Background: Cytomegalovirus (CMV) and Toxoplasma gondii both cause necrotizing retinopathy in immunosuppressed hosts. Because of the high prevalence of serum antibodies to these agents in the general population and the risks associated with retinal biopsies, diagnosis of these infections is usually based on clinical findings alone, but the two infections can be confused with one another because of similar clinical features. Accurate diagnosis is critical, however, because both diseases are treatable but require different medical therapies.
Methods: Case histories were reviewed for five immunosuppressed patients with necrotizing retinopathy, which was initially diagnosed incorrectly as CMV retinopathy but was subsequently found to be toxoplasmic retinochoroiditis. Correct diagnosis was based on retinal biopsy (2 cases) or rapid response to antiparasitic drug therapy (3 cases). Factors were sought that might help differentiate toxoplasmic retinochoroiditis from CMV retinopathy at presentation.
Results: In all cases, the character of retinal opacification (densely opaque, thick) and the appearance of lesion borders (smooth, nongranular) was different from that typically seen with CMV retinopathy. These cases also were characterized by prominent anterior chamber and vitreous inflammatory reactions (four of five cases) and relative lack of retinal hemorrhage. One patient subsequently developed CMV retinopathy; characteristics of the two lesions in the same eye highlighted the differences between these two infections.
Conclusion: Clinicians should consider ocular toxoplasmosis as a cause of necrotizing retinopathy in immunosuppressed patients and consider an empiric course of antiparasitic therapy for lesions with features described in this report.