Oral submucous fibrosis; Journey towards Malignancy

INTRODUCTION

Smoking, chewing of tobacco and areca nut (AN), consumption of alcohol has become common social habits in the world. Such habits may cause many oral potentially malignant disorders in people. World health organization (WHO) has divided oral potentially malignant disorders into two types:¹ a) Precancerous lesion: a morphologically altered tissue in which cancer is more likely to develop than its normal counterpart. B) Precancerous condition: a generalized pathological state or condition associated with significant increased risk of cancer.

Oral submucous fibrosis (OSMF) is one of the commonest precancerous conditions of oral cavity² that predominantly affects the people of South –East Asian origin.³ It is a collagen related disorder characterized by excessive abnormal collagen deposition in the oral submucosa leading to tissue fibrosis, hyalinisation and degenerative changes in muscles.⁴ The unique feature of this condition is its widespread involvement in any part of mouth that can result in scaring of tissues, dysphagia and trismus.¹ For the last few years, Prevalence of OSMF has increased even in young school going children⁵ and due to its malignant potential, it is considered to be a deliberated condition leading to many complications. It is very essential to diagnose this disease at an early stage to prevent further adverse effects on oral health.

What is OSMF?

The term OSMF is derived from three words; oral means mouth, submucosal means below the mucosa, and fibrosis means hardening and scarring.⁶ Pindborg and Sirsat in 1966 defined OSMF as, “an insidious chronic disease affecting any part of the oral cavity and sometimes the pharynx. Although occasionally preceded by and/ or associated with vesicle formation, it is always associated with a juxta- epithelial inflammatory reaction followed by a fibroelastic change of the lamina propria, with epithelial atrophy leading to stiffness of the oral mucosa causing trismus and inability to eat.”⁷ WHO in 1978 defined OSMF as, “a slowly progressive disease in which fibrous bands form in the oral mucosa, ultimately leading to the severe restriction of movement of the mouth including tongue.⁸

Historical Background

OSMF is well established in Indian medical literature since the time of Sushruta, a surgical genius of the ancient India who described a condition termed “Vidari” as “progressive narrowing of mouth, de pigmentation of oral mucosa and pain on taking food”.⁹ Schwartz in 1952 described this disease in five Indian women settled in Kenya with a condition of the oral mucosa including palate and the pillars of the fauces, which he called it “atrophica idiopathica mucosae oris.¹⁰ Later on many terminologies have been used for OSMF like, ‘Submucous fibrosis’¹¹ ‘Diffuse oral submucous fibrosis,¹² ‘Idiopathica scleroderma of the mouth’,¹² ‘Idiopathic palatal fibrosis’,¹² ‘Sclerosing stomatitis¹² ‘Juxta epithelial fibrosis¹² and ‘Asian sideropenic dysphagia’¹³.

Epidemiology (Table 1)

OSMF occurs predominantly among Indians and people of Indian origin living outside India.¹⁴ Worldwide, estimates indicate that 2.5 million people are affected by this disease.¹⁵ Total number of cases in India is around two million and other countries involved are Kenya, Malaysia, Uganda, South Africa, and the UK.¹⁶ The disease is commonly seen in young to middle age group, however it can occur at any age.^17-20 For the recent years, school going children are also getting affected by this disease due to addiction of areca nut; the main causative agent.²¹ Even it can also affect paediatric age group.²² There is female predilection of this disease, that can be correlated to the nutritional deficiency particularly iron, in the Indian females.²³ However, some studies reveal the male predominance.^24-26

Aetiology

OSMF is a disease of multifactorial etiology. Main causative agent is Areca nut (AN) either in raw or baked form.²⁷ Major constituents of the AN are carbohydrates, fats, proteins, crude fiber, polyphenols, alkaloids and mineral matter.²⁸ Two major polyphenols are flavonoids and tannins that constitute a large proportion of the dry weight of the nut. It contains at least 9 structurally related pyridine alkaloids out of which four (arecoline, arecaidine, guvacine and guvacoline) have been conclusively identified.²⁹ Copper (Cu) represents the most abundant mineral in AN.³⁰ Average daily intake of Cu gets increased from 1.6 mg/day in a normal adult up to 5 mg/day in a daily AN chewer.³¹

