Histological criteria for grading of atypia in melanocytic conjunctival lesions

Aims: To develop a standardised protocol for grading atypia in melanocytic conjunctival lesions (MCL), mainly primary acquired melanosis (PAM) and inflamed juvenile conjunctival naevi (IJCN) and to establish prognostic parameters for progression to malignant melanoma (MM). Methods: A retrospective non-randomised study of 304 patients with MCL was conducted. Histological slides of MCL diagnosed as conjunctival naevus (CN; 222 cases), PAM (42 cases), and IJCN (40 cases) were reviewed. A scoring method of atypia was developed according to the following histological parameters: nest cohesion, melanocytic hyperplasia, nuclear features, and pagetoid spread. Lesions were scored according to the number of criteria as mild (1-2), moderate (3-4) and severe (5-8). Results: Nineteen PAM lesions showed mild (n=8), moderate (n=4), and severe (n=7) atypia. The remaining PAM lesions were without atypia. IJCN cases showed architectural disorder only. Neither architectural disorder nor cytological atypia were found in the CN. There were no recurrences in the IJCN and PAM lesions without and with mild atypia, while two PAM with moderate and two with severe atypia recurred. Three cases (two of which had a history of recurrent PAM with severe atypia) progressed to MM. The criteria for evaluation of atypia were found to be significantly associated with the clinical outcome (p<0.0001). Conclusion: The standardised histological scoring protocol of MCL is reliable, and may reduce the risk of confusing a benign MCL, such as IJCN, with one that is potentially preneoplastic. It may also prove useful in predicting which PAM lesions will progress to MM.