Histopathologic evaluation of mast cells in reticular and erosive oral lichen planus using toluidine blue staining

Introduction: Oral Lichen Planus (OLP) is one of the most common mucocutaneous lesion, and its etiologic factors have not been elucidated yet. OLP has two different clinical forms including reticular and erosive. Mast cells function in non-specific immunology is an etiologic factor involved in the formation of lichen planus. This study aimed at determining the pattern of mast cells presence in clinical forms of reticular and erosive oral lichen-planus in basal, epithelial, and superficial connective tissue layers. Methods: The study population in this retrospective research included archival histopathological files in Oral and Maxillofacial Pathology Department, Faculty of Dentistry, Tehran University of Medical Sciences. A total number of 53 paraffin-embedded blocks consisting of 18 reticular and 17 erosive OLP samples were included in the study. Four-micron sections were prepared for toluidine blue staining. Mast cells were counted in ten fields of light microscopy at magnification of 400 in epithelial, basal, and superficial connective tissue layers, and the mean number of mast cells in each layer was calculated. Mann-Whitney and Friedman tests were used to analyze the data while p-values less than 0.05 were considered significant. Results: The mean number of mast cells was 1.85&plusmn;2.9 in reticular and 2.02&plusmn;3.18 in erosive groups. The mean count of mast cells in epithelial, basal, and connective tissue layers were 0.23&plusmn;0.31, 0.34&plusmn;0.45, and 4.98&plusmn;3.28, respectively, in reticular lichen planus, and 0.21&plusmn;0.25, 0.23&plusmn;0.38, and 5.53&plusmn;3.31, respectively, in erosive lichen planus. There was no significant difference between reticular and erosive forms of OLP and between epithelium and basal layers in terms of mast cells count (P=0.474, P=0.148, respectively), whereas a significant difference existed between epithelial and connective tissue layers (P<0.001). Conclusion: The number of mast cells in reticular and erosive forms of OLP was higher in connective tissue than epithelium. Regardless of tissue layer, mast cells count was higher in erosive than reticular form of lichen planus.