Review Article Open Access
Journey of Leukoplakia So Far - An Insight on Shortcomings of Definitions and Classifications
Priyanka Kardam1*, Shweta Rehani1, Monica Mehendiratta2, Khushboo Sahay1, Yulia Mathias1 and Rashi Sharma1
1Department of Oral Pathology & Microbiology, Sudha Rustagi College of Dental Sciences and Research, Kheri More, Village Bhopani, Faridabad – 121002, Haryana, India
2Department of Oral Pathology & Microbiology, ITS Dental College, Greater Noida, Uttar Pradesh 201308, India
*Corresponding author: Dr. Priyanka Kardam, D-81, Ground Floor, Saket, New Delhi -110017India, Tel: 09717102171, E-mail: priyankakardam@gmail.com
Received: March 26, 2015; Accepted: May 20, 2015; Published: June 05, 2015
Citation: Kardam P, Rehani S, Mehendiratta M, Sahay K, Mathias Y, et al. (2015) Journey of Leukoplakia So Far – An Insight on Shortcomings of Definitions and Classifications. J Dent Oral DisordTher 3(2): 1-6.
Abstract
Leukoplakia is one of the most frequently encountered white lesions by the clinicians. The definitions and terminologies associated with leukoplakia have been proposed by various authors. Also, various attempts have been made to clinically and histopathologically grade leukoplakia by evaluating different criteria.

Although there are numerous reviews that have discussed the definitions and classifications of leukoplakia, none has attempted to provide a clear visualization of the shortcomings associated with each definition and classification. Hence, this review article is an attempt to highlight the main points as well as shortcomings in terminology, definitions, clinical classifications and histopathologic gradings which have been associated with leukoplakia till date.

Keywords: Leukoplakia; Dysplasia; Definitions; Classifications; Grading
Introduction
The term "leuko" refers to white and "plakia" signifies a plaque/patch. Hence, the literal meaning of the term leukoplakia is a "white plaque". More than any other oral disease, leukoplakia has suffered from an excess of diagnostic terms and definitions; at least 75 have been used thus far. This has led to such mystification that many clinicians refuse to use any term beyond "white patch" [1]. The first recorded white oral plaque/patch was an "ichthyosis" reported in 1818 by Alibert of Paris [2].

Although innumerous definitions and classifications have been devised, still there is a lack of consensus. The aim of this paper is to enlighten the highlights and shortcomings of these definitions and classifications. The knowledge and understanding of all the terminologies and classifications along with their shortcomings will provide a better insight for evaluating their appropriateness and comprehensiveness.
Terminologies and definitions
The first definitive terminology associated with leukoplakia was given by Schwimmer in 1877 [3]. Since then, numerous changes have been introduced by authors pertaining to size, etiology, exclusion of other lesions and potential for malignant transformation. The highlights, new points and shortcomings associated with each terminology have been consolidated in Table 1 [4-10].
Clinical classifications
Leukoplakia is one of the most commonly encountered white lesions by the clinicians and still holds an enigma around itself. Proper identification of the type of leukoplakia holds the key to successful treatment of the lesion. Hence, it is important for the clinician to recognize the type of leukoplakia as it can help in planning the treatment and also in predicting the malignant potential of the lesion [11].

Till date, numerous classifications for leukoplakia have been introduced based on criteria such as etiology, appearance, size and presence or absence of dysplastic features. Some authors have even commented, the clinical appearance of leukoplakia can be used to suspect the possibility of dysplasia being present in a lesion. Pindborg, et al. [12] confirmed that speckled leukoplakia was often associated with epithelial dysplasia or carcinoma as compared to homogenous leukoplakia. Sugar and Banoczy [13] in their three tiered clinical classification of 1969, reported that leukoplakia erosiva and leukoplakia verrucosa were more often associated with epithelial dysplasia than leukoplakia simplex. However, the clinical appearance cannot be confirmatively associated with presence or absence of dysplastic features. Various clinical classifications used for leukoplakia and their basis have been consolidated in Table 2 [14-17].
Histopathologic grading
Although leukoplakia is a pure clinical term and the lesion has no specific histology i.e. it may or may not demonstrate dysplasia. However for the purpose of histopathologic reporting, the term "dysplasia" has been used [18]. Various authors have proposed grading systems for leukoplakia, but each system has its own shortcomings. The highlights, new points and shortcomings of these grading systems have been consolidated in Table 3 [19-34].
Table 1: Terminologies and definitions associated with leukoplakia.

