Lesson
Connect Latent Infection to Cellular Immune Failure
TE in advanced HIV is usually reactivation of a latent tissue cyst. A new exposure can cause disease, but host control determines whether infection reaches the brain.
- Tissue cyst
- CD4 below 100
- IgG
- Environmental prevention
Do not lose diagnostic context.
Do not lose diagnostic context.
Do not lose diagnostic context.
Document the clinical action.
Place the parasite
Toxoplasma gondii is an intracellular protozoan. Primary infection is often silent and leaves latent cysts in neural and muscle tissue. Severe loss of T-cell control permits replication and necrotizing focal encephalitis.
Define the risk
Risk increases below CD4 100 cells/mm3 and is greatest below 50. Most cases in people with HIV reflect reactivation, so IgG establishes the latent-infection context.
Reduce new acquisition
Avoid raw or undercooked meat and shellfish, wash produce and hands, use gloves with soil, and change cat litter daily with hand protection. Cats can remain in the home and do not need routine testing.
Restore immunity
Effective ART is the durable prevention strategy. Prophylaxis protects the high-risk interval while viral suppression rebuilds cellular control.
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Lesson
Recognize Focal Brain Disease
TE often presents subacutely with headache and focal neurologic dysfunction. Fever can be absent, and imaging is necessary to define lesions, edema, and mass effect.
- Headache
- Focal deficit
- Seizure
- Ring enhancement
- Basal ganglia
Do not lose diagnostic context.
Do not lose diagnostic context.
Do not lose diagnostic context.
Document the clinical action.
Read the examination
Headache, hemiparesis, aphasia, visual change, altered cognition, fever, and seizure can appear over days to weeks. Diffuse encephalitis without a focal lesion is less common but can progress rapidly.
Map the lesions
Contrast CT or MRI typically shows multiple ring-enhancing lesions with surrounding edema, often involving the basal ganglia. A single lesion or atypical distribution remains possible.
Measure mass effect
Document edema, ventricular compression, midline shift, herniation risk, and lumbar-puncture safety before invasive testing.
Keep alternatives visible
Primary CNS lymphoma, tuberculosis, fungal infection, pyogenic abscess, metastasis, Chagas disease, and PML can resemble TE. PML more often affects white matter without enhancement or mass effect outside IRIS.
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Lesson
Build a Response-Aware Diagnosis
Definitive diagnosis needs organism detection, but a measured response to empiric therapy often establishes the working diagnosis when the syndrome, imaging, and IgG agree.
- IgG
- CSF PCR
- Empiric response
- Brain biopsy
- CNS lymphoma
Do not lose diagnostic context.
Do not lose diagnostic context.
Do not lose diagnostic context.
Document the clinical action.
Interpret serology
Most people with TE are IgG positive. A negative IgG makes TE unlikely but does not absolutely exclude it. IgM is usually absent in reactivation, and quantitative titers do not measure CNS disease.
Use CSF selectively
When lumbar puncture is safe, CSF PCR is highly specific but only about 50 percent sensitive and becomes less sensitive after therapy. A negative result cannot rule out TE.
Measure the empiric trial
A compatible syndrome, imaging pattern, IgG, and objective improvement on active therapy support presumptive TE. Record a baseline neurologic examination and reassess within 10 to 14 days.
Escalate nonresponse
Strongly consider brain biopsy with atypical evidence, deterioration during the first week, or no improvement by 10 to 14 days. EBV DNA in CSF raises concern for lymphoma but does not diagnose it alone.
Respect steroid confounding
CNS lymphoma can improve temporarily with corticosteroids. Restrict steroids to a genuine mass-effect indication and interpret subsequent response cautiously.
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Lesson
Protect the High-Risk Interval
Primary TE prophylaxis requires both latent infection and severe immunosuppression. The preferred regimen also covers PCP.
- IgG positive
- CD4 below 100
- TMP-SMX
- G6PD
- Immune recovery
Do not lose diagnostic context.
Do not lose diagnostic context.
Do not lose diagnostic context.
Document the clinical action.
Apply the gate
Start prophylaxis when Toxoplasma IgG is positive and CD4 is below 100 cells/mm3. IgG-negative people need exposure counseling and PCP prevention as indicated, not automatic TE prophylaxis.
