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Differentiation of wet AMD and PCV is crucial
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Most patients who present with painless, progressive loss of vision and metamorphopsia, with evidence of subretinal hemorrhages and exudates in the macular area on fundus examination, have wet or exudative age-related macular degeneration.
Experienced clinicians know that, in the U.S., horses are much more common in the countryside than zebras, and wet AMD is a horse, not a zebra. The same clinicians also know that zebras occasionally present in their clinics, and polypoidal choroidal vasculopathy (PCV), first described by Dr. Lawrence Yannuzzi in 1982, is one of the zebras to rule out in the patient who presents with a clinical course and findings consistent with wet AMD. Other conditions that belong in the differential diagnosis of wet AMD include central serous chorioretinopathy, ocular histoplasmosis syndrome, pathologic myopia, choroidal injury, angioid streaks and, perhaps, Best’s vitelliform maculopathy and Stargardt disease.
The index of suspicion for PCV should be higher for a younger black or Asian patient presenting with symptoms and signs of wet AMD. Also, on fundus examination, the subretinal blood and exudates are often in multiple locations surrounding the peripapillary region rather than isolated to the macula. If one looks carefully, there are no drusen. OCT alone, or even when combined with fluorescein angiography, is insufficient to confirm the diagnosis of PCV. Indocyanine green angiography is the gold standard test. I suspect that the new OCT angiography just becoming available may also suffice, but ICG and OCT angiography are rarely available in the comprehensive ophthalmologist’s office.
An astute clinician who observes an atypical-looking presentation of what could be wet AMD with multiple lesions and no drusen in a younger black or Asian patient can play a positive role in that patient’s future by referring him or her to an experienced retina specialist, as the treatment is different and, if initiated early, very effective. According to the EVEREST study, photodynamic therapy applied after the intravenous injection of verteporfin either alone or in combination with intravitreal injections of an anti-VEGF agent can result in dramatic visual improvement, which in many cases approaches a cure. While some retina specialists argue PCV and wet AMD are variants of the same pathologic process, the preferred therapy using PDT with intravenous verteporfin supports the importance of differentiating the two entities.