# Clinical Cases: Neuroinfectious Diseases

## Case 1: Herpes Simplex Encephalitis

### Patient Demographics
- **Age:** 34 years
- **Sex:** Female
- **Occupation:** Elementary school teacher

### Chief Complaint
"She's been confused and had a seizure this morning."

### History of Present Illness
The patient was brought to the emergency department by her husband after experiencing a generalized tonic-clonic seizure at home this morning. Over the past 4 days, she has had progressively worsening headache, fever (up to 39.2C), and fatigue. Two days ago, she began having difficulty finding words and seemed confused, not recognizing her own children. Yesterday, her husband noticed she was behaving strangely - "acting like a different person" with inappropriate comments and irritability. She had no prior history of seizures. No recent travel, no immunocompromising conditions.

### Neurological Examination Findings

**Vital Signs:**
- Temperature: 39.0C (102.2F)
- HR: 102, BP: 138/85, RR: 18

**Mental Status Examination:**
- GCS: 13 (E3V4M6)
- Disoriented to time and place
- Impaired attention - cannot recite months backward
- **Expressive aphasia** - word-finding difficulty, paraphasic errors
- Short-term memory severely impaired
- Intermittent agitation and perseveration

**Cranial Nerves:**
- Pupils 3mm, equal, reactive
- Visual fields intact to confrontation
- No facial asymmetry
- Intact gag reflex

**Motor Examination:**
- 5/5 strength bilateral upper and lower extremities
- Normal tone

**Sensory Examination:**
- Intact to light touch

**Reflexes:**
- 2+ symmetric
- Plantar responses flexor bilaterally

**Coordination:**
- Unable to assess reliably due to encephalopathy

### Key Clinical Features Suggesting HSV Encephalitis
1. **Acute/subacute encephalopathy** with altered mental status
2. **Fever** - present in most cases
3. **Seizures** - common, especially with temporal lobe involvement
4. **Behavioral changes** - personality change, psychiatric symptoms
5. **Aphasia** - temporal lobe involvement
6. **Focal neurological findings** - temporal lobe predilection

### Neuro Workup

**Laboratory Studies:**
- WBC: 12,500 (mild leukocytosis)
- CMP: Normal
- Coagulation: Normal

**Lumbar Puncture:**
- Opening pressure: 22 cm H2O (mildly elevated)
- WBC: 185 cells/uL (95% lymphocytes) - **lymphocytic pleocytosis**
- RBC: 450 cells/uL - **suggests hemorrhagic component**
- Protein: 85 mg/dL (elevated)
- Glucose: 58 mg/dL (normal, serum glucose 95)
- **HSV PCR: POSITIVE for HSV-1** (results in 24-48 hours)
- Gram stain: Negative
- Bacterial culture: No growth

**MRI Brain with Contrast:**
- **T2/FLAIR hyperintensity in bilateral temporal lobes (left > right)**
- Involvement of insular cortex and orbitofrontal regions
- Possible petechial hemorrhage on susceptibility-weighted imaging
- No enhancement yet (early)
- **Characteristic finding:** Medial temporal lobe involvement with relative sparing of basal ganglia

**EEG:**
- Periodic lateralized epileptiform discharges (PLEDs) over left temporal region
- Background slowing

### Diagnosis
**Herpes Simplex Virus Encephalitis (HSV-1)**

### Management

**Immediate Treatment (started empirically before HSV PCR results):**
1. **Intravenous Acyclovir 10 mg/kg every 8 hours**
   - Started immediately upon clinical suspicion
   - Do NOT wait for PCR confirmation
   - Duration: 14-21 days
   - Renal dosing adjustment if needed
2. **Seizure prophylaxis/treatment:**
   - Levetiracetam 1000 mg IV load, then 500 mg BID
3. **Supportive care:**
   - ICU admission for monitoring
   - Fever control
   - IV fluids
   - Aspiration precautions

**Monitoring:**
- Neurological checks every 2 hours
- Repeat imaging if clinical deterioration
- Monitor for increased intracranial pressure
- Renal function monitoring (acyclovir nephrotoxicity)

