Toxoplasmic Encephalitis

Dr. Xu presented an interesting case of a gentleman without significant past medical history presenting with fevers and headaches, found to have a solitary ring-enhancing brain mass on MRI. He was subsequently diagnosed with toxoplasmic encephalitis after a brain biopsy stained positively for toxoplasmosis. Further evaluation revealed that the patient was HIV+ and had AIDS with a CD4 count <35 data-preserve-html-node="true" with a viral load of 400k. The case prompted several interesting points:

  • The differential for a ring-enhancing mass is affected dramatically by the hosts immunocompetency; thus it is worth screening every individual with a ring enhancing mass for HIV
  • In immunocompetent individuals, consider benign tumors, malignant tumors, or brain abscesses
  • In the immunocompromised, the differential expands considerably and should include toxoplasmic encephalitis, primary CNS lymphoma, and PML

A review on Toxoplasmosis, courtesy of of Dr. Xu


  • Toxoplasmosis gondii is a protozoan parasite acquired through ingestion of oocysts by way of food or environment
  • Primary infection typically consists of a subacute, influenza-like illness prior to entering a quiescent stage
  • Infection can reactivate with Reactivates with severe impairment of host cell-mediated immunity causing severe disease, most commonly as toxoplasmic encephalitis


  • Obligate intracellular protozoan parasite
  • Typically transmitted to humans by eating food/water contaminated by cat feces or blood/organ transplantation
  • Definitive host is cats, where it replicates in the intestines and oocytes shed in feces
  • Humans are an accidental, dead-end host for toxoplasma. Oocytes transform into tachyzoites and encyst in neural and muscle tissue




Clinical Presentation

  • Primary infection
  • Asymptomatic latent infx
  • Reactivation

Most common signs/symptoms:

  • Headache (55%), encephalopathy (52%), fever (46%), seizures (29%)
  • Focal neurologic deficits (69%), hemiparesis (39%), ataxia (30%), cranial nerve palsies (28%)


  • CT or MRI with contrast
    • Ring-enhancing lesions (not always)
    • Most common lesions in basal ganglia, frontal or parietal lobes
  • Toxo IgG (+)

    • Negative IgG does not exclude
  • Presumptive diagnosis:

    • CD4 <100 data-preserve-html-node="true"
    • Neurologic symptoms
    • Focal brain lesion
Ring-enhancing Toxoplasma

Ring-enhancing Toxoplasma


  • Empirically treat with the following drugs that target folate synthesis:
    • Pyrimethamine
    • Sulfadiazine
    • Clindamycin
    • Atovaquone
    • TMP-SMX
  • Few head to head trials
  • Early ART
  • A lack of clinical or radiologic improvement after two weeks of treatment should prompt pursuit of biopsy and workup for other opportunistic disease or non-Hodgkin’s lymphoma

Key Points

  • Screen for HIV in patients presenting with neurologic symptoms + focal brain lesions
  • Empiric treatment for TE should not be delayed if there is high clinical suspicion
  • When pyrimethamine based regimens become cost-prohibitive, alternative regimens, such as atovaquone-sulfadiazine or TMP-SMX can be considered

Thanks so much to Dr. Xu for such an interesting presentation and thorough review!