Central Nervous System Infections

Meningitis - Braincoat Baddies

Meningeal inflammation. Triad: fever, headache, nuchal rigidity.

• Bacterial: S. pneumo, N. menin, H. flu (↓vaccine), Listeria (age extremes, immunocomp).
• Viral: Enteroviruses, HSV, VZV.
• TB: M. tb.
• Fungal: C. neoformans (immunocomp).

CSF Analysis - The Decider!

Start["<b>🩺 Suspected Meningitis</b><br><span style='display:block; text-align:left; color:#555'>• Clinical concern</span><span style='display:block; text-align:left; color:#555'>• CNS symptoms</span>"]

LP["<b>🔬 LP and CSF Analysis</b><br><span style='display:block; text-align:left; color:#555'>• Lumbar puncture</span><span style='display:block; text-align:left; color:#555'>• Cell count, labs</span>"]

Bact["<b>💊 Empirical IV Abx</b><br><span style='display:block; text-align:left; color:#555'>• Rocephin plus Vanco</span><span style='display:block; text-align:left; color:#555'>• +/- Ampicillin</span>"]

Viral["<b>👁️ Viral Management</b><br><span style='display:block; text-align:left; color:#555'>• Supportive care</span><span style='display:block; text-align:left; color:#555'>• Acyclovir if HSV</span>"]

TB["<b>💊 TB Treatment</b><br><span style='display:block; text-align:left; color:#555'>• ATT regimen</span><span style='display:block; text-align:left; color:#555'>• Steroid therapy</span>"]

Fungal["<b>💊 Antifungals</b><br><span style='display:block; text-align:left; color:#555'>• AmphoB plus Flucy</span><span style='display:block; text-align:left; color:#555'>• Fungal pattern</span>"]

Start --> LP
LP -->|Bacterial| Bact
LP -->|Viral| Viral
LP -->|TB Pattern| TB
LP -->|Fungal| Fungal

style Start fill:#F7F5FD, stroke:#F0EDFA, stroke-width:1.5px, rx:12, ry:12, color:#6B21A8
style LP fill:#FFF7ED, stroke:#FFEED5, stroke-width:1.5px, rx:12, ry:12, color:#C2410C
style Bact fill:#F1FCF5, stroke:#BEF4D8, stroke-width:1.5px, rx:12, ry:12, color:#166534
style Viral fill:#EEFAFF, stroke:#DAF3FF, stroke-width:1.5px, rx:12, ry:12, color:#0369A1
style TB fill:#F1FCF5, stroke:#BEF4D8, stroke-width:1.5px, rx:12, ry:12, color:#166534
style Fungal fill:#F1FCF5, stroke:#BEF4D8, stroke-width:1.5px, rx:12, ry:12, color:#166534

> ⭐ In bacterial meningitis, CSF glucose is typically **<40** mg/dL or <2/3rd of blood glucose.

📌 **B**acterial = **B**ad CSF (↓Glucose, ↑Protein, ↑PMNs).

## Encephalitis & Myelitis - Brain & Cord Chaos

*   **Encephalitis**: Brain inflammation; fever, headache, altered sensorium, seizures, focal deficits.
*   **Myelitis**: Spinal cord inflammation; weakness, sensory loss, bladder/bowel dysfunction.

**Common Viral Causes & Features:**
*   **Herpes Simplex Virus (HSV-1)**:
    -   Most common cause of sporadic fatal encephalitis.
    -   Affects **temporal lobes** (anosmia, gustatory hallucinations, personality changes).
    -   CSF: Lymphocytic pleocytosis, ↑RBCs.
    -   Rx: Acyclovir **10 mg/kg IV q8h** for **14-21 days**.
    ![MRI T2 FLAIR HSV encephalitis temporal lobe](https://ylbwdadhbcjolwylidja.supabase.co/storage/v1/object/public/notes/L1/Microbiology_Infectious_Diseases_Central_Nervous_System_Infections/d97f1fd0-2523-47ce-ac8e-0cd34930998c.jpg)
*   **Japanese Encephalitis (JE)**:
    -   Arbovirus (Flavivirus); mosquito vector (Culex).
    -   Affects thalamus, basal ganglia, brainstem, cerebellum, spinal cord.
    -   Features: Parkinsonism, acute flaccid paralysis, movement disorders.
    -   📌 Mnemonic: **J**uvenile **E**xtrapyramidal **S**ymptoms (for JE).
*   **Arboviruses (e.g., West Nile Virus)**:
    -   Often cause meningoencephalitis or encephalomyelitis.
    -   Features: Rash, lymphadenopathy, flaccid paralysis (WNV).