**Follow-up:**
- Repeat LP near end of treatment to document viral clearance (controversial)
- MRI at completion of therapy
- Neuropsychological evaluation for cognitive sequelae
- Long-term seizure management if epilepsy develops

**Prognosis:**
- Mortality with treatment: ~15-20%
- Mortality without treatment: >70%
- Common sequelae: Memory impairment (Kluver-Bucy syndrome if bilateral temporal), personality changes, seizures, aphasia
- Early treatment significantly improves outcomes

### Clinical Image
![Herpes Simplex Encephalitis MRI](case_01_image.jpg)

**Image Description:** MRI showing T2/FLAIR hyperintensity involving the temporal lobes bilaterally, characteristic of herpes simplex encephalitis. The medial temporal structures including hippocampus and insular cortex are preferentially affected.

**Attribution:** Image from Wikimedia Commons. Licensed under CC BY-SA 3.0. Source: https://commons.wikimedia.org/wiki/File:Herpes_simplex_encephalitis.jpg

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## Case 2: Brain Abscess

### Patient Demographics
- **Age:** 52 years
- **Sex:** Male
- **Occupation:** Construction worker

### Chief Complaint
"Severe headache and weakness on my right side for 5 days."

### History of Present Illness
The patient presents with a 2-week history of progressively worsening headache, initially generalized but now localized to the left frontotemporal region. Over the past 5 days, he has developed weakness of his right arm and leg and has had difficulty speaking clearly. He has had low-grade fevers (up to 38.3C) and night sweats for 3 weeks. He has also noticed nausea and has vomited twice today. His wife reports he has been "not himself" with slowed thinking. His medical history includes poorly controlled type 2 diabetes (HbA1c 9.8%) and he had a dental abscess requiring extraction 6 weeks ago.

### Neurological Examination Findings

**Vital Signs:**
- Temperature: 37.9C (100.2F)
- HR: 88, BP: 148/92, RR: 16

**Mental Status Examination:**
- Alert but slow to respond
- Oriented to person only
- Impaired concentration
- Mild expressive difficulties

**Cranial Nerves:**
- Pupils equal and reactive
- **Papilledema on fundoscopy** - blurred disc margins bilaterally
- Right central facial droop (forehead spared)

**Motor Examination:**
- Right upper extremity: 3/5 (deltoid, biceps, triceps, grip)
- Right lower extremity: 4/5 (hip flexion, knee extension, ankle dorsiflexion)
- Left side: 5/5 throughout
- Increased tone right side

**Sensory Examination:**
- Decreased sensation right arm and leg to light touch

**Reflexes:**
- Right side: 3+ biceps, triceps, brachioradialis, patellar, Achilles
- Left side: 2+
- **Right Babinski: Extensor** (upgoing toe)
- Left plantar: Flexor

**Coordination:**
- Cannot assess right side due to weakness
- Left side: Normal finger-to-nose

**Gait:**
- Unable to ambulate safely - right hemiparetic gait

### Risk Factors Identified
1. **Diabetes mellitus** - poorly controlled (immunocompromised state)
2. **Recent dental infection** - potential source of hematogenous spread
3. **Contiguous spread risk factors:** None identified

### Neuro Workup

**Laboratory Studies:**
- WBC: 15,200 with left shift (80% neutrophils)
- ESR: 78 mm/hr (elevated)
- CRP: 145 mg/L (elevated)
- Blood glucose: 285 mg/dL
- Blood cultures: Drawn (pending)
- HbA1c: 9.8%

**CT Head without Contrast (initial):**
- Left frontal hypodense lesion with surrounding edema
- Mass effect with midline shift 6mm to right
- Effacement of left lateral ventricle

**MRI Brain with Contrast:**
- **3.5 cm ring-enhancing lesion** in left frontal lobe
- **Smooth, thin-walled enhancing rim** (thinner on ventricular side)
- Central T2 hyperintensity (necrotic center)
- Extensive surrounding vasogenic edema
- **Restricted diffusion on DWI/ADC** - bright on DWI, dark on ADC
  - Key distinguishing feature from necrotic tumor
- Midline shift with subfalcine herniation