Other contributory factors for OSMF include; Tobacco, chilies, nutritional factors, genetics, autoimmunity and infections.^32-50 (Table 1)

In few of studies it was observed that OSMF has developed even in the individuals without any habit of AN. This led to an indication of some other aetiopathological factors associated with OSMF. Recently, fibrinogen degradation products (FDPs) have been identified in the plasma of OSMF patients which has provided a new direction for etiopathogenesis of this disease.⁵¹ FDPs, also termed as Fibrin split products are components of blood, produced by clot degeneration. It has been found that fibrin precipitating factor (FPF) is present in the saliva of OSMF patients and behaves like thrombin. When this FPF encounters fibrinous exudates in the oral cavity, it clots the exudates, and the body in response to this clotting produces more fibrinogen and its degradation products.⁵²

Hence, as the severity of disease increases, more amount of FPF is produced and in turn more amount of FDPs is noticed. Increased level of plasma FDPs is a valuable early diagnostic sign of OSMF and these products have been found even in plasma of cancer patients suggesting their role in increasing the severity of premalignant and malignant disorders.^53-57 But still large-scale studies are needed to evaluate their exact role in the etiopathogenesis of these high-risk lesions.

Pathogenesis (Fig.1 & 2)

OSMF is considered to be a collagen related disorder characterized by excessive abnormal collagen deposition in the oral mucosa below the connective leading to tissue fibrosis, hyalinization and degenerative changes in muscles.4 The process is regulated by cytokines and growth factors and the expression of these mediators and their corresponding receptors. Central to the pathogenesis of OSMF is fibrosis, which could be either because of increased proliferation of fibroblasts and/or increased synthesis of collagen fibrils and decreased collagen degradation. 

AN being the main causative agent for OSMF, plays a crucial role in this pathological process. Arecoline; the major alkaloid of AN, stimulates fibroblasts to increase production of collagen.⁵⁸ Studies have shown that arecoline is an inhibitor of metalloproteinases (particularly metalloproteinase-2) and a stimulator of tissue inhibitor of metalloproteinases, thus decreasing the overall breakdown of tissue collagen.⁴² Flavonoid, catechin, and tannin helps in cross linking of collagen fibre making them less susceptible to collagenase degradation. Cu helps in stimulating fibrogenesis through up-regulation of Cudependent lysyl oxidase activity.⁵⁹

The alkaloids and flavonoids, from the AN are absorbed and undergo metabolism. Alkaloids mainly arecoline undergoes nitridation and gives rise to N nitrosamines, which might have a highly cytotoxic and genotoxic effect on cultured human oral mucosal epithelial cells and fibroblasts.⁶⁰ In addition, constituents of AN and their metabolites act as a source of constant irritation to oral tissues, thus the microtrauma produced by the friction of AN fragments also facilitates the diffusion of alkaloids and flavonoids into the subepithelial connective tissue, resulting in juxta epithelial inflammatory cell infiltration.⁶¹ Over a period of time, due to persistent habit, chronic inflammation sets in at the site and it is characterized by the presence of activated T cells, macrophages which produces various chemical mediators of inflammation, especially prostaglandins (PGs).⁴⁶

Cytokines like interleukin-6, tumor necrosis factor (TNF) and interferon ά along with growth factors like transforming growth factor β (TGF-β).^62,63. TGF-β is a key regulator of extra cellular matrix (ECM) assembly and remodeling. Two main pathways regulated by TGF-β are collagen production pathway and collagen degradation pathway, along with the chemical constituents present in areca nut which finally result in extensive tissue fibrosis.⁴⁶

Collagen production pathway is regulated by TGFβ that activates the procollagen genes, resulting in production of more pro-collagen. It also induces the secretion of procollagen C-proteinase (PCP) and procollagen N-proteinase (PNP), both of which are required for the conversion of procollagen to collagen fibrils. In OSMF, there is increased crosslinking of the collagen, resulting in increased insoluble form. This is facilitated by increased activity and production of a key enzyme – lysyl oxidase (LOX). The LOX is dependent on copper for its functional activity. During the biosynthesis of LOX, copper is incorporated into LOX.⁶⁴ During the process of cross-linking, Cu plays an important role in deoxidizing the reduced enzyme facilitating the completion of the catalytic cycle.