Prefer daily TMP-SMX
One double-strength tablet daily is preferred and also prevents PCP. DS three times weekly or SS daily are alternatives when full daily dosing is not tolerated.
Build a complete alternative
Dapsone plus pyrimethamine plus leucovorin or atovaquone with or without pyrimethamine and leucovorin can protect against TE and PCP. Test G6PD before dapsone and give atovaquone with food.
Reject false coverage
Aerosolized pentamidine and dapsone alone do not prevent TE. If used for PCP, another agent must address Toxoplasma risk.
Stop and restart correctly
Stop after CD4 exceeds 200 for more than 3 months with sustained suppression. A 100 to 200 option can be considered after 3 to 6 months of suppression. Restart below 100, or at 100 to 200 with detectable HIV RNA.
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Lesson
Deliver Full CNS Induction
Preferred acute therapy pairs antiparasitic folate-pathway inhibition with protective rescue, or uses full-dose TMP-SMX. Treatment continues long enough to control brain tissue disease.
- Pyrimethamine
- Sulfadiazine
- Leucovorin
- TMP-SMX
- Six weeks
Do not lose diagnostic context.
Do not lose diagnostic context.
Do not lose diagnostic context.
Document the clinical action.
Load pyrimethamine
Give 200 mg once. At 60 kg or less, continue 50 mg daily with sulfadiazine 1,000 mg every 6 hours. Above 60 kg, use pyrimethamine 75 mg daily with sulfadiazine 1,500 mg every 6 hours.
Rescue folate
Give leucovorin 10 to 25 mg daily with pyrimethamine and increase it when marrow toxicity requires. Leucovorin is part of the regimen, not an optional supplement.
Use TMP-SMX as a preferred option
Dose by the TMP component at 5 mg/kg with SMX 25 mg/kg IV or orally twice daily. Use it when pyrimethamine is delayed, unaffordable, inaccessible, or a poorer fit.
Treat the tissue course
Continue acute therapy for at least 6 weeks. Extend treatment when disease is extensive or clinical or radiographic response remains incomplete.
Transition without a gap
Every patient moves directly from induction to chronic maintenance until immune reconstitution is durable.
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Lesson
Preserve Coverage When the First Regimen Fails
An alternative must still treat TE, protect against PCP when needed, reach adequate exposure, and remain safe for marrow, kidney, liver, skin, and blood.
- Clindamycin
- Atovaquone
- G6PD
- Sulfa allergy
- Marrow toxicity
Do not lose diagnostic context.
Do not lose diagnostic context.
Do not lose diagnostic context.
Document the clinical action.
Use the preferred sulfa alternative
Pyrimethamine plus leucovorin plus clindamycin 600 mg every 6 hours treats acute TE when sulfadiazine cannot be used. It does not prevent PCP, so add separate PCP prophylaxis.
Make atovaquone absorb
Atovaquone 1,500 mg twice daily can be used alone or with pyrimethamine and leucovorin or sulfadiazine. Give every dose with a meal or nutritional supplement because absorption varies widely.
Evaluate sulfa allergy
Rapid desensitization can be considered for selected patients. Use atovaquone during the process until therapeutic TMP-SMX dosing is reached.
Protect marrow
Pyrimethamine can cause anemia, neutropenia, and thrombocytopenia. Give leucovorin and monitor CBC closely, commonly at least twice weekly during induction.
Test G6PD before dapsone
Use another agent in G6PD deficiency. Monitor for hemolysis and methemoglobinemia, including symptoms that a routine pulse oximeter may not explain.
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Lesson
Measure Response Before Declaring Failure
Most patients improve within 14 days. Failure is a diagnostic event, not permission to continue unmeasured empiricism.
- Neurologic examination
- Ten to 14 days
- Repeat imaging
- Biopsy
- Adjuncts
Do not lose diagnostic context.
Do not lose diagnostic context.
Do not lose diagnostic context.
Document the clinical action.
Expect a trajectory
About 90 percent of patients improve clinically within 14 days. Follow focal deficits, cognition, fever, seizure, function, lesion size, enhancement, and edema.
Trigger escalation
Clinical or radiologic deterioration in the first week despite adequate exposure, or no clinical improvement by 10 to 14 days, should prompt diagnostic reassessment and strong consideration of brain biopsy.
Use steroids narrowly
Give dexamethasone only for clinically important edema or mass effect and stop as soon as feasible. Steroids can worsen immunosuppression and temporarily improve CNS lymphoma.