 

Author

 

Highlights

 

New Points

 

Shortcomings

Schwimmer [3]

(1877)

 

First used the term "Leukoplakia" to describe a white lesion

A specific terminology introduced for white lesions

Was very vague with no description regarding non-scrapability/ dissimilarity to other diseases

WHO sponsored meeting of investigators on Oral Precancerous conditions at Copenhagen [4] (1967)

A raised white patch of the oral mucosa measuring 5mm or more, which cannot be scraped off and which cannot be attributed to any other diagnosable disease

Size criterion introduced

No mention of etiologic factors

Pindborg [5] (1972)

A white patch or plaque on the mucous membrane that cannot be removed by rubbing and cannot be classified as any other diagnosable disease

 Removed the size criterion

No mention of etiologic factors

WHO collaborating centre for Oral Precancerous lesions [6]

(1978)

 

A white patch or plaque that cannot be characterized clinically or pathologically as any other disease

*Emphasized on absence of histological connotation

*Only terminology to emphasize on clinical exclusion of other white lesions

*Subjective as lesions like leukoedema created a problem

*Biopsy required to give diagnosis

*No emphasis on associated etiology

First International Conference on oral leukoplakia held at Malmo, Sweden.  Axell et al. [7]

(1984)

 

A white patch or plaque that cannot be characterized clinically or pathologically as any other disease and is not associated with any physical or chemical causative agent except use of tobacco

*Tobacco was clearly stated as the etiology

*Proposals for etiological and clinical description of leukoplakia

*Association with causative agents is difficult to assess

*Several tobacco induced lesions are partly white but are not traditionally described as leukoplakias

Bouquot JE [8] (1994)

A chronic white mucosal macule which cannot be scraped off, cannot be given another specific diagnostic name and does not typically disappear with removal of known etiologic factors

*Diagnostic definition

*First definition in which leukoplakia was mentioned as a precursor of malignancy

Known etiologic factors not mentioned

International symposium held in Uppsala, Sweden

(1994)  [9]

 

A predominantly white lesion of the oral mucosa that cannot be characterized as any other definable disease

Term "predominantly white" helped in excluding lesions like pre-leukoplakia and leukoedema which created an issue earlier

No description about the potential for malignant transformation

Axell T et al. [9]

(1996)

 

A predominantly white lesion of oral mucosa that cannot be characterized as any other definable lesion clinically or pathologically, often associated with tobacco products, some of which will transform into cancer

Emphasized that some oral leukoplakias will transform into cancer

 

Warnakulasuriya S et al. [10]

(2007)

 

A white plaque of questionable risk having excluded other known diseases or disorders that carry no increased risk of cancer

 

*Consideration should be given to reintroduce size and scrapability as a criterion

*It was very vague and nothing new was introduced

Table 2: Clinical classifications of leukoplakia.

 

Author

 

Based On

 

Clinical Types

 

Remarks

 

Mehta et al. [14]

(1971)

 

Clinical appearance

*Homogeneous – A raised plaque of variable size which is predominantly white but can be grayish or yellow

*Ulcerated – Red/yellowish area surrounded by white patches which appears like an ulcer

*Nodular – A white patch on an erythematous base

* It was the first attempt to clinically categorize leukoplakia

* It was clinically applicable

 

Pindborg et al. [5] (1972)

 

Clinical appearance

*Ebbing tide – Appears like indulations left on sand by an ebbing tide. Especially occurs on floor of the mouth

*Others– All other types of appearances were grouped together

*Inconclusive

*Not commonly used

 

Amagasa et al. [15] (1977)

Clinical appearance

*Type 1- Flat white patch/plaque without red components

*Type 2- Flat white patch/plaque with erosion or red components

*Type 3- Slightly raised or elevated white patch/plaque

*Type 4- Markedly raised or elevated white patch/plaque

Introduced the criteria of being flat or raised

 

Banoczy J [13]

 (1982)

 

Clinical appearance

*Leukoplakia Simplex - White homogeneous keratinized lesion, slightly elevated

*Leukoplakia verrucosa - White verrucous lesion with wrinkled surface

*Leukoplakia erosiva - White lesion with erythematous, erosion, fissures

For the first time verrucous lesions were mentioned separately

Axell et al. [9]

 (1984)

 

Etiology

*Idiopathic - Etiology unknown

*Tobacco associated leukoplakia – Caused by tobacco

It was difficult to apply clinically

 

International symposium held in Uppsala, Sweden [9]

(1994)

 

 

Clinical appearance

*Homogenous – Predominantly white with cracked/wrinkled/smooth surface but a consistent texture throughout.

