Diagnostic Tests for Toxoplasma-Induced Seizures
For diagnosing and managing seizures caused by Toxoplasma gondii infection, a comprehensive panel of serologic testing combined with neuroimaging and cerebrospinal fluid analysis is essential, with brain MRI being the most sensitive imaging modality for detecting characteristic lesions. 1
Serologic Testing
Initial Serologic Evaluation
- Toxoplasma-specific IgG and IgM antibodies in serum (primary diagnostic method) 1
- Toxoplasma IgG avidity test (low avidity suggests recent infection) 1
- Toxoplasma IgA and IgE ELISA (especially important for pregnant women >16 weeks gestation) 1
Interpretation Challenges
- Serologic testing interpretation can be complex and confusing 1
- Negative serology does not exclude diagnosis, as cases of Toxoplasma encephalitis have been reported in persons without Toxoplasma-specific IgG antibodies 1
- Consider using a specialized reference laboratory for comprehensive testing and interpretation assistance 1
Neuroimaging Studies
Magnetic Resonance Imaging (MRI)
- MRI is preferred over CT due to higher sensitivity 1
- Look for:
- Multiple, bilateral, ring-enhancing lesions
- Lesions in basal ganglia and cerebral corticomedullary junction
- T2-weighted hyperintensities in cortical white and gray matter 1
Computed Tomography (CT)
- May show multiple, bilateral, ring-enhancing lesions
- Less sensitive than MRI; can be normal despite presence of disease 2
- Should not be used alone to rule out Toxoplasma encephalitis 2
Cerebrospinal Fluid (CSF) Analysis
Standard CSF Tests
- Opening pressure, WBC count with differential, RBC count, protein, glucose 1
- Gram stain and bacterial culture (to rule out other causes) 1
Molecular Testing
Electroencephalography (EEG)
- Important for seizure characterization and monitoring
- May show sporadic single-spike or sharp-wave paroxysms 3
- Useful for monitoring treatment response 3
Definitive Diagnostic Methods
Brain Biopsy
- Gold standard for definitive diagnosis 1, 4
- Consider when:
- Early neurologic deterioration despite empiric treatment
- Failure to respond to anti-Toxoplasma therapy after 10-14 days 1
- Findings may include:
- Leptomeningeal inflammation
- Microglial nodules
- Gliosis
- Toxoplasma cysts 1
Isolation of Organism
- Mouse inoculation or tissue culture of CSF, urine, or blood 1
- Lower sensitivity than serologic and molecular methods
Special Considerations for Immunocompromised Patients
HIV-Infected Patients
- Complete brain MRI should be performed even without focal neurological symptoms 5
- F-fluoro-2-deoxyglucose-positive emission tomography can help distinguish Toxoplasma abscesses from primary CNS lymphoma (though accuracy is not high) 1
- Serum IgG for Toxoplasma gondii is particularly important 1
Congenital Toxoplasmosis Evaluation
- Ophthalmologic, auditory, and neurologic examinations
- Lumbar puncture
- Head imaging (CT or MRI) to check for hydrocephalus or calcifications 1
Monitoring Treatment Response
- Regular EEG to assess normalization of abnormal patterns 3
- Follow-up MRI after 6 weeks of treatment 5
- Weekly complete blood count during daily pyrimethamine treatment 5
- Ophthalmologic evaluations every 2-3 weeks in cases of active chorioretinitis 5
Clinical Pitfalls to Avoid
Do not rule out Toxoplasma encephalitis based on negative serology alone - cases have been reported in patients without detectable antibodies 1
Do not rely solely on CT imaging - MRI is significantly more sensitive for detecting characteristic lesions 2
Consider Toxoplasma in all seizure patients with risk factors - even in immunocompetent individuals with normal CT scans 3, 2
Do not delay empiric treatment while awaiting definitive diagnosis in high-risk patients with compatible clinical and radiological features 1, 6
Remember the association between Toxoplasma and epilepsy - studies show more than two-fold higher Toxoplasma seropositivity in patients with focal and generalized seizures 7