**Lumbar Puncture:**
- **CONTRAINDICATED** due to significant mass effect and herniation risk

**CT Chest/Abdomen/Pelvis:**
- No evidence of pulmonary abscess or other source

**Echocardiogram:**
- No vegetations (ruling out endocarditis)

### Diagnosis
**Brain Abscess** - likely odontogenic source (post-dental extraction)
- Most likely organisms: Streptococcus species (viridans group), anaerobes (Bacteroides, Peptostreptococcus, Fusobacterium)

### Management

**Immediate Medical Treatment:**
1. **Empiric IV Antibiotics (started immediately):**
   - **Ceftriaxone 2g IV q12h** (covers streptococci, gram-negatives)
   - **Metronidazole 500mg IV q8h** (covers anaerobes)
   - **Vancomycin 15-20 mg/kg IV q8-12h** (covers MRSA - added given immunocompromised)
   - Total duration: 6-8 weeks IV antibiotics

2. **Cerebral Edema Management:**
   - **Dexamethasone 10mg IV load, then 4mg q6h**
   - Head of bed elevated 30 degrees
   - Avoid hypercarbia

3. **Seizure Prophylaxis:**
   - Levetiracetam 500mg IV BID (supratentorial lesion)

4. **Glucose Control:**
   - Insulin infusion to target glucose 140-180 mg/dL

**Surgical Treatment:**
- **Neurosurgery consulted emergently**
- **Stereotactic aspiration performed** - both diagnostic and therapeutic
  - Purulent material obtained
  - Gram stain: Gram-positive cocci in chains, gram-negative rods
  - Culture: Streptococcus intermedius, Fusobacterium nucleatum
  - Antibiotics narrowed based on culture/sensitivities

**Indications for Surgery Met:**
- Abscess >2.5 cm diameter
- Significant mass effect
- Neurological deterioration
- Accessible location

**Follow-up:**
- Serial MRI every 2 weeks to monitor resolution
- Continue antibiotics until abscess cavity resolved or stable residual
- Long-term antiepileptic drugs if seizures occur
- Dental evaluation and treatment of any remaining dental disease

**Prognosis:**
- Mortality: 5-15% with modern treatment
- Factors associated with poor outcome: Poor GCS at presentation, rapid progression, intraventricular rupture, multiple abscesses
- Most patients have good functional recovery with early treatment

### Clinical Image
![Brain Abscess MRI](case_02_image.jpg)

**Image Description:** Contrast-enhanced MRI showing a ring-enhancing brain abscess with smooth, thin walls and surrounding vasogenic edema. The central cavity shows restricted diffusion, distinguishing abscess from necrotic tumor.

**Attribution:** Image from Wikimedia Commons. Licensed under CC BY-SA 3.0. Source: https://commons.wikimedia.org/wiki/File:Contrast-enhanced_MRI_of_a_brain_abscess.jpg

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## Key Teaching Points

### Herpes Simplex Encephalitis
1. Most common cause of sporadic viral encephalitis
2. **Temporal lobe predilection** - behavioral changes, aphasia, seizures
3. **Start acyclovir empirically** - do not wait for PCR results
4. CSF shows lymphocytic pleocytosis, may have RBCs
5. MRI more sensitive than CT - T2/FLAIR hyperintensity in temporal lobes
6. Early treatment dramatically improves survival

### Brain Abscess
1. Classic triad: Headache (most common), fever (~50%), focal deficit (~50%)
2. **Ring enhancement with restricted diffusion** distinguishes from tumor
3. Common sources: Dental, sinusitis, otitis, endocarditis, hematogenous
4. Empiric antibiotics: Cover streptococci, anaerobes, +/- staph
5. Surgery for abscess >2.5 cm or significant mass effect
6. LP contraindicated with mass effect
7. Duration: 6-8 weeks IV antibiotics