Consider systemic infections, such as syphilis and tuberculosis, in patients with intermediate and otherwise non-diagnostic forms of posterior uveitis. We tend to test for syphilis in virtually all patients with these forms of uveitis, because the test is risk-free and inexpensive, and because missing a diagnosis of syphilis can have such serious implications for the overall health of the patient. Remember, however, that less specific tests for syphilis, such as the RPR and VDRL, may be negative in up to 30 percent of patients with syphilitic uveitis. The RPR and VDRL may also be falsely positive in patients with collagen-vascular disease. Lyme disease can also cause intermediate or posterior uveitis, but we forego testing unless the patient gives a definite history of tick exposure or of erythema migrans.
Intraocular malignancies are far less common uveitis mimics.
In young children, neoplastic masquerades include retinoblastoma, leukemia and juvenile xanthogranuloma. Retinoblastoma presents under 3 years of age in 90 percent of children, usually suggested by a milky or chalky-white vitreous, and retinal or iris infiltrates. An ultrasound or CT scan can sometimes show calcific densities in these tumors. Ocular leukemia, by contrast, tends to occur at a slightly older age, and may present as anterior uveitis or as yellow-white retinal, subretinal, perivascular, choroidal or optic disc infiltrates. Any patient with leukemia who presents with uveitis should be presumed to have ocular leukemia until proven otherwise.