A Histomorphology Comparison of Saw-Tooth Shaped Rete Ridge Between Oral and Cutaneous Lichen Planus

Lichen planus is chronic and comparatively collective inflammatory mucocutaneous disease. The histopathological features of oral lichen planus were described as comparable to those of cutaneous lichen planus(CLP). Among those saw-toothed rete ridges are introduced as less important histopathologic features of idiopathic OLP in contrast to CLP. Accordingly, existing study aimed to estimate existence of saw tooth rete ridges in OLP in comparison to CLP. In this retrospective cross-sectional study, 56 H&E stained slides with clinical and histopathological diagnoses of OLP were randomly collected from the archive of the oral pathology laboratory. CLP cases were selected randomly from a private pathology laboratory and were evaluated for the presence of saw-toothed rete ridges. Collected data were evaluated using Chi-square &Fisher's exact test in SPSS 24 at an error level of 0.05%. Chi-square test did not show a substantial difference between oral & cutaneous groups in terms of the shape of the rete ridges (p = 0.511). Outcomes of existing study showed that saw tooth rete ridge was seen in OLP similar to CLP. Future studies concerning clinical subtype and type of keratosis are recommended.


Introduction
Lichen planus is chronic and relatively common mucocutaneous disease which is considered an autoimmune disease because it is believed to be the outcome of immunologic T-cell destruction of basal cells. Lichen planus was first described in 1869 by British physician Wilson Erasmus, as T-cell-mediated autoimmune disease involving skin, hair, eyes, mucous membranes, & nails, even though the exact target antigen in this process is not yet understood 1,2 Cutaneous lichen planus (CLP) typically comprises flexor surfaces of extremities & benevolences as insignificant multiple itchy violaceous papules with no particular pattern in middle-aged adults. Oral lichen planus (OLP) can be originate in 53.6% of CLP patients and sometimes OLP might be only clinical demonstration of disease. 3 The global prevalence of oral lichen planus has been estimated at 0.89% among populations in one systematic review study. 4 Lichen planus is identified in oral mucosa in forms of idiopathic lichen planus, drug-induced hypersensitivity reaction, localized contact hypersensitivity reaction to dental amalgam, oral lupus erythematous, chronic graft versus host disease which can only be differentiated by history and clinical findings.
Idiopathic oral lichen planus involves the oral mucosa mostly seen in middle-aged women involving buccal mucosa, dorsal surface of the tongue, and gums. 1,2 It is characterized clinically as symmetric bilateral lesions in three main clinical presentations: 1-reticular or keratotic 2-erythematous or erosive and 3-ulcerative. Histopathological structures of idiopathic oral lichen planus(OLP) and hypersensitivity type lichenoid mucositis were described as similar to those of cutaneous lichen planus(CLP) including hyperkeratosis, epithelial acanthosis or atrophy, basal cell liquefaction degeneration and sawtoothed rete ridges. 1,2,3 However hydropic basal cell degeneration or squamatization of basal cell layer & lymphocytic band at the interface often with the blurring of the interface is believed to be the main microscopic criteria for OLP. Whilst spongiosis, leukocyte exocytosis, colloid body formation, postinflammatory hyper melanosis and saw-toothed rete ridges are introduced as less important histopathologic features of idiopathic OLP. 3,1,5,6 Although in the study of Kashyap et al, saw-toothed rete ridges are introduced as a major microscopic criterion.. 7 Consequently existing study intended to estimate& equate presence of saw tooth or pointed rete ridges in and between OLP and CLP.

Materials and Methods
In this retrospective cross-sectional study, 56 samples of oral lichen planus (n=43) and cutaneous lichen planus (n=13). Oral samples were selected from the archives of the pathology department of Isfahan Azad Dental School and cutaneous samples from a private pathology laboratory in Isfahan under the ethics of Isfahan Azad dental school. The H&E stained slides of each sample were observed using a light microscope (Nikon, Japan) with a magnification of 100 and the shape of rete ridges was evaluated and categorized into two group's smooth /blunted rete ridges or hyperplastic /sawtooth shape rete ridges. Collected data were scrutinized using Chi-square & Fisher's exact test in SPSS 24 at an error level of 0.05%.

Results
The shape of rete ridges in oral lichen planus was blunted in 21 cases (48.8%) and saw tooth in 22 cases (51.2%) ( Figure 1). The Chi-square test did not illustrates substantial differences between two types of blunt or sawtooth-shaped rete ridges in oral lichen planus samples (p = 0.879). Fig. 1: Sawtooth shape rete ridge (A, H&E 100 ) and blunt or smooth rete ridge ( B, H&E 400) in Oral lichen planus The shape of rete ridges in cutaneous lichen planus was blunted in 5 cases (38.5%) and sawtooth in 8 cases (61.5%) (Figure 2). The Chi-square test did not illustrates substantial differences between two types of blunt and sawtooth shape rete ridges in cutaneous samples (p = 0.405).
The Chi-square test did not illustrates substantial differences between oral & cutaneous groups in terms of shape of rete ridges (p = 0.511) ( Table 1).

Discussion
The classic histopathological features of cutaneous lichen planus are dense, continuous, & band-like lymphohistiocytic infiltrate at dermal-epidermal junction in conjunction with epidermal changes such as hyper (ortho) keratosis, hyper granulosis, basilar vacuolar degeneration and sawtooth appearance of rete ridges. In oral mucosal lesions, epithelial alterations are fewerprecise compared to CLP and it has been said that rete ridges do not exhibit characteristic prominent sawtooth pattern 3 As we know rete ridges or rete pegs are epithelial extensions into the connective tissue. The morphology of the rete ridge is thought to be directly related to the mechanical pressures on the epithelium. Different morphology of rete ridges is seen among some oral mucosal lesions which can be diagnostic for pathologists. This variation in rete ridge morphology might be related to external mechanical and internal pressures due to epithelium proliferation by activation of ERK 1 / 2 protein kinase, production of matrix metallo proteinases, dissolution of basement membrane and migration of keratinocytes to connective tissue play a significant role in the morphology of rete ridges 8 However Lynch et al believe inflammation might play role in the morphology of rete ridges which was not reported as an etiologic factor for cell proliferation and subsequent changes in the morphology of rete ridges in the study of Kaplan and Hirshberg who showed no significant differences between PCNA and Ki 67 proliferation marker expression in epithelium of keratocyst with inflammation. 9,10 Our study intended to estimate & equate shape of saw-toothed or pointed rete ridges in OLP with CLP. Aminzadeh et al had previously reported saw-toothed rete ridges in Oral lichen planus. 8 Tamgadge showed that atrophy of epithelium leads to pointed rete ridges which are known as sawtooth rete ridges. 3,14 Hence according to the obvious disagreement regarding serrated, pointed or sawtooth-shaped rete ridges in OLP, it is best to perform further studies with equal sample sizes concerning clinical subtype (hyperplastic or atrophic) and type of keratosis(ortho with granular layer or para without granular layer) in future studies which were the limitations of present study.

Conclusion
Results of existing study showed that saw tooth rete ridge was seen in OLP similar to CLP. Future studies concerning clinical subtype and type of keratosis are recommended.