Collagen Degradation

Pathway is also regulated by TGF- β. TGF-β activates the genes for tissue inhibitor of matrix Metalloproteinase (TIMP); thereby more TIMP is formed. This inhibits the activated collagenase enzyme that is necessary for the degradation of collagen. It also activates the gene for plasminogen activator inhibitor (PAI), which is an inhibitor of plasminogen activator, thus plasmin formation is significantly reduced. Plasmin is required for the conversion of pro collagenase to active form of collagenase. The flavonoids of areca nut also inhibit the collagenase activity. A reduction in the activity and levels of collagenase results in a decrease in collagen degradation.⁴² Overall effect of both the pathways is OSMF.

Clinical signs and symptoms (Table 3)

The onset of disease is 2-5 years. The symptoms vary according to the stage of disease. (Fig. 3) Various classifications have been given for the clinical staging of OSMF. The disease is preceded by symptoms such as burning sensation of the oral mucosa, ulceration and pain.65 The characteristic features of OSMF are loss of pigmentation, leathery texture and blanching of oral mucosa giving rise to marble-like appearance, reduced movement of tongue, progressive reduction of mouth opening and sunken cheeks. In the more advanced stage, there is deposition of fibrous bands in the buccal mucosa and even other sites resulting in more trismus, shrunken uvula, speech and deglutition defects. The disease is proceeded further with the manifestations of premalignant and malignant changes in the oral mucosa.¹

Diagnosis

Clinical history, typical oral symptoms are sufficient to make clinical diagnosis of OSMF, however to evaluate the stage of progression, histopathological examination is essential. Many other investigations can be helpful to diagnose the specific features of this disease like use of immunohistochemical makers, AgNORs. In few studies, role of saliva has also been described as a diagnostic tool of OSMF.

Histopathology

Histopathologically OSMF is characterized by marked epithelial atrophy, loss of rete pegs and subepithelial hyalinization with abundant fibrosis and muscle degeneration. (Fig. 4)

Hyalinization is the result of excessive cross linking of collagen fibers due to components of AN. Epithelium may show dysplastic features. [1] Dysplastic changes are significant of high-risk malignant transformation potential of OSMF. Pindborg JJ and Sirsat SM (1966) [65] grouped OSMF into 4 stages histopathologically. Changes occur depending on the stage of disease. (table 4)

Laboratory investigations:

Haematological:

OSMF patients manifest with various haematological abnormalities such as decreased Hb, T- Lymphocytes count, serum Fe, calcium, protein (mainly albumin) , beta carotene, vitamin B complex, Zn, Cu, Serum antioxidants levels, LDH IV/II ratio; and there is increased ESR, tissue iron binding capacity, IgG, IgA, IgM, Eosinophil count, serum mucoproteins, Cadmium, Selenium, Magnesium levels.²³ Recently it has been found that plasma FDPs are also increased in the patients of OSMF, their levels increases according to progression of clinical grade of OSMF.^53-57

Immunohistochemistry:

Since immunodysregulation has been observed in OSMF patients, so various immunohistological markers can be used to diagnose the disease. Many Studies revealed that all cases of OSMF showed CD3 +ve, CD4 +ve cells in the basal layer of epithelium, juxta - epithelium and lamina propria when stained with HLA-DR antibody. Only few cells were CD8 +Ve and CD45RA +ve. There was increased expression of vimentin⁶⁶, Plasminogen activator inhibitor -1⁶⁷, keratinocyte growth factor -1⁶⁸, cystatin C⁶⁹ in buccal mucosa fibroblasts of OSMF patients, altered expression of p53, bcl2, bax and ki-67 markers. Mutations in Tumor suppressor gene adenomatous polyposis coli have been found that could also be potentially involved in the malignant potential of OSMF.⁴³

AgNORs:

Silver binding nucleolar organizer region proteins (AgNOR) act as a simple and reproducible cytological test indicative of proliferative status of cells, particularly of hemopoietic and epithelial origin.¹ Some studies reveal progressive increase in mean AgNOR count in OSMF cases as compared to normal mucosa.⁷⁰ Counting of AgNOR may be useful as a predictor of the biological behaviour of OSMF.

