Primary Acquired Melanosis

Conjunctival primary acquired melanosis (PAM) appears clinically as a flat and variegated brown, usually monocular, lesion ranging from golden brown to dark chocolate, which may involve any area of the conjunctiva. PAM typically occurs among adults and older people. PAM may remain stable for long periods or may grow. Lesions may “wax and wane.” Because of this, the lesion’s clinical borders often cannot be identified accurately. A lesion designed as PAM clinically may feature no atypia histologically (PAM without atypia) or may feature histological melanocytic atypia (PAM with atypia). PAM without atypia does not progress to melanoma, whereas PAM with atypia should be considered a precursor. PAM with atypia may be subdivided into lower and higher-risk lesions for melanoma recurrence and progression based on the atypical melanocytes’ distribution and cytological features. Recently, the term “conjunctival melanocytic intraepithelial lesion” (C-MIL) was described in the fifth edition of the WHO Classification. The histological criteria for classifying lesions by PAM and C-MIL are identical. There are no clinical criteria by which ophthalmologists can predict the histological diagnosis. Therefore, when PAM is suspected clinically, the lesion should be biopsied. A small lesion should be completely excised. Incisional biopsies (also known as “map” biopsies) provide a way to sample diffuse or widespread lesions at various sites of clinical concern. Besides surgical excision, cryotherapy may be performed. Topical mitomycin C, chemotherapy, and topical interferon α-2b effectively treat PAM with atypia.