eMedicine Specialties > Ophthalmology > Infectious Disease

Toxoplasmosis: Differential Diagnoses & Workup

Author: Lihteh Wu, MD, Consulting Surgeon, Department of Ophthalmology, Vitreo-Retinal Section, Instituto De Cirugia Ocular, Costa Rica
Coauthor(s): Teodoro Evans, MD, Retina Fellow, St Michael's Hospital, University of Toronto, Canada; Rafael Alberto García, MD, Chief of Outpatient Services, Department of Ophthalmology, Hospital México of San José, Costa Rica
Contributor Information and Disclosures

Updated: Jul 27, 2007

Differential Diagnoses

Acute Retinal Necrosis
Retinitis, CMV
Endophthalmitis, Fungal
Sarcoidosis
Epimacular Membrane
Tuberculosis
Foreign Body, Intraocular
Uveitis, Anterior, Granulomatous
Glaucoma, Uveitic
Uveitis, Anterior, Nongranulomatous
Ocular Manifestations of HIV
Uveitis, Fuchs Heterochromic
Ocular Manifestations of Syphilis

Other Problems to Be Considered

Toxocariasis
Primary intraocular lymphoma
Pars planitis

Workup

Laboratory Studies

  • Serology
    • The diagnosis is usually based on the clinical appearance of the fundus lesion. Serologic evidence of exposure to Toxoplasma organisms serves as supportive evidence.
    • Serum antitoxoplasma antibody titers can be determined by several techniques, to include the following:
      • Enzyme-linked immunosorbent assay (ELISA)
      • Indirect fluorescent antibody test
      • Indirect hemagglutination test
      • Complement fixation
      • Sabin-Feldman dye test
    • Serologic findings are important in determining whether acute or chronic systemic infection is present. Acute systemic toxoplasmosis has traditionally been diagnosed by seroconversion. Anti-Toxoplasma immunoglobulin G (IgG) titers present a 4-fold increase that peak 6-8 weeks following infection, then decline over the next 2 years, but remain detectable for life. Anti-Toxoplasma IgM appears in the first week of the infection and then declines in the next few months. The presence of anti-Toxoplasma immunoglobulin A (IgA) has also been shown to be detectable in acute infection; however, since the titers can last for more than 1 year, its value in helping to diagnose an acute phase is limited.
    • Antibody titers do not correlate with ocular disease. Antitoxoplasma antibodies may be very low and should be tested in undiluted (1:1) samples if possible. The absence of antibodies rules out the disease; nevertheless, false-negative results do occur.
    • Invasive techniques are usually reserved for difficult cases, such as patients who are immunocompromised. Ocular fluids can demonstrate the presence of intraocular antibody production. Polymerase chain reaction can detect the causative organism.
    • A fluorescent treponemal antibody absorption (FTA-ABS) test should be obtained to rule out syphilis.

Imaging Studies

  • Fluorescein angiography (FA) of active lesions shows hypofluorescence during the early phase of the study, followed by progressive hyperfluorescence secondary to leakage.
  • Indocyanine green
    • Indocyanine green (ICG) of active lesions are mostly hypofluorescent. ICG has imaged hypofluorescent satellite lesions that are not imaged by FA and are not seen during clinical examination.
    • The etiology of such hypofluorescent lesions is unknown but suspected of being a noninfectious, perilesional inflammatory reaction.
  • Optical coherence tomography (OCT) is helpful in identifying potential complications, including epiretinal membrane, cystoid macular edema, vitreoretinal traction, and choroidal neovascularization.
  • Ultrasound is indicated in the presence of ocular media opacities, especially vitreous opacities. The most common findings include intravitreal punctiform echoes, thickening of the posterior hyaloid, partial or total posterior vitreous detachment, and focal retinochoroidal thickening.

Procedures

  • Atypical cases may require either a vitreous sample or an aqueous sample.
  • Polymerase chain reaction is capable of detecting T gondii DNA in either an aqueous sample or a vitreous sample in only one third of patients with ocular toxoplasmosis.
  • Antitoxoplasma IgG or IgA antibodies may be detected in either an aqueous sample or a vitreous sample. A coefficient is calculated by comparing the concentration of anti-Toxoplasma antibody in the eye and the serum, divided by the concentration of gamma globulin in the aqueous to that in the serum. A coefficient of 8 or higher is consistent with active ocular toxoplasmosis.

Histologic Findings

Histopathology is the criterion standard for diagnosis. Tissue diagnosis is impractical and rarely used clinically. Rarely, a retinal biopsy may be required to elucidate the diagnosis in a highly atypical case. In histologic sections, the tachyzoites appear ovoid or crescent shaped. They measure 6-7 µm in length and 2-3 µm in width.

