Primary acquired melanosis (PAM) is an acquired noncystic, flat, patchy or diffuse, tan to brown pigmentation of the conjunctival epithelium. The condition is usually unilateral or asymmetric if bilateral and is most often seen in light-skinned individuals (Fig 12-11). Secondary acquired melanosis has a similar appearance but is associated with systemic disease (eg, Addison disease), previous radiation, or pregnancy or is secondary to another conjunctival lesion (eg, squamous papilloma or carcinoma). Table 12-3 compares the various pigmented lesions of the conjunctiva.
Changes in the size of PAM may be associated with inflammation or may be the result of hormonal influences. Complete examination of the ocular surface (including double eversion of the upper eyelid) is essential in any patient with conjunctival pigmentation; see the following section for management of these lesions.
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Shields JA, Shields CL. Conjunctival melanocytic lesions. In: Eyelid, Conjunctival, and Orbital Tumors: An Atlas and Textbook. 3rd ed. Philadelphia: Wolters Kluwer; 2016: 307–348.
Most cases of PAM are benign, but a substantial minority of cases may progress to melanoma. It is difficult to predict which lesions may progress, but clinical findings such as larger size (3 clock-hours or more) and caruncular, forniceal, or palpebral location portend a worse prognosis. Two clock-hours or less of conjunctival involvement is associated with a lower risk of malignant transformation; involvement of more than 2 clock-hours is an indication to remove the lesion for histologic diagnosis. Other worrisome signs include progressive enlargement, a nodular component, feeder vessels, and thickening.
The most important finding in predicting progression is the presence of cellular atypia, which can be determined only by excisional biopsy. As such, suspicious lesions should be removed and sent for histologic examination and immunohistochemistry. See BCSC Section 4, Ophthalmic Pathology and Intraocular Tumors, for a more detailed discussion of the evolving histologic classification of intraepithelial melanosis.
A, Diffuse primary acquired melanosis of the bulbar conjunctiva. B, Primary acquired melanosis of the palpebral conjunctiva.
(Courtesy of Kathryn Colby, MD, PhD.)
As PAM without atypia has little malignant potential, it may be followed (with examination every 6–12 months). PAM with mild atypia has a minimal risk of malignant transformation but should be followed more closely. However, PAM with moderate to severe atypia carriers a significant risk of progression to melanoma; thus, every effort should be made to eliminate all conjunctival pigment in patients with moderate to severe atypia. If the pigmentation is diffuse and not amenable to complete excision, adjuvant topical chemotherapy with mitomycin C may be useful to treat the entire ocular surface. The surgeon should exercise care in performing intraocular surgery in a patient with untreated ocular surface neoplasia, as violation of the Bowman layer may lead to tumor seeding within the corneal stroma and internal structures of the eye. Secondary acquired melanosis has no significant risk of progression to melanoma.
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Colby K, Bhat P, Novais G, Jakobiec FA. Recurrent primary acquired melanosis with atypia involving a clear corneal phacoemulsification wound. Cornea. 2011;30(1):114–116.
Jakobiec FA. Conjunctival primary acquired melanosis: is it time for a new terminology? Am J Ophthalmol. 2016;162:3–19.
Shields JA, Shields CL, Mashayekhi A, et al. Primary acquired melanosis of the conjunctiva: risks for progression to melanoma in 311 eyes. Ophthalmology. 2008;115(3):511–519.
Sugiura M, Colby KA, Mihm MC Jr, Zembowicz A. Low-risk and high-risk histologic features in conjunctival primary acquired melanosis with atypia: clinicopathologic analysis of 29 cases. Am J Surg Pathol. 2007;31(2):185–192.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.