Saliva as a biomarker:

In some studies, it has been found that saliva of OSMF patients has shown a higher level of S-100A7, Salivary 8-hydroxy-2-deoxyguanosine (8-OHdG), monoaldehyde (MDA), LDH, total salivary protein and lipid peroxides as compared to normal individuals and decreased levels of salivary superoxide dismutase (SOD), vitamins A, C and E.⁷¹ Thus, oxidative stress is correlated with progression of disease. S100 proteins are a small, acidic, multigene, calcium-binding family containing approximately 25 members, each coded by a separate gene. High S100A7 expression is observed in potentially malignant oral disorders and is associated with the risk of malignant transformation in oral dysplasia. Its presence in saliva of OSMF patients indicates the risk potential of this disease.⁷²

Complications:

OSMF may lead to many other complications such as malnutrition, speech defects, airway problems, masticatory difficulty, deafness and risk of malignancy.⁷³

Malignant potential and precancerous nature of OMSF

OSMF is classified as an oral potentially malignant disorder (OPMD). Patients with OSMF have been reported with higher risk of developing oral squamous cell carcinoma (OSCC), compared to other diseases.⁷⁴ In a 17-year follow up study reported in 1970, it was found that 7.6% of OSMF cases got transformed to OSCC75, Which was increased up to 9% in later studies.^75,77 It has been found that Areca products and their derivatives such as arecoline- and nitrosamines have the ability to induce neoplastic changes in the oral mucosa.⁷⁸ Dense fibrosis and less vascularity of the corium, in the presence of an altered cytokine activity creates a unique environment for carcinogens from both tobacco and AN to act on the epithelium. Carcinogens from AN accumulate over a long period of time either on or immediately below the epithelium allowing the carcinogens to act for a longer duration before it diffuses into deeper tissues. (Fig. 1)

Differential diagnosis

Features of OSMF resemble to many other conditions either clinically or histologically, making the diagnosis difficult many times. So, it is important to know the characteristic findings which could make the differentiation clear. Differential diagnosis for OSMF include:

• Oral manifestations of scleroderma (symptoms are seen on skin also and there is widened periodontal ligament space)^79,80

• Oral lichen planus (Wickham striae may mimic fibrotic bands)⁸¹

• Fe deficiency anaemia (pale oral mucosa may mimic atrophic fibrosis)⁸²

• Amyloidosis (hyalinized stroma may mimic OSMF, but Congo- red & Thioflavin–T can be used)⁸³

• Generalized fibromatosis⁸⁴

• Radiation fibrosis, TMJ ankylosis, Actinomycosis which can lead to trismus as seen in OSMF⁸⁵

Management (Table 4)

Conventional therapies used in the management of OSMF are empirical and symptomatic. First most focus is to diagnose the etiological factor responsible for the disease. History regarding habit, psychological status and stress should be evaluated. Detailed medical and family history to rule out any genetic involvement is also necessary. Patient must be encouraged about the discontinuation of AN chewing habit. Other measures are use of nutritional support, Immunomodulatory drugs, local drug delivery, combined drug therapy, physiotherapy, hyperbaric oxygen therapy, natural compounds use, stem cell therapy and in severe cases surgical approach.^86-99 Ayurvedic treatment has also been implicated in OSMF patients and has shown effective results in various studies. Surgery is usually not recommended to treat OSMF, as it leads to more disability and fibrosis, but few techniques have been used. Autologous bone marrow stem cell injections induce angiogenesis in the area of lesion which in turn decreases the extent of fibrosis thereby leading to significant increase in mouth opening.¹⁰⁰

Summary

OSMF is one of the commonest premalignant condition of oral cavity having multifactorial etiology, but areca nut being the major cause. It widely involves the oral cavity leading to changes in oral environment making it more prone to get transformed into squamous cell carcinoma. Due to increasing addiction of areca nut even in school going young children, risk of developing OSMF has enhanced for the last few years. It has become a challenging task to diagnose because of its close resemblance to many other dermatological disorders like scleroderma. A thorough understanding of its etiopathogenesis, clinical features, early diagnosis and management has become important now a days for a general practitioner as well as dentist. Large scale studies are still required to rule out the exact pathogenesis of this disease to prevent further progression of symptoms.