52.1 Features
Toxoplasma retinochoroiditis is the most common cause of infectious posterior uveitis in immunocompetent individuals and is a result of congenital or acquired infection with the ubiquitous intracellular protozoan parasite Toxoplasma gondii. T. gondii is a widespread parasite that approximately 25 to 30% of the human population is infected with. Humans can get infected by the consumption of undercooked cyst-contaminated meat products or by sporulated oocysts, which can be found in water, soil, or vegetables. The parasite exists in different morphologic and metabolic stages, which are products of the parasite’s sexual cycle in the intestine of cats. After ingestion, the cysts (or oocysts) are disrupted and the bradyzoites are released into the intestinal lumen where they rapidly enter cells and multiply as tachyzoites. Ocular toxoplasmosis can result in a granulomatous panuveitis.
52.1.1 Common Symptoms
Symptoms include eye redness, pain, photophobia, floaters, and blurry vision. In some cases, toxoplasma retinochoroiditis may only have focal overlying vitritis, and hence, some patients with peripheral lesions may be largely asymptomatic.
52.1.2 Exam Findings
Variable based on the extent of involvement but may include keratic precipitates (▶ Fig. 52.1a), anterior chamber cell, scleritis, posterior synechiae, cataract, vitreous cell, vitreous haze, chorioretinal lesions, epiretinal membrane, intraretinal hemorrhages, neuroretinitis (▶ Fig. 52.1b), retinal vasculitis, choroidal neovascularization (CNV), and retinal detachment. Strabismus (often due to poor vision secondary to a macular lesion), nystagmus, and microphthalmia may be present in congenital toxoplasmosis.
Fig. 52.1 Clinical findings in ocular toxoplasmosis. (a) Granulomatous anterior chamber inflammation with mutton-fat keratic precipitates on the corneal endothelium. (b) Retinochoroiditis adjacent to the optic nerve with resulting disc edema with the evidence of a previous toxoplasma chorioretinal lesion with hyperpigmentation with the development of a new lesion adjacent to its border. (c) “Headlight in the fog” appearance resulting from a whitish area of retinitis seen through the vitreous haze.
The classic description of an active chorioretinal lesion is that of a “headlight in the fog,” which refers to the whitish focal area of necrotizing retinochoroiditis that is somewhat visible through the vitreous haze (▶ Fig. 52.1c). Inactive chorioretinal lesions appear as variable pigmented patches of chorioretinal atrophy (▶ Fig. 52.2). It is not uncommon to have reactivation of toxoplasma retinochoroiditis adjacent to a previous lesion in which case lesions in various degrees of evolution are noted. Immunocompromised individuals may have a more atypical presentation with large confluent areas of retinochoroiditis and simultaneous bilateral active disease. Lesions may also present as punctate outer retinal toxoplasmosis (characterized by multifocal, small lesions, which are located in the deep layers of the retina and retinal pigment epithelium. Patients with congenital toxoplasma retinochoroiditis are more likely to have bilateral and macula-involving lesions.
Fig. 52.2 Ultra-widefield imaging in inactive toxoplasma retinochoroiditis. (a) Multiple healed pigmented chorioretinal lesions are seen without overlying vitritis. (b) Autofluorescence reveals hypoautofluorescence of the lesions due to retinal pigment epithelium (RPE) loss. There is a rim of hyperautofluorescence around the nasal and macular lesions, which may be secondary to photoreceptor loss overlying intact RPE.
52.2 Key Diagnostic Tests and Findings
52.2.1 Optical Coherence Tomography
Active lesions may show disorganization of retinal layers (both inner and outer) in the region of retinitis and vitreous cells adjacent to the area of retinitis (▶ Fig. 52.3a,b). Inactive lesions typically show chorioretinal atrophy. Optical coherence tomography is also useful in detecting intraretinal and subretinal fluid that may be associated with CNV at the site of the chorioretinal lesion and may reveal epiretinal membrane formation with or without associated distortion of the retina.
