Oral Lichenoid Reactions:
Oral lichenoid reactions (OLRs) or oral lichenoid lesions (OLLs) are clinically and histologically similar to lichen planus63. Lichen planus is a severe chronic inflammatory disorder that can affect the skin and lining mucosa, including oral, oesophageal, and genital mucosa. Oral lichenoid reactions are reported to affect about 1-2% of the population, with women more commonly affected than men 10. Oral lichen planus usually occurs on the buccal mucosa, gingivae, and tongue. Clinical presentations of oral lichenoid reactions vary from white striated reticular patterns to white and red confluent plaques, ulcerations, and erosions. A case was reported with pembrolizumab-induced oral graft versus host disease (GVHD) or lichen planus like lesion 144.
Pathogenesis: While the etiology of oral lichenoid reactions is unknown, but it is supposed to be an immunologically T-lymphocyte mediated reaction to the keratinocytes present on the basal surface of the skin or mucosal membrane 63.
Clinical presentation : Eighteen cases of oral lichenoid reactions were reported with anti-PD-1/PD-L1 immunotherapy. Cases associated with various drugs are as follows, four with pembrolizumab145, 146, fourteen with nivolumab146-150. The time from initiation of anti-PD-1/PD-L1 treatment to the development of oral lichenoid reactions ranges from two weeks to four years with the dosing regimen of pembrolizumab: 200 mg /2mg/kg I.V., every 3 weeks, nivolumab = 200 mg I.V. every 15 days, 480 mg every 4 weeks, 240 mg I.V. q2w, 3 mg/kg I.V. q2w. Oral lichenoid reactions occur in patients within the age of 26-93 years (mean=62). The disease arises on the buccal mucosa, soft palate, ventral and dorsal aspect of the mouth and tongue, labial mucosa, gingivae, and the hard palate. Clinical and histological findings of the disease include the occurrence of a white striated reticular pattern to red confluent plaques erosion, wickham striations ulcerations, or erosions.
Treatment: Patients responded well to the topical steroid therapies (prednisone, methylprednisone) 148 when prescribed for oral irAEs. Other treatments have also been evolved which include betamethasone cream 147, dexamethasone 0.1 mg/ml solution 149, fluocinonide 0.05% gel, Oracort dental paste, triamcinolone acetonide 0.1% paste 146.