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Observer agreement in the diagnosis of oral lichen planus using the proposed criteria of the American Academy of Oral and Maxillofacial Pathology.

BACKGROUND
Oral lichen planus (OLP) is a common chronic inflammatory condition with an undefined malignant transformation potential. There have been many attempts at providing a specific definition of OLP without conclusive outcomes. A new set of diagnostic criteria was proposed in 2016 by the American Academy of Oral and Maxillofacial Pathology (AAOMP) in an endeavour to resolve this issue, and this has not yet been evaluated. This study aimed to assess the utility of AAOMP proposed criteria for the diagnosis of OLP.


METHODS
Five pathologists blindly assessed a cohort of 215 digital whole slide images (WSI) obtained from haematoxylin and eosin stained microscopic slides. Forty-six WSI were included twice to assess the intra-observer agreement. Included cases were diagnosed clinically as either OLP or oral lichenoid reaction. Each pathologist was asked to utilize the AAOMP histopathological criteria while assessing slides. The variations in diagnoses were assessed by unweighted kappa statistics.


RESULTS
The level of intra-observer agreement was very good (0.801 to 0.899). The level of inter-observer agreement among the observers varied from good (0.658) to very good (0.842) when the responses were categorized as evident/compatible OLP versus no OLP, and was good (0.62 to 0.725) when the responses were categorized as evident OLP, versus compatible OLP, versus no OLP. The clinico-pathological correlation was 87.6%.


CONCLUSION
A reliable level of agreement can be achieved by pathologists for the diagnosis of OLP using the AAOMP criteria for differentiation between lichenoid and other conditions. There are still limitations in discriminating OLP from oral lichenoid lesions microscopically.