Various clinical pathological features of OLP have been reported. Considering the diversity of OLP manifestations, OLPFCs may be not uncommon clinical features; however, there is the minimal clinical literature regarding OLPFCs. Severe OLPFCs that cause RMO may be difficult to diagnose and treat; therefore, information regarding the histopathological features and treatment strategies of OLPFCs may be useful for clinicians.
OLP is considered a precancerous lesion and was classified as an oral potentially malignant disorder by the 2017 World Health Organization guidelines (Speight et al. 2018). OSF is also considered an oral potentially malignant disorder. OLP that has progressed to the stage of OLPFCs is similar to exacerbated OSF in that it causes RMO; however, there are some differences in etiology and histological features between OLPFCs and OSF.
Histopathologically, the pathogenesis of OLP is mainly centered on the epithelial lamina propria boundary (subepithelial layer to basal layer). In contrast, pathological alteration in OSF begins in the lamina propria and secondarily involves the epithelium (Rajendran 1994). Given these characteristics, the central locations of fibrotic changes may differ between OLPFCs and OSF, such that OLPFCs occur mainly in the subepithelium, while OSF may occur throughout the connective tissue. Masson's trichrome staining is effective for diagnosis because the site of collagen formation can be clarified.
In the present patient, the immunohistochemical staining results were negative for CK13, positive for CK17 within the epithelium layer, and positive for Ki-67/MIB-1 primarily in the basal layer. In patients with OSF, the expression of CK13 in the epithelium tends to decrease (Kuo et al. 2006), while the expression of CK17 in the suprabasal layer increases (Lalli et al. 2008) and Ki-67/MIB-1 exhibits basal layer expression and intense nuclear staining (Humayun and Prasad 2011). These immunohistochemical staining findings may be similar between OLPFCs and OSF. Previous reports suggest that the severity of OSF is associated with the degree of CK17 or Ki-67/MIB-1 staining; a similar assessment may be possible for OLPFCs.
With respect to treatment methods, patients with early OSF can be treated by local injection of triamcinolone acetonide, while patients with advanced OSF require surgical intervention (Khanna and Andrade 1995). OSF surgery may require deep excision and reconstruction, presumably because severe OSF can infiltrate the muscular layer (Rooban et al. 2005). In contrast, OLPFCs in our patient could be treated simply by band-shaped indurated mucosal excision and Z-plasty, without excision of the muscular layer. The center of fibrotic changes is more superficial in OLPFCs than in OSF; therefore, the muscular layer may be mostly intact and not require resection.
It is uncommon to routinely perform biopsies of OLP lesions unless potential malignant changes are suspected, or to confirm a differential diagnosis. However, considering the potential for progression to OLPFCs, excision or biopsy for histopathological evaluation (including specialized staining) may be warranted. There have been no research reports regarding histopathological specialized staining and surgical treatment for OLPFCs; hence, there is a need for additional case reports regarding patients with OLPFCs.