Ocular Toxoplasmosis

Systemic

Acquired disease in immune competent adults leads to lymphadenopathy in 90% of patients, with fever, malaise, and sore throat in some cases. More severe disease can occur, affecting muscle, skin, brain, heart, kidney, and other organs. Death resulting from toxoplasmosis rarely occurs in the immunocompetent individual. However, in the immunocompromised patient, toxoplasmosis can be a fulminant central nervous system (CNS) disease that rapidly leads to death.

Ocular

Ocular toxoplasmosis can occur with both the congenital and acquired forms of the disease. Acquisition of the disease causes most concern when it occurs during pregnancy. An older article suggests that in the United States, up to six in 1000 women acquire the infection while pregnant, with an approximately 40% risk of transmission of the infection to the fetus. In a report describing the national neonatal screening program for congenital toxoplasmosis in Denmark, 2.1 congenital toxoplasmosis cases were identified per 10,000 newborns. The congenital form of the disease can lead to a wide range of symptoms, but most important to this discussion is that most cases of ocular toxoplasmosis are conjectured to be acquired congenitally, with activation occurring later in life. In the Danish study, 9.6% of those with congenital toxoplasmosis were born with retinal or macular lesions, with 15.6% manifesting these changes at age 3 years. In a European study reported by Koppe and Kloosterman in 1982, 5% of the infants infected would either die or become severely affected by the disease. Furthermore, about 70% of infants with congenital infections will show chorioretinal scars compatible with toxoplasmosis after a follow-up of 16 years, with 1% to 2% suffering severe visual impairment because of this infection. However, evidence suggests that acquired infection may be responsible for the majority of the cases with ocular disease ( Case 15.1 ). In following up the results of an outbreak of systemic toxoplasmosis that occurred in October 1977 in Atlanta, Georgia, in the United States, Wilson and Teutsch reported that one patient in the original group of patients who became ill or had serologic evidence of acute infection showed evidence of ocular disease.

Case 15.1

A 20-year-old woman from Ghana presented with blurry vision in the right eye. Her visual acuity was 20/100 in the right eye and 20/20 in the left eye. Best corrected visual acuity (BVCA) in the right eye was 20/40. The left eye examination was normal, whereas the right eye showed +3 anterior chamber cells, +2 vitreous cells, and trace vitreous haze with a large inferotemporal yellowish chorioretinal lesion, papillitis, and arteriolar sheathing and plaques, also known as Kyrieleis plaques (see Fig. 15.14A ). Fluorescein angiography showed extensive vascular leakage, both arteriolar and venular (see Fig. 15.14B ). The patient received 4 weeks of triple therapy (pyrimethamine, sulfadiazine, and oral prednisone), which was started 48 hours after antimicrobial therapy. Even though the lesion was smaller and more consolidated on follow-up, more vascular plaques and increased haze were noted (see Fig 15.14C ); therefore the triple therapy was continued for another 6 weeks. Four months after the initial presentation, the lesion was completely atrophic, with the Kyrieleis plaques, vitreous haze, papillitis, and vascular leakage all resolved, as shown by fluorescein angiography (see Figs. 15.14D and E ). The patient’s visual acuity improved to 20/25 in the right eye.

A large atrophic scar, frequently in the macula—a result of congenital toxoplasmosis—is usually seen ( Fig. 15.3 ). Although such lesions help in diagnosing an old problem, they do not present the ophthalmologist with a therapeutic problem. Rather, it is the reactivation or the recent acquisition of toxoplasmosis that poses the problem ( Case 15.2 ). In these instances, ocular toxoplasmosis manifests as focal retinitis. The active lesion can vary greatly in size but is usually oval or circular in shape and rarely bullous. Frequently, reactivation sites will be “satellite” lesions next to old atrophic lesions, indicative of previous toxoplasmic infections. During the acute stage of infection, the retina appears thickened, rather than transparent, and is cream colored ( Fig. 15.4 ). Cells are found in the vitreous, particularly overlying the active lesion. Some eyes may have one or two small, old lesions, whereas others may have many, with some lesions being very large and involving several clock-hours of peripheral retina. In some large and particularly recalcitrant lesions, the vitreous haze and cellular reaction can be so profound as to cause decreased vision. In the area surrounding active retinitis, hemorrhage and sheathing of the retinal blood vessels may be seen. Fluorescein angiography of the active lesion demonstrates early blockage with subsequent leakage of the lesion ( Fig. 15.5 ). Indocyanine green (ICG) angiography can show hypofluorescence of both active and inactive lesions. It can also show other areas of choroidal hypofluorescence that do not correspond to the defects seen on fluorescein angiography ( Fig. 15.6 ). Spectralis optical coherence tomography (OCT) has shown that the retinal layers are abnormally hyperreflective at sites of active lesions, with thickening of the posterior hyaloids, which is often focally detached. When the lesions are close to the optic nerve, there can be considerable field loss ; one study reported that 94% of patients with toxoplasmosis had visual field loss as a result of the disease. As mentioned, there is a real risk of disease recurrence, hence the finding of “satellite” lesions. It has been suggested that Toxoplasma cysts would be found in greater numbers near the site of a previous infection, which would seem reasonable. Holland et al. reported that the risk of recurrence was greatest immediately after an episode, particularly within the first few years and that younger patients with ocular toxoplasmosis have a greater chance of recurrence compared with older patients. ^, The longer interval from the first episode was strongly associated with decreased risk of recurrence.

Because the Toxoplasma organism has a propensity for neural tissue, it is important to bear in mind that the lesion classically begins in the retina, and only with ongoing inflammation will it involve not only multiple layers of the retina but also the choroid. Cells in the anterior chamber may also be noted and may appear to be either a granulomatous or nongranulomatous uveitis. In the immunocompetent host, although evidence of old toxoplasmic activity may be present, the disease activates in only one eye at a time in the majority (up to 90%) of patients. With continuing inflammatory disease, the lesion and overlying vitreous will undergo several changes. The vitreous may contract, and posterior vitreal detachment is not uncommon. Further vitreal condensation leads to “scaffolding” of vitreal strands ( Fig. 15.7 ). Roizenblatt et al. described the development of vitreous cylinders in toxoplasmosis as a result of condensation of the collagen fibers. As the lesion becomes less acute, the area of retinal involvement takes on a less bright-yellow appearance, ultimately becoming atrophic, often with pigment heaping around its edges. Pigment clumping, however, does not surround all old lesions and should not be considered a diagnostic cue. The associated retinal disturbance will also begin to resolve. All patients will have visual field defects that correspond to the interruption of the retinal nerve fiber layer. Although unusual, unilateral toxoplasmic anterior optic neuropathy, presenting with sudden painless loss of vision, has been reported.