the tongue, scleroderma, and neurological disorders.
In the present study, overall tongue abnormalities were present in 66.5% of the subjects.A Turkish study by Avcu et al.  (2003) showed a prevalence of tongue lesions in 52.2% of the study subjects. 9[12] The anatomic distribution of tongue lesions was majorly noted on the anterior two-thirds of the tongue (4.2%) and least seen in the ventral surface of the tongue (0.3%).A study on the Libyan population showed that 90% of the lesions were on the dorsum, followed by the lateral border (7%), and posterior one-third (2%).The least common site was the ventral surface of the tongue (1%), which is in accordance with the present study.The most prevalent comorbidity in the study population was diabetes mellitus (10.5%), followed by hypertension (8.9%).Bhattacharya et al. (2016) estimated the prevalence of diabetes mellitus to be 3.1%, which is lower than the observations from the current study. 3A similar study on the Libyan population by Byahatti et al. (2010) found an even lower prevalence of subjects affected with diabetes mellitus (0.4%), followed by hypertension (0.3%). 12 Patil et al. (2013) conducted a study in which the prevalence of anemia was 3.8%, which was higher in comparison to the present study. 13 the present study, 5.9% had a red erythematous tongue and 0.9% had a pale tongue.Physiologic melanin pigmentation of the tongue was noted in 4.8% of the study subjects, whereas other studies by Mumcu et al. (2005) 14 and Shinde et al.
(2017) 11 were 6.9% and 2.1%, respectively.There is no literature available that has assessed the prevalence of other color variations on the tongue.
A positive oral abusive habit history was noted in 25.7% of the study population, of which 14.6% were tobacco users and 11.1% had alcohol consumption.In a study done by Motallebnejab et al. (2008), 54.7% of patients smoked tobacco and 35.3% had an alcohol habit. 15Other studies had estimated the prevalence of tongue lesions in smokers to be 1.93%. 12 positive association between smoking and the presence of hairy tongue was found by Darwazeh et al. (2010). 16ere was a positive association between tobacco-related habits and a burning sensation of the tongue in the present study.Tobacco-related habits were also associated with coated tongue, ulcers, increased incidence of candidiasis, oral lichen planus, oral submucous fibrosis, verrucous carcinoma, squamous cell carcinoma, restricted tongue movement, and taste dysfunction.Similarly, Bhattacharya et al. found a positive association between oral lichen planus and oral abusive habits. 3Avcu et al. estimated the correlation between tongue lesions and smoking in the Turkish population and concluded that tongue lesions (hairy tongue, fissured tongue, and coated tongue) were increased in smokers and heavy smokers than in non-smokers. 9Among the structural tongue abnormalities, the coated tongue was the most prevalent finding (26.2%), followed by depapillation (6.3%), ulcers (4.2%), enlarged tongue (3.1%), oral submucous fibrosis (2.5%) in the present study.Similarly, the coated tongue was the most prevalent finding (30.6%) followed by a fissured tongue (20.1%) 3 in a study conducted by Bhattacharya et al., on the Indian population.The prevalence of coated tongue was 28.0% in an Indian study 13 by Patil S et al.Shinde et al. (2017) estimated the prevalence of fissured tongue (51.7%) was high, followed by coated tongue (14.3%), and geographic tongue (10%). 11A higher prevalence of fissured tongue (48.4%) was observed in a study in the Libyan population. 12By contrast, a very low prevalence of 1.1% with fissured tongue was noted in our study population.Lingual varicosity was noted in 8.5% of our subjects.Whereas, varicosity was the least common finding (0.4%) in an Indian population by Bhattacharya PT. 3 To the best of our knowledge, the present study was the first to evaluate the presence of functional abnormalities of the tongue that included restriction of tongue protrusion and taste dysfunction.No literature has addressed the various functional abnormalities that affect the tongue in a large population.Taste abnormalities were reported in 4.6% of the study population; 6.5% of the study subjects had tongue protrusion less than 30 mm.This is the first study that has evaluated the functional as well as structural abnormalities affecting the tongue.Kotlow et al. (1999) graded ankyloglossia into four classes: Class I-Mild (12-16 mm), Class II-Moderate (8-11 mm), Class III-Severe (3-7 mm), Class IV-Complete (less than 3 mm). 17Considering the tongue protrusion range observed in the present study population and the classification of ankyloglossia, we propose a new grading for tongue protrusion, as depicted in Table 7.
Limitations of the present study include the observational nature due to which the contributing factors like oral hygiene, oral abusive habits, medications, and systemic disorders could not be associated with the findings on the tongue.Multicentric studies from diverse populations shall aid in a deeper understanding of the abnormalities that can affect the tongue.

