21

QUESTION

HOW DO I DISTINGUISH ONE PIGMENTED LESION FROM ANOTHER?

Amy C. Schefler, MD
Ryan S. Kim, BA

The differential diagnosis of a pigmented choroidal lesion includes choroidal nevus, choroidal melanoma, congenital hypertrophy of the retinal pigment epithelium (CHRPE), melanocytoma, extramacular disciform lesion, and other rarer entities. Given that a missed uveal melanoma diagnosis can be life-threatening, both general ophthalmologists and retinal specialists should be well versed in distinguishing these lesions from each other.

Choroidal Nevi and Melanoma

Pigmented choroidal nevi are extremely common in the White population, and it is estimated that 10% to 15% of adults have at least one such lesion. Uveal melanoma, on the other hand, is a rare disease with only 1200 to 2000 cases/year in the United States. Thus, the task of distinguishing a rare, but malignant lesion from many benign lesions is challenging. Funduscopic examination with fundus photography and ophthalmic ultrasound have long served as the core clinical diagnostic modalities in this endeavor. Gene expression profile (GEP) testing and multiplex ligand-dependent probe amplification, on the other hand, have become increasingly crucial in recent years for the management of uveal melanoma.^1,2

While clinical findings via funduscopic exam and ultrasound are still an important part of monitoring choroidal lesions, both multiplex ligand-dependent probe amplification and GEP can help predict which melanoma patients will develop metastatic disease (Table 21-1). Thus, clinicians can use the genetic information to determine the prognosis and build a corresponding treatment regimen.

Traditionally, various clinical features have been thought to be associated with growth of choroidal nevi into uveal melanoma, including orange pigmentation, presence of subretinal fluid and drusen, vascularity on B-scan ultrasonography, and low-to-medium internal reflectivity on A-scan ultrasonography. Recent data have also shown that increasing basal diameter confers additional poor prognosis in lesions with high-risk genomics.⁴ Specifically, uveal melanoma that was classified as GEP Class 2 and had a basal diameter of less than 12 mm showed better prognosis than the larger counterpart.⁵ Conversely, many of the clinicopathologic factors have recently been demonstrated not to exhibit a statistically significant association with GEP class and metastatic risk.⁶

Given that recent studies demonstrate that clinical features are not reliably predictive of the development and progression of uveal melanoma, performing a biopsy at the time of treatment for uveal melanoma has become an indispensable source of information for determining risk for metastasis. Genetic analysis may be extremely useful for confirming the diagnosis of melanoma and determining the prognosis. Moreover, based on the newer molecular data, the Class 1A genomic signature that is more common in smaller lesions will progress molecularly to Class 2 eventually in some cases. Therefore, clinicians are advised to treat patients as early as possible in order to minimize metastatic death.⁷ It is best to consider both clinical features as well as genomic information for each melanoma.

Weighing all of the clinical risk factors associated with a particular lesion takes clinical experience and judgment. As a general rule, we feel that a patient with one or more high-risk features should be referred for assessment by an ocular oncologist (Figure 21-1). Small, flat, peripheral lesions (Figure 21-2) with no orange pigment and with associated drusen can be observed and documented with serial photography by a general ophthalmologist or retina specialist. When in doubt, an ophthalmologist who has limited experience with tumors should always refer a patient to an ocular oncologist for an evaluation.

Other Pigmented Choroidal Lesions

Other pigmented lesions that are important to include in the differential diagnosis of choroidal melanoma are CHRPE, melanocytoma, and extramacular disciform lesions associated with peripheral exudative hemorrhagic chorioretinopathy. These lesions are important to distinguish from choroidal nevi and melanoma. Distinguishing features are outlined in the following sections.

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