*Non-homogenous Leukoplakia –

Erythroleukoplakias – Red and white lesion

Nodular – slightly raised, rounded, red and/or white excrescences

Exophytic – irregular blunt or sharp projections

 

Clubbed nodular and ulcerative together

 

Schepman [16]

 (1995)

 

 

Size (L), Site (S), Clinical aspect (C) and Histopathological features (P)

Provisional (Clinical) Diagnosis

1st symbol: L = Extent of leukoplakia

L0 = No evidence of lesion; L1= Lesion<2 cm; L2 = Lesion >2cm to 4 cm; L3 = Lesion >4 cm; Lx = Not specified

2nd symbol: S= Site of leukoplakia

S1 = All oral sites except for floor of mouth & tongue

(Low Risk Sites); S2 = Floor of mouth and / or the tongue (High Risk Sites); Sx = Not specified

3rd symbol: C = clinical Aspect

C1= Homogenous; C2= Non-homogenous;C3= Not specified

Definitive (Histopathological) diagnosis

4th symbol: P = Histopathological features

P1 = No dysplasia; P2 = Mild dysplasia; P3 = Moderate dysplasia; P4 = Severe dysplasia; Px = Not specified

Proposal for staging system for Oral leukoplakia

Stage I =   Any L, S1, C1, P1 or P2

Stage II =  Any L, S1, C2, P1 or P2

                  Any L, S2, C2, P1 or P2

Stage III = Any L, S2, C2, P1 or P2

Stage IV = Any L, any S, any C, P3 or P4

*It gave detailed description in terms of size, site and clinical aspect like TNM staging

* It was time consuming to use

 

Waal et al. [17]

    (2000)

 

Size & pathology of leukoplakia, focusing on absence or presence of epithelial dysplasia.

 

Symbol: L = Size of leukoplakia

L1 = Size of single or multiple leukoplakia together < 2 cm; L2 = Size of single or multiple leukoplakia together 2-4 cm; L3 = Size of single or multiple leukoplakia together >4 cm; LX = Size not specified.

Symbol: P = Pathology

P0= No epithelial dysplasia (includes no or perhaps mild epithelial dysplasia); P1= Distinct epithelial dysplasia (includes mild to moderate to possibly severe epithelial dysplasia.); PX= Absence of epithelial dysplasia is not specified in pathology report.

Staging system proposed was-

Stage I = L1P0

Stage II =L2P0

Stage III = L3P0 or L1L2P1

Stage IV = L3P1

* It was a simplified version of classification proposed by Schepman

* It was less time consuming as compared to classification given by Schepman

Table 3: Histopathologic grading systems associated with leukoplakia.

 

AUTHOR

 

HIGHLIGHTS

 

NEW POINTS

 

SHORTCOMINGS

 

Smith and Pindborg system [19] (1969)

*Attempted to standardize grading of dysplasia by photographic method

* 13 histological features were standardized by a set of photographs

*Each feature was graded as absent, slight or marked

*Dysplasia was graded as absent, mild, moderate and severe

 

Produces an assessment of dysplasia on an ordinal scale which facilitates statistical analysis

* Numerical scores for individual features have been allocated subjectively by the authors and are not evidence-based

*It suffers interobserver and intraobserver variability

* Time-consuming to use

Banoczy and Sciba [20]

(1976)

 

* Epithelial dysplasia was diagnosed using 9 dysplastic features suggested by Mehta et al (1971).

* Graded epithelial dysplasia as mild, moderate and severe

 

Dysplasia was graded on basis of number of dysplastic features.

Mild = 2 dysplastic features.

Moderate = 2 to 4

Severe = 5 or more

* Was based on subjective interpretation of the features

* Didn't take into account which factor was important in determining the malignant potential

W.H.O.[21]  (1978)

 

* Listed 12 histologic features that characterized

epithelial dysplasia

* Dysplasia was again graded as mild, moderate and severe

 

Grading was based on the thickness of epithelium involved, nuclear abnormalities, cell maturation and stratification and abnormal mitosis.