> ⭐ CSF PCR is the gold standard for diagnosing HSV encephalitis due to its high sensitivity and specificity, allowing for early and targeted antiviral therapy initiation.

*   **Transverse Myelitis**: Segmental spinal cord inflammation; often post-infectious or autoimmune (e.g., NMO, MS).

## Brain Abscess & Other Focal Infections - Pus Pockets & Peril
*   **Etiology**: Contiguous (sinusitis, otitis, dental); Hematogenous (lung, endocarditis); Trauma/surgery.
*   **Organisms**: *Streptococci* (esp. *S. milleri*), *Staph. aureus*, anaerobes. Polymicrobial common.
*   **Stages (Cerebritis → Abscess)**:
    -   Early (1-2 wks): Inflammation, edema.
    -   Late (2-3 wks): Central necrosis, early capsule.
        > ⭐ Rupture into ventricles: high mortality (>**80%**).
    -   Capsule (>3 wks): Thick, vascular wall.
*   **Imaging (CT/MRI)**: Ring-enhancing lesion, central necrosis (pus), surrounding edema. DWI: Restricted diffusion (key).
![Brain Abscess MRI: Ring Enhancement & Restricted Diffusion](https://ylbwdadhbcjolwylidja.supabase.co/storage/v1/object/public/notes/L1/Microbiology_Infectious_Diseases_Central_Nervous_System_Infections/888c61cc-91f2-4eb0-8322-75dfb928fc81.jpg)


## Specific CNS Infections - Unique Invaders & Ills
*   **Neurocysticercosis** (*Taenia solium* larvae):
    -   Stages: Vesicular (scolex visible, pathognomonic), colloidal vesicular, granular nodular, calcified nodular.
    -   Imaging: CT/MRI shows cysts; "hole-with-dot" sign.
        ![Neurocysticercosis on CT and MRI](https://ylbwdadhbcjolwylidja.supabase.co/storage/v1/object/public/notes/L1/Microbiology_Infectious_Diseases_Central_Nervous_System_Infections/8c327dbc-397f-4eec-9e4b-b1350a33aacc.png)
*   **Rabies** (Lyssavirus):
    -   Phases: Prodromal → acute neurologic (furious/paralytic with hydrophobia, aerophobia) → coma.
    -   Pathognomonic: Negri bodies (intracytoplasmic inclusions in hippocampal neurons).
        ![Rabies: Negri bodies in hippocampus neurons](https://ylbwdadhbcjolwylidja.supabase.co/storage/v1/object/public/notes/L1/Microbiology_Infectious_Diseases_Central_Nervous_System_Infections/bfd2c1fd-6b4c-4944-8db1-62444abd75cb.png)
*   **Prion Diseases** (e.g., Creutzfeldt-Jakob Disease - CJD):
    -   Agent: PrP<sup>Sc</sup> (misfolded prion protein) causing spongiform encephalopathy.
    -   Types: Sporadic (sCJD **~85%**), variant (vCJD - younger, psychiatric symptoms), familial, iatrogenic.
    -   Key: Rapidly progressive dementia, myoclonus.
*   **Progressive Multifocal Leukoencephalopathy (PML)**:
    -   Agent: JC virus (polyomavirus).
    -   Population: Severely immunocompromised (e.g., AIDS with CD4 < **200** cells/μL).
    -   Pathology: Multiple, non-enhancing demyelinating lesions in white matter.
> ⭐ **vCJD**: Pulvinar sign (hyperintensity in posterior thalamus) on MRI is characteristic of variant CJD.


## High‑Yield Points - ⚡ Biggest Takeaways

> * **Bacterial meningitis CSF**: ↑Protein, ↓Glucose, ↑Neutrophils. **Viral meningitis CSF**: Normal glucose, ↑Lymphocytes.
> * **TB meningitis CSF**: Markedly ↓Glucose & ↑Protein, ↑Lymphocytes, **cobweb coagulum**.
> * *S. pneumoniae*: **MCC adult bacterial meningitis**. Neonates: *GBS*, *E. coli*, *Listeria*.
> * **India Ink** for *Cryptococcus neoformans* in **HIV+ meningitis**.
> * **Neurocysticercosis** (*T. solium*): **Ring-enhancing lesions with scolex**.
> * **Herpes Simplex Encephalitis**: **Temporal lobe** involvement; CSF PCR diagnostic.
> * **Brain abscess**: **Ring-enhancing lesions**; *Streptococci*, *Staphylococci*.