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Encephalitis
Inflammation of the brain parenchyma, often viral in origin, presenting with altered mental status, seizures, and focal neurologic deficits. Can be life-threatening.
Viral Encephalitis (Most Common)
HSV-1 Encephalitis
- Temporal lobe involvement on MRI; may cause personality changes, hallucinations.
- Rapid progression, high mortality if untreated.
Clinical Presentation:
- Fever, headache, altered mental status
- Focal neurologic signs (aphasia, hemiparesis)
- Seizures
- Behavioral changes, hallucinations
- Photophobia, nausea/vomiting possible
Labs & Imaging:
- CSF: Lymphocytic pleocytosis, elevated protein, normal glucose
- PCR for HSV in CSF = gold standard
- MRI: Temporal lobe hyperintensities
- EEG: Periodic sharp waves over temporal regions
Treatment:
- IV Acyclovir ASAP — don’t wait for PCR confirmation
- Supportive care, seizure management
Arboviral Encephalitis
- West Nile, Eastern Equine, Western Equine, St. Louis, etc.
- Often mosquito-borne, more common in summer/fall, or endemic/travel areas
Clinical Presentation:
- Similar to HSV (fever, AMS, seizures), but also:
- Tremors, myoclonus
- Flaccid paralysis (esp. in West Nile)
- May progress slowly or wax/wane
Diagnosis:
- Serology (IgM) in serum or CSF
- CSF: Lymphocytic pleocytosis, elevated protein
- MRI often normal or non-specific
Treatment:
- Supportive only (no antivirals)
- Prevention via mosquito control
Meningitis
Acute Bacterial Meningitis
- Most serious and rapidly progressing form
- Streptococcus pneumoniae and Neisseria meningitidis are most common in adults
- Group B Strep, E. coli, and Listeria are common in neonates
Clinical Presentation:
- Fever
- Headache
- Nuchal rigidity
- Photophobia
- Altered mental status
- Petechial rash (meningococcemia)
- Seizures or cranial nerve palsies
CSF Findings:
- Elevated opening pressure
- Elevated protein
- Decreased glucose
- Predominantly neutrophilic pleocytosis
Diagnosis:
- Blood cultures and lumbar puncture
- CT head first if signs of increased ICP (papilledema, focal deficits)
- Gram stain and culture of CSF
Empiric Treatment:
- Ceftriaxone + Vancomycin
- Add Ampicillin if Listeria coverage needed (neonates, elderly, immunocompromised)
- Dexamethasone before or with first antibiotic dose to reduce neurologic complications
Viral (Aseptic) Meningitis
- Most common cause overall, often self-limiting
- Enteroviruses (e.g., coxsackie, echovirus) most common
- HSV-2, VZV, HIV also possible causes
Clinical Presentation:
- Fever
- Headache
- Photophobia
- Mild nuchal rigidity
- Mental status typically preserved
CSF Findings:
- Normal or mildly elevated opening pressure
- Normal or mildly elevated protein
- Normal glucose
- Lymphocytic pleocytosis
Treatment:
- Supportive care
- Consider acyclovir for suspected HSV or VZV
Fungal Meningitis
- Seen in immunocompromised patients, especially HIV/AIDS
- Cryptococcus neoformans is the most common
Clinical Presentation:
- Subacute onset
- Headache
- Fever
- Malaise
- Cranial nerve deficits
CSF Findings:
- Elevated opening pressure
- Lymphocytic pleocytosis
- Low glucose
- Elevated protein
Diagnosis:
- India ink stain
- Cryptococcal antigen (CrAg)
- Fungal culture
Treatment:
- Amphotericin B + Flucytosine, then fluconazole maintenance
Tuberculous Meningitis
- Reactivation of latent TB, especially in high-risk or immunocompromised patients
- Often involves the base of the brain
Clinical Presentation:
- Gradual onset
- Fever
- Night sweats
- Weight loss
- Cranial nerve deficits
CSF Findings:
- Very high protein
- Very low glucose
- Lymphocytic pleocytosis
- May require large volume CSF sample for AFB stain/culture
Imaging:
- MRI with basilar meningeal enhancement
Treatment:
- RIPE therapy + steroids
- Rifampin
- Isoniazid
- Pyrazinamide
- Ethambutol
