Infections, Autoimmune Encephalitis, and Inflammatory Disorders
When the Brain Is Inflamed
Clinical framing
Fever, altered mental status, seizures, focal deficits, and meningeal signs can reflect infection or immune-mediated inflammation of the nervous system.
Urgency
Encephalitis and bacterial meningitis are medical emergencies because delayed treatment can be fatal or cause permanent disability.
Meningitis vs encephalitis
Meningitis
- Headache, fever, neck stiffness
- CSF pleocytosis often prominent
Encephalitis
- Altered behavior or consciousness, seizures, focal deficits
- Brain parenchymal involvement
Altered mental status with seizures and focal deficits is more suggestive of:
Encephalitis affects brain parenchyma and often causes focal cortical dysfunction.
Correct answer: Encephalitis
What is a key diagnostic fluid study in suspected meningitis or encephalitis?
CSF studies are central to diagnosing infectious and inflammatory CNS disease when safe to perform.
Correct answer: lumbar puncture with cerebrospinal fluid analysis
Autoimmune Encephalitis and Mimics
Why it matters
Autoimmune encephalitis can present with psychiatric symptoms, memory loss, seizures, dyskinesias, and autonomic instability, and it may be mistaken for a primary psychiatric illness.
Common clues
Subacute psychiatric symptoms plus seizures and memory loss should raise concern for:
This is a classic red-flag pattern for autoimmune encephalitis.
Correct answer: Autoimmune encephalitis
Why can encephalitis be mistaken for psychiatric illness?
Brain inflammation may produce prominent psychiatric and cognitive symptoms early.
Correct answer: because it can present with behavior and personality changes
Diagnostic Reasoning
Approach to suspected CNS inflammation
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Step 1: Stabilize the patient and assess for airway or seizure risk.
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Step 2: Look for fever, meningeal signs, focal deficits, or new behavioral change.
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Step 3: Obtain urgent imaging when needed before lumbar puncture.
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Step 4: Send CSF, blood tests, and targeted infectious or autoimmune studies.
Which symptom combination most strongly argues against simple primary headache and for CNS inflammation?
Fever and confusion indicate possible CNS infection or inflammation.
Correct answer: Headache with fever and confusion
What is one classic autonomic feature of severe encephalitis?
Autonomic instability can occur in inflammatory brain syndromes, especially severe cases.
Correct answer: blood pressure instability