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Toxoplasmosis Retinochoroiditis

URGENT — Uveitis

Symptoms

  • blurred vision: often due to vitreous "fog" or a lesion in the macula
  • floaters: caused by inflammatory cells in the vitreous jelly
  • photophobia and redness: from secondary anterior chamber inflammation
  • pain: typically mild, but can be sharp if eye pressure (IOP) is elevated

Clinical Findings

The classic lesion

  • "headlight in the fog": a fluffy white focal retinitis obscured by overlying vitritis
  • satellite lesion: a new white lesion appearing directly adjacent to an old, pigmented scar
  • unilateral: usually affects one eye at a time in immunocompetent patients

Associated signs

  • vitritis: intense inflammatory debris directly over the active area
  • kyrieleis arteritis: yellowish plaques along the retinal arteries near the inflammation
  • vasculitis: perivascular sheathing (inflammation of the vessels)
  • neuroretinitis: optic disc swelling with a "macular star" of hard exudates

Immunocompromised variant

  • punctate outer retinal toxoplasmosis: deep, multiple lesions with very little vitreous haze

Etiology

Pathogen

  • toxoplasma gondii: an intracellular protozoan; cats are the definitive host

Transmission

  • congenital: passed from mother to fetus during a primary pregnancy infection
  • acquired: ingestion of oocysts (undercooked meat, contaminated water, or cat feces)

Reactivation

  • cysts remain dormant in old scars and can rupture later in life, especially during pregnancy or immunosuppression

Red Flags

  • vision-threatening location: any lesion in the macula or near the optic nerve requires immediate systemic therapy
  • "headlight in fog": severe vitritis that hides the fundus makes it hard to rule out other infections (like ARN)
  • hiv/immunosuppression: lesions may be bilateral, multifocal, or rapidly progressive; requires aggressive workup
  • bone marrow suppression: pyrimethamine treatment can drop blood counts; must monitor CBC

Investigations

Lab work

  • serum antibody: IgG (indicates past exposure) or IgM (indicates recent infection)
  • rule of thumb: a negative titer in an immunocompetent patient makes toxo very unlikely

Ocular sampling

  • pcr: testing the aqueous or vitreous fluid for T. gondii DNA; highly specific for atypical cases

Systemic screening

  • rule outs: HIV, syphilis (RPR), and TB (QuantiFERON) before starting high-dose steroids

Treatment

Observation

  • small, peripheral lesions in healthy patients may resolve without treatment

First-line (triple therapy)

  • pyrimethamine: (load then daily) + Folinic Acid (to protect bone marrow)
  • sulfadiazine: or TMP-SMX (Bactrim DS) as a more accessible alternative

Adjuvants

  • prednisone: to reduce inflammatory damage; must be used alongside antibiotics
  • intravitreal: clindamycin/dexamethasone injections for patients who can't take oral meds

Associated issues

  • topical: steroids and cycloplegics for anterior segment "spillover" inflammation

Clinical Pearl

Most common cause of infectious retinochoroiditis globally. Classic presentation: active white fluffy lesion adjacent to an old pigmented scar ("satellite lesion"). PCR of aqueous/vitreous most sensitive for atypical cases.

Differential Diagnosis

  • • cmv retinitis (usually "pizza-pie" appearance, minimal vitritis, seen in advanced AIDS)
  • • acute retinal necrosis (arn) (rapidly spreading, peripheral, viral etiology)
  • • syphilitic retinitis (the "great imitator"; always check RPR/FTA-ABS)
  • • cat-scratch disease (bartonella; look for neuroretinitis and history of cat scratches)

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