Incidence of Primary Acquired Melanosis Within Pterygium Specimens: A 13-Year Retrospective Study in a Canadian Tertiary Center

Purpose: Primary acquired melanosis (PAM) and pterygia are ocular surface lesions associated with sun exposure, with distinct clinical and histopathological features. This study aims to determine the incidence of PAM within pathology specimens of presumed benign pterygium cases at a tertiary center in Montreal. Methods: A retrospective cohort study of all consecutive patients undergoing pterygium excision at a tertiary care center between 2010 and 2023 was performed. Pathology reports of excised pterygium samples were reviewed, with data collected on age, sex, and histopathological findings. Ethics approval was obtained from the institutional review board, and no patients were excluded. Results: Among 1695 excised pterygia, 1277 (75.3%) specimens were submitted for pathology. Most were confirmed as pterygia (1230 samples, 96%). There were 40 unexpected findings (3.2%) including nevus or melanosis (13 cases), Salzmann nodules (5 cases), and ocular surface squamous neoplasia (4 cases). Two cases of PAM were identified: one with atypia in a 68-year-old French-Canadian man and another with no atypia in a 74-year-old Greek man. Conclusions: The low incidence of PAM observed highlights its rarity in presumed benign pterygium specimens. However, the identification of PAM with atypia emphasizes the need for routine pathological evaluation of all excised pterygia, even in the absence of clinical suspicion, due to the significant differences in management required for PAM.