Primary acquired melanosis of the conjunctiva

Primary acquired melanosis (PAM) presents as a unilateral patchy area of conjunctival pigmentation mostly found in middle-aged or elderly white patients. Because PAM has the potential of becoming malignant, it is important to recognize PAM and to rule out other causes of pigmented lesions. The presence or absence of atypia is helpful in determining the potential for malignancy, because PAM without atypia is usually benign, whereas PAM with atypia may convert into a conjunctival melanoma. If atypia is present, the presence or absence of epithelioid cells and the pattern of intraepithelial growth are the main factors in determining the likelihood of neoplastic transformation. However, atypia can only be determined with histopathologic examination. Therefore, a biopsy is usually recommended.

A 72-year-old white man presented for his annual examination with no visual complaints. His ocular history was remarkable for early cataracts and for a choroidal nevus. Slit lamp examination found a large dark area of elevated conjunctival pigmentation at the medial canthus that extended onto the superior bulbar conjunctiva and superior palpebral conjunctiva in the left eye. No conjunctival pigmentation had been noted previously. Results of a biopsy indicated primary acquired melanosis with atypia. The lesion was surgically excised, and the conjunctiva was reconstructed with an amniotic membrane graft. The patient was subsequently treated with topical 5-fluorouracil chemotherapy. There have been no signs of recurrence to date after his treatment.

Because of the potential for malignancy, biopsies of all cases of primary acquired melanosis are indicated. If atypia is present, treatment options include local excision, cryotherapy, and topical chemotherapy.