Treat seizures, not theoretical seizures
Give antiseizure medication after a TE-associated seizure and continue through acute therapy. Do not use routine prophylaxis without seizure.
Avoid interaction injury
Phenytoin, phenobarbital, carbamazepine, dexamethasone, and selected ARVs interact. Prefer a compatible seizure strategy and verify exposure.
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Lesson
Restore Immunity Without Losing CNS Discipline
ART controls the cause of susceptibility, but timing, interaction management, and inflammatory worsening require a coordinated plan.
- ART timing
- Two to three weeks
- IRIS
- Interactions
- Viral suppression
Do not lose diagnostic context.
Do not lose diagnostic context.
Do not lose diagnostic context.
Document the clinical action.
Use the practical timing
No randomized trial defines an exact date, but ART is generally started within 2 to 3 weeks after TE diagnosis once acute therapy is established.
Map interactions
Review anticonvulsants, dexamethasone, marrow suppressants, renal drugs, and the entire ART regimen. Enzyme inducers can lower ARV exposure and threaten suppression.
Recognize uncommon IRIS
TE IRIS can cause enlarging enhancing lesions, edema, or neurologic worsening after ART. It is uncommon, so verify drug exposure and reconsider the diagnosis before labeling it.
Maintain core therapy
Continue effective ART and anti-Toxoplasma treatment through IRIS when feasible. Use corticosteroids only for clinically significant inflammation and taper promptly.
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Lesson
Suppress Recurrence Until Immunity Returns
Acute therapy controls active lesions but does not remove latent cysts. Maintenance bridges the patient to durable immune reconstitution.
- Secondary prophylaxis
- TMP-SMX
- CD4 above 200
- Six months
- Restart below 200
Do not lose diagnostic context.
Do not lose diagnostic context.
Do not lose diagnostic context.
Document the clinical action.
Begin immediately
Start chronic maintenance after acute treatment. Preferred options are pyrimethamine 25 to 50 mg daily plus sulfadiazine 2,000 to 4,000 mg daily and leucovorin 10 to 25 mg daily, or TMP-SMX DS twice daily.
Preserve PCP coverage
Pyrimethamine, sulfadiazine, and leucovorin and TMP-SMX both protect against PCP. A clindamycin maintenance regimen requires a separate PCP agent.
Stop only after durable recovery
Complete induction, remain asymptomatic, and sustain CD4 above 200 cells/mm3 for more than 6 months in response to ART before stopping.
Restart at the secondary threshold
Restart maintenance if CD4 falls below 200 regardless of HIV RNA. This is stricter than the below-100 threshold for primary prophylaxis because prior TE predicts recurrence.
Use imaging as context
Some specialists obtain MRI before stopping. Residual enhancement can persist despite successful treatment, so imaging supplements rather than replaces clinical and immune evidence.
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Lesson
Build Closed-Loop Neuroinfectious Care
TE succeeds when diagnostic evidence, medication access, response checkpoints, ART, toxicity, and relapse prevention remain connected across care settings.
- Result ownership
- Access
- Neurologic monitoring
- ART
- Maintenance
Do not lose diagnostic context.
Do not lose diagnostic context.
Do not lose diagnostic context.
Document the clinical action.
Own the first 24 hours
Stabilize airway, seizure, and mass effect, obtain contrast imaging, collect safe diagnostic studies, start full-dose therapy, and document the baseline neurologic examination.
Own access and exposure
Secure pyrimethamine or use TMP-SMX without delay, calculate weight-based doses, give leucovorin, pair atovaquone with food, and reconcile every interacting drug.
Own the response date
Schedule neurologic reassessment and repeat imaging, with a defined 10-to-14-day threshold for biopsy or diagnostic escalation.
Own immunity
Start ART in the planned window, confirm viral suppression and CD4 recovery, and distinguish IRIS from failure using evidence.
Own relapse prevention
Deliver maintenance before discharge, monitor toxicity and adherence, and document stopping and restart criteria.
Quick check
Module test
Check the connections.
Each attempt draws 10 questions from the complete 136 question bank.
Each attempt draws a fresh set and rearranges the answer choices.
References
Current clinical foundation.
Lecture material was synthesized with the following contemporary guidance. Verify local policy and current guidance before applying clinical information.