Conclusion
The results from the present study reflected a high prevalence of structural and functional abnormalities affecting the tongue.These abnormalities may be either clinically symptomatic or incidental findings on routine oral examination.A careful and detailed evaluation of the tongue examination is mandated to rule out any significant oral lesions.This shall help in the prompt identification of various etiological factors causing structural and functional abnormalities of the tongue.Understanding the normal tongue protrusion range will aid in the early detection of restricted tongue movements.

General Comments
This manuscript was meant to report on the incidence and pattern of structural and functional abnormalities of the tongue.

Overall Assessment of the Manuscript
First and foremost the authors are congratulated for coming up with such an interesting study.
The authors have collected valuable data.There are some flaws in the manuscript as described in section wise comments.

Section-wise comments
The Title: The title length is acceptable.1.
The title is specific and concise.2.

Abstract:
It is according to the standards of the journal.1.
The aim of the article has been stated.2.
In the methods section, the authors summarize the necessary details.

3.
The main result has been described.4.
Conclusion: is out of the context, the aim is to report on structural and functional abnormalities, and not merely lesions of the tongue 5.

Keywords:
The number of Keywords is acceptable.1.
Keywords are not appropriate.

2.
Recommendation: Please re-write the keywords.

Introduction:
The introduction fails to describe the subject at hand adequately, it derails the reader from the main purpose of the study 1.
The rationale for carrying out this study is stated.2.
The objective is not apparent 3.
A few grammatical errors were noted.

4.
The knowledge gap that the authors are trying to address is apparent.

5.
A clear flow of thoughts between paragraphs and in some places between sentences within the same text is lacking.The authors have repeated some words and ideas within the same paragraph.
Recommendation: Please re-phrase the introduction.In the introduction section, the authors may add some literature review regarding the subject at hand.

Methods:
The study design is clearly described.1.
The population studied is not known.Though the authors report that the study was carried out in Manipal, it can not be assumed that the individuals recruited were Indians.

2.
Inclusion and exclusion criteria are very narrow.E.g Did the authors include patients with mental challenges, or those presenting with orofacial space infections?

3.
How many clinicians examined all the patients?4.
How were inter-and intra-observer reliability taken care of? 5.
The statistical analysis carried out has been briefly described 6.
Few grammatical errors were noted.7.

Results:
The results have been presented fairly and in a very simplified manned 1.

2.
The English used in the article is acceptable.1.
There are a few obvious grammatical mistakes.2.

Logic:
The article has been written clearly except for the introduction part. 1.
There is a minimum violation of grammar in the manuscript, however, it does not hinder the reader from grabbing information easily.

2.
Recommendation: There is room for improvements.

Are sufficient details of methods and analysis provided to allow replication by others? No
If applicable, is the statistical analysis and its interpretation appropriate?Yes Are all the source data underlying the results available to ensure full reproducibility?Yes

Are the conclusions drawn adequately supported by the results? Partly
Competing Interests: No competing interests were disclosed.
Reviewer Expertise: oral and maxillofacial surgery, oral medicine, head and neck oncology, clinical dentistry, oral and maxillofacial radiology I confirm that I have read this submission and believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard, however I have significant reservations, as outlined above.
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Figure 2 .
Figure 2. Schematic diagram depicting the distribution of the common structural abnormalities of the tongue.

Figure 3 .
Figure 3. Schematic diagram depicting the topographic distribution of the tongue abnormalities in the study population.

Figure 4 .
Figure 4. Various structural abnormalities observed in the present study.

Table 1 .
Frequency distribution of various tongue lesions.

Table 2 .
Table depicting the structural tongue abnormalities in various sites according to gender.

Table 3 .
Table depicting the structural tongue abnormalities in various sites according to the age range of the study population.

Table 4 .
Table depicting the frequency distribution of functional abnormalities of the tongue.

Table 5 .
Range of tongue protrusion observed in the study population.

Table 6 .
Association of smoking habit and lesions affecting the tongue. 12

Table 7 .
Proposed grading system of tongue protrusion inferred from the present study.