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CLINICO-PATHOLOGIC REVIEW OF BIOPSIED TONGUE LESIONS IN A NIGERIAN TERTIARY HOSPITAL.

Background: Varying pathologic conditions can affect the tongue for which the pattern of occurrence may differ. The aim of this study was to review the clinico-pathologic features of histologically diagnosed cases of tongue lesions that presented in our hospital over a 21 years period. Materials and Methods: Data on habits, class of lesion, histological diagnosis, age, gender, and site distributions were analyzed using descriptive frequencies, ranges and means ± SD. Variables were compared using Chi square and ANOVA tests as appropriate. Sites of lesions were coded using the WHO ICD-O code on topography. Results: Tongue lesions were seen in 43 males and 31 females. There was a bimodal peak age of occurrence at 40-49 and 60-69 years of age. Smoking and alcohol intake habits were recorded in 8 cases only. Neoplastic lesions constituted 78.4% of the cases. Using the WHO ICD-O code for topography of lesions, the tongue dorsum (ICD-O-2.0) was the most commonly affected site. Malignant lesions constituted 47.3% of the cases seen. Also, 8.6% of the malignant lesions were seen in younger patients (< 40 years). Conclusion: Tongue lesions showed a bimodal age of occurrence with neoplastic lesions as the most histologically diagnosed lesions in our study.


INTRODUCTION
The tongue is an important muscular structure in the oral cavity involved in the critical functions of taste, speaking, chewing and swallowing. 1 The condition of the tongue has been considered a good reflection of many systemic diseases 2,3 .However, varying pathologic conditions may affect the tongue of which chronic lesions often necessitate biopsy and histological diagnosis. 4 Most studies that reviewed tongue lesions were based on clinical assessment only. However, the pattern of occurrence of histologically diagnosed tongue lesions may vary across the globe. Generally, few studies [5][6][7] have reported clinico-pathologic review of histologically diagnosed tongue lesions which are mostly case specific. More importantly, none of these studies were from our environment. Thus, the aim of this study was to review the clinic-pathologic features of histologically diagnosed cases of tongue lesions that was presented in our hospital within the last 21 years  and also provide a reference data base from the region.

MATERIALS AND METHODS
This is a retrospective cross-sectional study of cases of tongue lesions seen between January 1995 and December 2015. Biopsy records of all histologically diagnosed cases seen in the Oral Pathology department of the University College Hospital Ibadan, Nigeria within the period were retrieved and included. Data on habit, class of the lesion, histological diagnosis, age, gender and site of lesions were analyzed descriptively using frequencies, ranges and means ± SD. Variables were compared using Chi square and ANOVA tests as appropriate. Patients were also grouped into either young (<40 years) or old (>40 years) age groups based on previous report of different clinicopathologic behavior of tongue lesions in the two age groups. 8,9 Sites of lesions were coded using the WHO ICD-O code on topography.

RESULTS
A total of 1807 biopsy cases were diagnosed during the period of which 74 cases (4%) were tongue lesions. The histological diagnoses of the lesions are shown in Table 1. The lesions were seen in 43 males and 31 females with a male to female ratio of 1.4:1. The mean age of occurrence was 46.41 ± 21.13 years (range = 1 to 92 years). The distribution of the lesions based on age group is shown in figure 1. There was a bimodal peak age of occurrence at 40-49 and 60-69 years. Gender distribution of the various classes of tongue lesions are shown in Table 2.
History of both smoking and alcohol intake was positive in only 8 cases (10.8%) out of which 7 cases (87.5%) were squamous cell carcinoma. In addition, habit of alcohol intake only was recorded in 3 cases      Neoplastic lesions constituted 78.4% with bimodal peak of age group of occurrence (40 to 49 years and 60 to 69 years while non-neoplastic lesions constituted 21.6% with peak of occurrence in the age group 10 to 19 years. Forty-one cases (70.8%) out of the neoplastic lesions were seen in the older age group (> 40 years), while 17 cases (29.2%) were seen in younger age patients (< 40 years). Out of the neoplastic lesions, malignant lesions constituted 60.3% of the cases seen with peak age group of occurrence of 60 to 69 years, while benign lesions constituted 39.7% with a peak

