Mastering Acute Encephalitis Guidelines for MRCP Success

Mastering Acute Encephalitis Guidelines for MRCP Success

Acute encephalitis is one of the most critical neurological emergencies you will face in clinical practice and is a consistently high-yield topic in the MRCP exams. It requires swift recognition, rapid investigation, and immediate empirical treatment. For the MRCP candidate, mastering the current UK guidelines ensures you can accurately manage these complex scenarios, securing those crucial marks.

Here is a definitive guide to the essential guidelines for managing acute encephalitis, structured for MRCP revision.

1. Initial Assessment and Resuscitation (The ABCDE Approach)

In an MRCP scenario, the patient with suspected encephalitis is critically ill. Your priority is immediate stabilization.

• Airway & Breathing: Assess for respiratory compromise, often due to depressed consciousness or seizure activity. Intubation may be necessary if the Glasgow Coma Scale (GCS) falls below 8 or there is evidence of aspiration.

• Circulation: Ensure adequate perfusion. Manage hypotension aggressively, as cerebral perfusion pressure is paramount.

• Disability (Neurological Assessment): Perform a rapid assessment of GCS, pupillary response, and focal neurological deficits. Obtain IV access immediately.

• Seizure Management: Seizures are common. If status epilepticus is suspected, initiate emergency anticonvulsant protocols (e.g., Lorazepam, followed by Phenytoin/Levetiracetam).

2. The Hallmark: Clinical Suspicion

Encephalitis is clinically defined by altered mental status (impaired consciousness, personality change, new onset of lethargy/confusion) PLUS two or more of the following:

1. Fever (>38°C)

2. Seizures (new onset)

3. Focal neurological findings (e.g., hemiparesis, dysphasia)

4. CSF pleocytosis (usually lymphocytes dominant)

5. Abnormal neuroimaging consistent with encephalitis (e.g., medial temporal lobe signal changes).

MRCP Tip: Recognizing the classic triad (Fever, Headache, Altered Mental Status) is essential, but remember that focal deficits (especially temporal lobe features like olfactory hallucinations or psychiatric changes) strongly point towards Herpes Simplex Virus (HSV) encephalitis.

3. Immediate Diagnostic Pathway

Once stabilization is underway, the diagnostic workup must be expedited. Time is brain.

A. Neuroimaging: CT vs. MRI

• Immediate CT Scan: Should be performed before lumbar puncture (LP) if there are any signs of raised intracranial pressure (ICP), such as papilledema, GCS < 10, or focal neurological signs (though focal signs can be caused by encephalitis itself, the risk of herniation must be ruled out).

• MRI Scan (The Gold Standard): If safe and available, MRI is far superior to CT. The classic finding in HSV encephalitis is T2/FLAIR hyperintensity in the medial temporal lobes, insula, and cingulate gyrus, often unilaterally or asymmetrically.

B. Lumbar Puncture (LP) and CSF Analysis

LP is crucial for pathogen identification and ruling out other causes (e.g., subarachnoid hemorrhage, bacterial meningitis).

Crucial Tests on CSF:

1. HSV PCR: Essential for the diagnosis of HSV-1 and HSV-2 encephalitis.

2. VZV PCR: For Varicella Zoster Virus.

3. Enterovirus PCR

4. Bacterial Cultures/Gram Stain (to exclude bacterial meningitis)

Don't forget to send serum and CSF samples for paired antibody titres for less common viral and autoimmune causes.

4. Empirical Management: The Acyclovir Mandate

The most important guideline in suspected encephalitis is the immediate initiation of high-dose intravenous Acyclovir (10 mg/kg TDS) as soon as possible, preferably within the first hour of suspicion, even before neuroimaging or CSF results are back.

Key Prescribing Guidelines (MRCP focus):

• Dosage and Route: Acyclovir 10 mg/kg IV every 8 hours.

• Duration: Treatment should be continued for a minimum of 14–21 days.

• Renal Adjustment: Acyclovir is renally excreted. Ensure prompt calculation and adjustment of the dose based on estimated glomerular filtration rate (eGFR) to prevent neurotoxicity.

Adjunctive Therapy:

• Empirical Antibiotics: If bacterial meningitis cannot be excluded (especially if the patient is immunocompromised or critically unstable), empirical broad-spectrum antibiotics (e.g., Ceftriaxone + Vancomycin) should be added to Acyclovir and continued until cultures are negative.

• Corticosteroids: Routine use of steroids is not recommended for suspected viral encephalitis unless there is evidence of coexisting cerebral vasculitis or a specific diagnosis such as acute disseminated encephalomyelitis (ADEM) or certain autoimmune causes.

5. Considering Autoimmune Encephalitis

MRCP often tests candidates on differentiating infectious (viral) from autoimmune causes, especially in cases where HSV PCR is negative or the patient deteriorates despite Acyclovir.

Clues for Autoimmune Encephalitis (AE) (e.g., Anti-NMDAR, Anti-LGI1):

• Insidious onset, rather than acute.

• Prominent psychiatric features, movement disorders (e.g., faciobrachial dystonic seizures in LGI1), or autonomic instability.

• Often associated with an underlying tumor (paraneoplastic syndrome).

If AE is suspected, treatment involves high-dose steroids, intravenous immunoglobulin (IVIg), or plasma exchange (PLEX), followed by second-line immunosuppression (Rituximab, Cyclophosphamide). A formal diagnosis relies on specific antibody testing in serum and CSF.

Summary Checklist for MRCP Encephalitis Scenarios

Mastering these guidelines not only ensures success in your MRCP examinations but, more importantly, equips you with the knowledge to manage this time-critical and devastating condition effectively in your clinical career.