Toxoplasmosis

Question 1

Mass-occupying brain lesions in a patient with HIV

Answer 1

• Primary CNS lymphoma
• Syphilitic gummas
• Tuberculosis
• Toxoplasmosis
• Brain abscess

Question 2

Folinic acid

Answer 2

Reduced form of folic acid that does not require reduction by an enzyme for activation

Question 3

Ring-enhancing lesion

Answer 3

Lesion that shows peripheral enhancement with central hypodensity on CT imaging after IV contrast

Unlike other lesions that have uniform/homogeneous enhancement

Question 4

Toxo is seen in AIDS patients with CD5 count less than ___

Answer 4

Toxo is seen in AIDS patients with CD5 count less than 200

Question 5

Transmission of toxoplasmosis

Answer 5

• Ingesting uncooked meat containing cysts
• Ingesting food and water contaminated with oocysts from infected cat feces
• Vertical transmission (TORCH infection)

Question 6

Most common clinical presentation of toxoplasmosis in HIV patients is . . .

Answer 6

. . . encephalitis resulting from multiple brain lesions

Question 7

Diagnostic studies for CNS toxoplasmosis

Answer 7

• MRI showing multiple ring-enhancing lesions (necessary, but nonspecific)
• Serology:
  
  • IgG and IgM titers
    
    • Note: Antibody levels may be very low in AIDS patients , which can result in false negative serologies up to ~22% of the time
• LP and CSF studies:
  
  • Elevated protein
  • T. gondii PCR (moderate sensitivity, high specificity)

Question 8

Interpretation of one vs multiple ring enhancing lesions in an HIV patient with a clinical syndrome suspicious for intracranial mass

Answer 8

One REL: Likely Primary CNS lymphoma

More than one REL: Likely toxoplasmosis

Question 9

When do you resort to brain biopsy for diagnosis of suspected CNS toxoplasmosis?

Answer 9

Only if there is no response after two weeks of empiric treatment for toxo and serologic studies have remained negative

Question 10

Pathology in CNS toxoplasmosis

Answer 10

• Lymphocytic vasculitis
• Microglial nodules
• Astroglial nodules

Question 11

Treatment of CNS toxoplasmosis

Answer 11

• Pyrimethamine for 6 weeks
  
  • with Folinic acid (given its selective activity against dihydrofolate reductase)
  • and with Sulfadiazine (acts synergistically with pyrimethamine)
• If cerebral edema is present, corticosteroids (dexamethasone) should also be given

Question 12

Prophylaxis against toxoplasmosis in HIV patients

Answer 12

Prophylactic bactrim is effective prophylaxis against T. gondii in HIV-infected patients with CD4 counts less than 200

Also: cook meats completely, avoid exposure to cat feces