Mastering Myasthenic Crisis Guidelines for SCE Neurology Success

The Specialty Certificate Examination (SCE) in Neurology demands precise knowledge of both chronic disease management and acute neurological emergencies. Among the most critical and frequently tested acute scenarios is the management of Myasthenic Crisis. As an examiner and specialist, I can attest that candidates often fail to grasp the immediate, structured approach required.

This guide breaks down the essential clinical guidelines for managing Myasthenic Crisis, ensuring you master this high-yield topic for your SCE preparation.

1. Defining and Recognizing Myasthenic Crisis

Myasthenic Crisis is a life-threatening exacerbation of Myasthenia Gravis (MG) characterised by respiratory failure requiring mechanical ventilation. It is a true medical emergency.

Key Recognition Points for SCE:

1. Respiratory Compromise: This is the defining feature. Look for increasing shortness of breath, inability to clear secretions, and declining forced vital capacity (FVC).

2. Bulbar Weakness: Severe dysphagia, difficulty managing secretions, and dysarthria often precede or accompany respiratory failure. This poses a significant aspiration risk.

3. Trigger Identification: Often, the crisis is precipitated by an intercurrent illness (e.g., respiratory tract infection), surgery, or initiation of drugs that worsen neuromuscular blockade (e.g., aminoglycosides, fluoroquinolones, macrolides).

SCE Focus: Never rely solely on subjective breathlessness. Objective measures are mandatory. FVC less than 20 mL/kg or NIF (Negative Inspiratory Force) worse than -30 cm H₂O strongly indicates impending crisis and the need for urgent ITU review.

2. Immediate Triage and Airway Management

The initial steps are identical to any critically ill patient, but with heightened awareness of rapid deterioration.

A. Airway and Breathing

• ITU/HDU Transfer: Immediate consultation with Intensive Care Unit (ITU) is essential.

• Intubation Threshold: Be aggressive. Intubate before complete respiratory collapse. Indications for intubation include:

  • Rapid decline in FVC (trending downwards).

  • FVC < 15 mL/kg (some centres use 20 mL/kg).

  • Increasing work of breathing, accessory muscle use, and rising PaCO₂ (indicating fatigue).

  • Inability to manage secretions or profound bulbar weakness leading to aspiration.

B. Cardiology and Monitoring

• Continuous cardiac monitoring, especially if large doses of cholinesterase inhibitors are given (risk of bradycardia).

C. Identifying and Stopping Cholinesterase Inhibitors (The Critical Guideline Point)

• Temporarily Hold Pyridostigmine: In an acute crisis, anticholinesterase inhibitors (like Pyridostigmine) are typically stopped or significantly reduced. High doses can paradoxically worsen weakness (Cholinergic Crisis), which is clinically indistinguishable from Myasthenic Crisis. Holding the drug eliminates this risk while definitive immunotherapy is initiated. Restarting usually occurs gradually once the patient is stabilised.

3. Definitive Immunomodulatory Therapy Guidelines

Once the patient is stabilised (often in ITU), definitive treatment must be initiated immediately. The two first-line options have equal efficacy but different practical considerations.

SCE Scenario Tip: If a patient has severe cardiovascular disease, poor venous access, or is actively anticoagulated, IVIG is generally the preferred choice over PLEX.

4. Adjunct Management and Post-Crisis Care

A. Corticosteroids

Guidelines Dictate Caution: High-dose steroids (e.g., prednisolone) are crucial for long-term control but should not be initiated immediately during the acute crisis. Steroids can cause a transient worsening of weakness 5-10 days after starting, which is unacceptable in an unstable patient.

• Action: Delay starting or escalating steroids until the patient is clinically stable, intubation risk is past, and PLEX/IVIG effects are kicking in.

B. Identifying and Treating Triggers

• Screen for underlying infections (e.g., chest X-ray, blood cultures, urinalysis).

• Review the patient's entire drug chart and stop any medications known to exacerbate MG (e.g., calcium channel blockers, beta-blockers, certain antibiotics).

C. Long-Term Immunosuppression

Post-crisis, the focus shifts to preventing recurrence. Most patients will require long-term immunosuppression (often starting with steroids, then adding an immunosuppressive sparing agent):

• Azathioprine: Most common first-line agent. Slow onset (6–12 months).

• Mycophenolate Mofetil (MMF): Used as an alternative, particularly if Azathioprine is poorly tolerated.

• Rituximab: Considered for refractory MG, especially MuSK-positive disease.

SCE Takeaway: The Flowchart to Success

For the SCE, you must demonstrate a structured, simultaneous approach:

1. Recognise Crisis: FVC < 20 mL/kg, bulbar involvement, impending respiratory fatigue.

2. Secure Airway: Immediate ITU referral and low threshold for intubation.

3. Stop Pyridostigmine.

4. Treat Definitive: Initiate PLEX or IVIG immediately, considering comorbidities.

5. Identify Triggers: Treat infection and stop exacerbating drugs.

6. Avoid Steroids: Do not start or rapidly increase high-dose steroids in the unstable patient.

Mastering these guidelines will not only ensure you pass the SCE Neurology component but, more importantly, equip you to manage this critical emergency effectively in clinical practice.