DISCUSSION
In this study, tongue lesions constituted an appreciable percentage (4%) of all histologically diagnosed cases of oral pathologic conditions in our institution. Our finding is almost similar to a recent report in a retrospective analysis of oral biopsies in Iran that documented 3.7% cases of tongue lesions. 10 However, our finding is contrary to the previous reports by Alaeddini et al. 11 , which indicated that tongue lesions constituted 6.3% of all the histo-pathologic cases seen at their center. The lower percentage from our results may be due the study population and the differences in the duration of the studies. The duration of our study was shorter when compared with that of Alaeddini et al. 11 Also, higher prevalence of oral lesions has been reported in their population, due to habits of tobacco use.
Neoplastic lesions were the most commonly diagnosed tongue lesions in this review. This finding may be explained by the design of the study which included only histologically diagnosed tongue lesions. While studies that reviewed tongue lesions based mostly on clinical presentations of patients reported higher prevalence of benign lesions, [12][13][14] those that involved histologically diagnosed cases, 11,15 reported higher prevalence of neoplastic lesions similar to our finding. However, contrary to our finding, a study that reviewed histologically diagnosed cases of tongue lesions from Brazilian population documented higher prevalence of non-neoplastic lesions. In their study, non-neoplastic lesions of the tongue constituted 53.5%. 16 The age groups mostly affected by tongue lesions with specific consideration to neoplastic tongue lesion were the 40 to 49 years and the 60 to 69 years age groups which are similar to previous studies. 11,16 According to Kantola et al. 17 , 91% of patients with tongue cancer were older than 40 years. However, the peak age group of non-neoplastic tongue lesions was 10 to 19 years.
These findings indicate that neoplastic tongue lesions affected older age groups whereas non-neoplastic tongue lesions affected younger age groups. Advancing age is the most significant risk factor for cancer overall, and for several discrete cancer types. According to a   recent statistical data from National Cancer Institute's Surveillance, Epidemiology, and End Results program, the median age of a cancer diagnosis is 66 years. It has been known for years that age is a leading risk factor for the development of many types of cancer, but why aging increases cancer risk remains unclear. A study suggested that the accumulation of age-related changes in a biochemical process involved in genes control may be responsible for some of the increased risk of cancer seen in older people. 18 It was proposed that DNA methylation, or the binding of chemical tags, called methyl groups, onto DNA, may be involved. Methyl groups activate or silence genes, by affecting interactions between DNA and the cell's protein-making machinery. It was reported that 70-90 percent of the sites associated with age showed significantly increased methylation in all cancer types studied. Thus age-related methylation may incapacitate the expression of certain genes, making it easier for cells to transform to cancer. 18 The anterior two-thirds of the tongue was the most commonly involved location for benign malignant lesions. The tongues' dorsum was the most commonly affected site. All the lesions that involved the base of the tongue were malignant neoplastic lesions. The percentage of lesions at the base of the tongue was much less than what obtained in some other regions. 19,20 This may be related to the fact that habits like placement of carcinogenic substances in the base of the tongue as well as the floor of the mouth which has been implicated in the etiology of oral cancer are not widely practiced in our environment. 21,22 Tobacco smoking and chewing, betel chewing and alcohol consumption are all more commonly consumed where tongue malignancies are highly prevalent. 23,24 Positive history of smoking and alcohol intake (the most implicated etiological factor in oral neoplastic lesions) was recorded in a very few cases of lesions studied. This finding is similar to a previous report 21 suggestive of other etiological causes of oral lesions in our environment. The differential diagnosis for lesions of the tongue vary from non-neoplastic to neoplastic and those involving the base of the tongue may include normal lymphatic tissue, ectopic thyroid tissue, lymphoma, lipoma, hemangioma, schwannoma, granular cell tumors, benign and malignant tumors of minor salivary gland origin, rhabdomyosarcoma, and metastatic disease.
Of the neoplastic tongue lesions reviewed, majority were histologically diagnosed as malignant lesions similar to previous reports. 11,16 Malignancies were commoner in the older age group compared with the younger age group in keeping with the trend worldwide. This age group had lesions in the base of the tongue, a trend completely not noticed in the younger age group in this study.
Tongue cancers constitute a significant proportion of oral cancers majority of which are SCC. [25][26][27] Studies in Nigeria have documented lower prevalence of tongue SCC compared to studies from non-Nigerian populations. Oji and Chukwuneke 28 and Effiom et al. 25 reported that tongue cancer constituted 30% and 17.4% respectively of all oral cancer cases seen in their studies Also, Lasisi et al. 22 reported 21 cases (13.5%) of tongue SCC of which 79.2% constituted well differentiated histological type. However, higher prevalence of tongue SCC has been reported in other populations. Hernandez-Guerrero et al. 29 , in an epidemiological study showed that the tongue is the predominant anatomic site for SCC (44.7%).

CONCLUSIONS
Findings from this review indicate that tongue lesions are relatively common in our environment with bimodal peak ages of occurrence, a predominance of neoplastic lesions and predilection for the dorsum and the anterior two-thirds of the tongue. Also all lesions presenting in the base of the tongue were malignant lesions with squamous cell carcinoma as the most common histological diagnosis.