Fig. 52.3 Multimodal imaging in toxoplasma retinochoroiditis. (a) Spectral domain optical coherence tomography of an active toxoplasma chorioretinal lesion shows disorganization of the retinal layers, retinal thickening, retinal pigment epithelium (RPE) thickening/elevation, and overlying vitreous hyper-reflective dots consistent with overlying vitritis. (b) The same lesion 6 years later showing retinal atrophy, persistent RPE elevation, and resolution of the overlying vitritis. (c) Fluorescein angiogram demonstrates blockage from a small juxtapapillary focus of retinitis with perivascular leakage from the adjacent retinal blood vessels and disc. (d) B-scan ultrasound shows vitreous hyperechogenicity from vitritis and a focal area of chorioretinal elevation corresponding to a toxoplasma chorioretinal lesion.
52.2.2 Fluorescein Angiography or Ultra-Widefield Fluorescein Angiography
May show diffuse or focal retinal vasculitis. The retinal vasculitis is more often a periphlebitis, though arteriolar inflammation is also possible (▶ Fig. 52.3c). There may be a blockage from pigment deposition in the chorioretinal scar and/or a window defect in areas of atrophy. Fluorescein angiography may additionally help in diagnosing CNV associated with the chorioretinal lesion.
52.2.3 Fundus Autofluorescence
Most often notable for hypoautofluorescence in regions of atrophic scarring (▶ Fig. 52.2b).
52.2.4 Ultrasonography
In cases where significant vitritis prohibits adequate examination of the fundus, B-scan ultrasonography may reveal a focal elevation with overlying vitreous hyperechogenicity (▶ Fig. 52.3d) and traction on the retina, which, if severe, may also present as a tractional retinal detachment.
52.3 Critical Work-up
Acquisition of aqueous samples should be considered for toxoplasma polymerase chain reaction (PCR) testing along with serum samples for toxoplasma immunoglobulin G (IgG) and IgM levels for Goldmann–Witmer coefficient analysis, particularly if the diagnosis is unclear. The Sabin–Feldman dye test is used to measure primarily IgG antibodies and titer is considered positive. IgM antibodies, on the other hand, may persist for 1 year or longer, following acute infection. A negative IgM enzyme-linked immunosorbent assay (ELISA) result in an immunologically normal adult almost always excludes recent infection. For congenital toxoplasmosis, IgA ELISA is a more sensitive test for the detection of infection in the fetus and newborn than IgM. Other causes of uveitis such as sarcoidosis, tuberculosis, and syphilis should be ruled out with antitreponemal antibodies, QuantiFERON Gold testing, angiotensin-converting enzyme levels, and a chest X-ray. In cases with chorioretinal lesions, other causes of necrotizing retinitis such as viral retinitis need to be ruled out as well, typically by sending aqueous samples for herpes simplex virus, varicella zoster virus, and cytomegalovirus PCR. In patients with atypical findings such as multiple/bilateral lesions, human immunodeficiency virus testing should be performed.
52.4 Management
52.4.1 Treatment Options
Observation
Small extramacular lesions, which do not threaten vision, may be observed without treatment in immunocompetent patients as the disease is often self-limited.
Concurrent Antivirals
In equivocal cases for toxoplasmosis diagnosis, coverage for potential viral retinitis with oral antivirals (e.g., valacyclovir) is appropriate until aqueous PCR results return.
Antiparasitic Regimen
Lesions within the vascular arcades, those in close proximity to the optic disc, or large lesions >1 disc diameter in size and retinochoroiditis in immunosuppressed patients warrant treatment. There is no clear consensus on the best antiparasitic treatment regimen, but each of the following has been used to treat ocular toxoplasmosis in the United States (▶ Table 52.1).
Pyrimethamine, sulfadiazine, and folinic acid (“triple therapy”).
Trimethoprim/sulfamethoxazole.
Azithromycin.
Atovaquone.
Oral or intravitreal clindamycin.
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