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  • Cases Around the World: Less Fog, More Light — Toxoplasmosis in Latin America

    Chorioretinal scars Toxoplasmosis

    White lesions in the retina should always open up a differential diagnostic approach for inflammatory or infectious causes.

    Yet in our international communities across the world, the “Most Wanted” list always starts and ends with ocular toxoplasmosis and especially retinochoroiditis, due to its highly prevalent exposure rates. This means that your relationship with this disease and its many clinical presentations and courses starts early on during training and keeps you humble as your practice develops. 

    Fortunately, it also means that there could be a few insights you can share with international YOs eager to shed some light into the fog.

    A Parasite of Many Faces

    You may already be familiar with the classic clinical history of recurrent posterior uveitis that presents with an active retinal necrosis near a chorioretinal scar. But that does not mean it will always be this way.

    Sudden visual loss with a varying degree of ocular pain, photophobia or floaters should raise alarms. The symptoms are in direct proportion to the location of the lesion and the amount of vitritis, some of which could spill over to the anterior segment and cause ocular hypertension or granulomatous precipitates. 

    This is mostly a clinical diagnosis so a thorough dilated fundus exam is key to evaluate the inflammatory activity of the suspicious white, fluffy retinal lesion and the presence of adjacent, peripheral or even contralateral chorioretinal scars. Less common findings of vasculitis, multifocal lesions or optic neuritis may be present in immunocompromised patients. 

    Know Your Options

    Due to the higher virulence of regional toxoplasma gondii strains and the serious risk that undetected recurrence leads to visual loss, you should keep your treatment threshold lower than usual. There are many treatment schemes available with comparable efficacy so your choice should be mostly determined by availability, access and individual patient characteristics. 

    I personally opt for oral trimethoprim-sulfamethoxazole (TMP-SMX) and a dose of subtenon triamcinolone since it is less likely to be associated with the systemic side effects of classic triple therapy (oral pyrimethamine, sulfadiazine and prednisone). For instance, there is no need to add prophylactic folinic acid or actively monitor for bone marrow suppression. On top of that, adherence to treatment may be simplified with fewer medications. Consider options such as oral or intravitreal clindamycin for pregnant patients or high-risk macular lesions. 

    Consider Imaging Early

    OCT can be valuable to rule out or follow up on macular edema, examine suspicious solitary lesions, determine inflammatory reactivation on cases of absent vitritis or even consider other complications associated with severe retinal necrosis. The use of fundus angiography can further characterize widespread vasculitis (think arterial, venous or occlusive) to get clarity on the diagnosis or prognosis. If your practice setting allows, remember that even fundus photography is a helpful tool in follow up and patient reassurance.

    Beware of Recurrence and Complications

    They say time heals all wounds but these ones have a tendency to come back. Recent literature places recurrence around 50% on average and even higher in Latin America. 

    At first, it’s wise to schedule follow-up visits based on the severity of inflammation and the location of the lesion until a clear recovery trend is established. Remember to give clear advice on how to identify new episodes and the importance of seeking prompt care. Patients with a history of recurrence could benefit from long term antimicrobial therapy with trimethoprim-sulfamethoxazole (TMP-SMX) every other day for one year.

    Persistent vitritis, cataract, macular edema, retinal neovascularization, glaucoma or hyaloid traction/retinal detachment could all be possible complications. Keep them in mind during subsequent evaluations, especially in torpid clinical courses.

    Don’t Let the Curveballs Strike You Out

    First episodes, solitary lesions, immunosuppressed patients, hazy media are all circumstances where a straightforward diagnosis may be challenging. Broaden your differential with other infectious causes such as tuberculosis, bartonellosis, syphilis, HIV or other viral retinitis.

    Consider them in your work up and be vigilant of the initial response to therapy. These and other inflammatory etiologies can have rapidly progressing courses that require close observation and swift action.

    Headshot of Eduardo J. Viteri, MD About the author: Eduardo J. Viteri, MD, is a vitreoretinal surgeon in hospital-based and private practice in Guayaquil, Ecuador. He is a member of the Academy's YO International Subcommittee and co-chair of the Pan-American Association of Ophthalmologists’ YO Committee.