Following new dysplastic features were added:

1. Drop shaped rete ridges

2. Mitotic figures in superficial layers of epithelium

3. Enlarged nucleoli

 

* It suffers interobserver and intraobserver variability

* Didn't take into account which factor was important in determining the malignant potential

 

Kramer [22] (1980)

 

*Listed 14 dysplastic features

*Epithelium was called dysplastic if it showed presence of 2 or more of the dysplastic features

*Dysplasia was graded as present or absent

*Grading was based on the same criteria as that of WHO (1978)

*Following new dysplastic features were added:

1.Cell crowding

2.Abnormal mitosis

* It suffers interobserver and intraobserver variability

* Didn't take into account which factor was important in determining the malignant potential

 

 

Burkhardt and Maerkar [23-25] (1981)

Listed 6 histological and cytological parameters, based on which diagnosis and classification of epithelial dysplasia could be made. Dysplasia was graded as low, medium, high and Carcinoma in situ (CIS)

*A new category i.e. CIS was introduced

* Introduced additional indicators of dysplasia like increase  in  subepithelial lymphocytes,  plasma  cells  and interepithelial cells (stroma reaction) and presence of candida organisms.

 

 

 

 

Lumermann H. et al. [26] (1995)

 

 

Considered basal cell hyperplasia, nuclear enlargement and hyperchromaticity, drop shaped rete pegs as 'minimal' criteria for diagnosis of oral epithelial dysplasia.

Dysplasia was graded as mild, moderate, severe, CIS, Verrucous hyperplasia with dysplasia

*Grading was based on thickness of epithelium involved by minimal criteria of diagnosis

*A new category i.e Verrucous hyperplasia with dysplasia was introduced

* The new category (verrucous hyperplasia) creates confusion during grading

Neville et al. [27] (1995)

Graded dysplasia as mild, moderate, severe, CIS

 

 

 

Speight P M et al. [28] (1996)

 

 

Graded dysplasia as mild, moderate, severe

 

Considered the thickness (height) to which the cellular and tissue changes may extend, as important in grading dysplasia

Warnakulasuria (2001) commented that there was wide variation in the thickness of the covering epithelium in the oral cavity, with much undulation which lead to practical difficulties in using this grading system [29]

 

Kuffer and Lombardi [30] (2002)

*Proposed to dismember the classical "oral precancerous lesions" into following categories:

Risk lesions - which histologically do not show dysplasia (eg.  Simple tobacco keratosis)

Precursors of SCC-lesions with dysplasia (i.e. already engaged in the process of malignant transformation (eg; tobacco keratosis  with  dysplasia)

Introduced the terms risk lesions and precursors of SCC (squamous cell carcinoma)

*Using the term "risk lesion" for lesions without dysplasia which have a no risk of

Malignant transformation (eg. Frictional keratosis)

is inappropriate.

*All dysplasias do not progress to SCC, hence calling all dysplasias as precursors of SCC is not justified.

 

Brothwell D J et al. [31] (2003)

 

 

 

Graded epithelial dysplastic lesions according to 5 point scale;

0 = No dysplasia;1 = Mild;2 = Moderate;3 = Severe;4 = CIS

Using this system, and statistical analysis, authors proved that intra and interobserver agreement in grading the dysplastic lesions were consistent

 

Ljubljana [32] (2003)

*Developed to cater for the special clinical and histological problems of laryngeal abnormalities.

*Terms used were– Simple hyperplasia, abnormal hyperplasia, Atypical (risky) hyperplasia, CIS

 

 

Still doubtful if this system can be used satisfactorily for oral and oropharyngeal precursor lesions

 

 

WHO [33]

(2005)

 

 

*Grading was based on cytological and architectural dysplastic features listed by WHO in 2005.

*Dysplasia was graded as – Squamous hyperplasia, mild, moderate, severe dysplasia, CIS

 

Squamous hyperplasia introduced as a new category

 

Binary system [34] (2005) proposed by Omar Kujan et al.

* Considering the problems in making reliable distinctions between the different grades, 4 grades were collapsed to 2.

*Categories were: High risk lesions (with potential susceptibility  for  malignant transformation) and Low risk lesions  ( no potential  for malignant  transformation)

*With the reduction in number of grades, interobserver variability was expected to decrease

 

Conclusion
Leukoplakia has been one of the most debatable topics amongst the pathologists owing to its ever changing definitions, terminologies, classifications and interobserver and intraobserver variabilities. Till date, no definition, terminology, classification or grading has been declared to be ideal, and this leads to lack of uniformity in their usage by pathologists around the world. The knowledge and understanding of all the terminologies and classifications along with their shortcomings will provide a better insight for evaluating their appropriateness and comprehensiveness.
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