Primary Acquired Melanosis (PAM): Why Some Flat Conjunctival Pigment Needs Oncology Input

Primary acquired melanosis (PAM) is flat, patchy brown conjunctival pigmentation that typically develops in adulthood. Unlike a classic conjunctival naevus (often cystic and long-standing), PAM may spread across “clock-hours” and can be associated with cellular atypia, which is the key driver of melanoma risk. ¹

The most important practical risk signals are:

• Extent (more clock-hours = higher risk)
• Change (new spread, darkening, thickening, nodularity)
• High-risk phenotype (multifocal, poorly defined borders, new feeder vessels)

Histology stratifies prognosis. In a large ocular oncology series, PAM without atypia or with mild atypia showed essentially no progression, whereas severe atypia carried a measurable risk of melanoma transformation. ¹ ² For this reason, suspected PAM, especially if extensive or changing, should not be “watched casually.” It needs high-quality baseline photography, clear documentation of involved clock-hours, and early ocular oncology involvement when atypia is suspected or the lesion is diffuse. ³

Management can range from structured observation (small, stable, low-suspicion lesions) to excision with cryotherapy and/or topical chemotherapy (for diffuse disease), guided by specialist assessment. ³

References

1. Shields JA, Shields CL, Mashayekhi A, Marr BP, Benavides R, Thangappan A, et al. Primary acquired melanosis of the conjunctiva: experience with 311 eyes. Ophthalmology. 2008;115(3):511-519.e2. doi:10.1016/j.ophtha.2007.07.003. PMID: 17884168.
2. Folberg R, McLean IW, Zimmerman LE. Primary acquired melanosis of the conjunctiva. Human Pathology. 1985;16(2):129-135. doi:10.1016/S0046-8177(85)80249-4. PMID: 3972395.
3. Wong JR, Nanji AA, Galor A, Karp CL. Management of conjunctival melanoma and primary acquired melanosis. Clinical Ophthalmology. 2014;8:197-206. doi:10.2147/OPTH.S45987. PMID: 25580155.

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