The tachyzoites stain well with both Giemsa stain and Wright stain. Giemsa-stained smears reveal a bluish cytoplasm and a reddish spherical or ovoid nucleus. In the cyst forms, the wall is eosinophilic, argyrophilic, and weakly periodic acid-Schiff (PAS) positive. The cyst may contain anywhere from 50-3000 bradyzoites. The bradyzoites within the cyst are strongly PAS positive. They form intracellularly within vacuoles. The surrounding membrane is produced by the parasite.

An intense inflammatory reaction is present in the retina, the overlying vitreous, and the underlying choroid. The choroid adjacent to the retinal foci usually shows a granulomatous inflammation. The retina is partially necrotic with a well-defined border between necrotic and unaffected retina. After healing, the retina in the area of infection is destroyed, and chorioretinal adhesions are present.

More on Toxoplasmosis

Overview: Toxoplasmosis
Differential Diagnoses & Workup: Toxoplasmosis
Treatment & Medication: Toxoplasmosis
Follow-up: Toxoplasmosis
Multimedia: Toxoplasmosis
References
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Further Reading

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Keywords

Toxoplasma, Toxoplasma gondii, T gondii, congenital toxoplasmosis, acquired toxoplasmosis, toxoplasmosis in immunocompromised host, ocular toxoplasmosis, retinochoroiditis, chorioretinitis, chorioretinal scar, intraocular inflammation, intraocular toxoplasmosis

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Contributor Information and Disclosures

Author

Lihteh Wu, MD, Consulting Surgeon, Department of Ophthalmology, Vitreo-Retinal Section, Instituto De Cirugia Ocular, Costa Rica
Lihteh Wu, MD is a member of the following medical societies: American Academy of Ophthalmology, American Society of Retina Specialists, Association for Research in Vision and Ophthalmology, and Pan-American Association of Ophthalmology
Disclosure: Nothing to disclose.

Coauthor(s)

Teodoro Evans, MD, Retina Fellow, St Michael's Hospital, University of Toronto, Canada
Disclosure: Nothing to disclose.

Rafael Alberto García, MD, Chief of Outpatient Services, Department of Ophthalmology, Hospital México of San José, Costa Rica
Disclosure: Nothing to disclose.

Medical Editor

John D Sheppard Jr, MD, MMSc, Professor of Ophthalmology, Microbiology and Molecular Biology, Clinical Director, Thomas R Lee Center for Ocular Pharmacology, Program Director, Ophthalmology Residency Training, Eastern Virginia Medical School; President, Virginia Eye Consultants
John D Sheppard Jr, MD, MMSc is a member of the following medical societies: American Academy of Ophthalmology, American Society for Microbiology, American Society of Cataract and Refractive Surgery, American Uveitis Society, and Association for Research in Vision and Ophthalmology
Disclosure: Nothing to disclose.

Pharmacy Editor

Simon K Law, MD, PharmD, Assistant Professor of Ophthalmology, Jules Stein Eye Institute; Chief of Section of Ophthalmology Surgical Services, Department of Veterans Affairs Healthcare Center, West Los Angeles
Simon K Law, MD, PharmD is a member of the following medical societies: American Academy of Ophthalmology, American Glaucoma Society, and Association for Research in Vision and Ophthalmology
Disclosure: Nothing to disclose.

Managing Editor

R Christopher Walton, MD, Professor, Director of Uveitis and Ocular Inflammatory Disease Service, Department of Ophthalmology, Assistant Dean for Graduate Medical Education, University of Tennessee College of Medicine; Consulting Staff, Regional Medical Center, Memphis Veterans Affairs Medical Center, St Jude Children's Research Hospital
R Christopher Walton, MD is a member of the following medical societies: American Academy of Ophthalmology, American College of Healthcare Executives, American Uveitis Society, Association for Research in Vision and Ophthalmology, and Retina Society
Disclosure: Nothing to disclose.

CME Editor

Lance L Brown, OD, MD, Ophthalmologist, Affiliated With Freeman Hospital and St John's Hospital, Regional Eye Center, Joplin, Missouri
Disclosure: Nothing to disclose.

Chief Editor

Hampton Roy Sr, MD, Associate Clinical Professor, Department of Ophthalmology, University of Arkansas for Medical Sciences
Hampton Roy Sr, MD is a member of the following medical societies: American Academy of Ophthalmology, American College of Surgeons, and Pan-American Association of Ophthalmology
Disclosure: Nothing to disclose.

 
 
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