Clinical and morphological characteristics of lichen planus and lichenoid drug eruption of the skin

Background: Lichen ruber planus (LP) and lichenoid skin reaction (LSR) are clinically and histologically similar. The performance of histological diagnosis in these diseases remains controversial. Materials and methods: We prospectively studied 33 patients with clinical manifestations and histological signs of the classic form of LP and LSR to assess the accuracy of an isolated histological LP and LSR examinations and to identify a variety of microscopic features. Each histological study was conducted by a pathomorphologist, who was blinded to the patients’ clinical characteristics and diagnosis. Results: Isolated histopathological examination made it possible to make a correct diagnosis in 25 (75%) of 33 patients: in particular, the diagnosis of LRC was established in 10 (30%), CPL-in 15 (45%) cases. Based on a combined assessment of histological and clinical data and response to therapy, the final diagnosis was established in 30 (91%) of the 33 patients who were divided into two groups. The first group comprised 18 patients diagnosed with LSR, and the second group comprised 12 patients diagnosed with the classic form of LP. Conclusions: Through this investigation, some differences in these diseases based on their clinical and pathomorphological features were identified. The diseases were characterized by different typical localizations and lesion sizes. The pathomorphology of both diseases is represented by lichenoid type of interface dermatitis.