Myasthenia Gravis & Myasthenic Crisis — Mastery Guide

🧠 Myasthenia Gravis & Myasthenic Crisis — Mastery Guide

Diagnosis, Triggers, Respiratory Support, and ICU Care in All Settings

📘 Part of the Neuromuscular Emergencies in the ICU Series

Prepared for Dr. Amir Fadhel – Specialist in Anesthesiology and Critical Care
🗓️ Created on: 05/06/2025

📖 About This Guide

Developed in collaboration with Sophia (ChatGPT-4o), this teaching guide continues the legacy of the ABG, Mechanical Ventilation, ARDS, Guillain-Barré, and Sedation Mastery series. It provides a detailed and practical approach to Myasthenia Gravis and Myasthenic Crisis, highlighting:

Early recognition of neuromuscular fatigue
Triggers and red flags for crisis
Crisis differentiation (myasthenic vs cholinergic)
Ventilator management and medication strategies
And essential adaptations for low-resource ICUs

This guide aims to empower clinicians with structured, actionable tools to improve care delivery in both advanced and rural critical care settings.

📚 Table of Contents

1️⃣ What Is Myasthenia Gravis?
2️⃣ Clinical Subtypes & Typical Presentations
3️⃣ Diagnosis of Myasthenia Gravis
▫️ Diagnostic Pearls
▫️ Lambert-Eaton Differential
4️⃣ Classification & Severity Staging
5️⃣ Pharmacologic Therapy in MG
6️⃣ What Is Myasthenic Crisis?
7️⃣ Triggers & Risk Factors of Crisis
8️⃣ Recognizing Crisis: Red Flags & Respiratory Monitoring
9️⃣ Myasthenic vs. Cholinergic Crisis
🔟 Ventilatory Support in Crisis
1️⃣1️⃣ Immunotherapy During Crisis
1️⃣2️⃣ Perioperative Planning in MG
1️⃣3️⃣ Managing MG in Limited-Resource Settings
1️⃣4️⃣ Long-Term Care & Relapse Prevention
1️⃣5️⃣ Pocket Summary, Mnemonics & Clinical Pearls
1️⃣6️⃣ Advanced MCQ Bank — 15 Clinical Scenarios with Explanations
1️⃣7️⃣ Final Words & Mastery Series Access

1️⃣ What Is Myasthenia Gravis?

🧠 Definition

Myasthenia Gravis (MG) is a chronic autoimmune neuromuscular junction (NMJ) disorder characterized by fluctuating, fatigable weakness of skeletal muscles. The condition is caused by autoantibodies targeting key components of the postsynaptic NMJ, most commonly the acetylcholine receptor (AChR).

🎯 Hallmark: Weakness worsens with repeated use and improves with rest.

🧬 Pathophysiology — The NMJ Under Attack

In MG, antibodies interfere with neuromuscular transmission by:

Blocking the AChR
Cross-linking and internalizing receptors
Activating complement-mediated destruction of the motor endplate

🧪 Primary Antibodies in MG

Antibody	Target	Prevalence	Features
Anti-AChR	Acetylcholine receptor	~80% of cases	Classic generalized MG
Anti-MuSK	Muscle-specific kinase	5–8%	Bulbar-predominant, often more severe
Anti-LRP4	Agrin receptor complex	1–5%	Milder or ocular MG
Seronegative	—	Up to 10%	Diagnosed clinically + EMG/response to therapy

🧠 MuSK-positive MG tends to have more severe bulbar symptoms, weaker response to acetylcholinesterase inhibitors, and a greater likelihood of requiring ICU care.

🧪 Neuromuscular Junction Recap — Normal vs. MG

Normal NMJ	Myasthenia Gravis NMJ
Nerve releases ACh → binds to AChRs → muscle contracts	Antibodies reduce AChRs → ↓ signal → weakness

👁️ Classic Clinical Features

Muscle Group	Symptoms
Ocular	Ptosis, diplopia — often asymmetric
Bulbar	Dysphagia, dysarthria, nasal speech
Facial	Weakness, “myasthenic snarl,” reduced smile
Neck	Head drop
Limb (proximal)	Difficulty combing hair, climbing stairs
Respiratory	Dyspnea, orthopnea, “air hunger” in crisis

🧠 Sensation and deep tendon reflexes are preserved — an important distinguishing feature from GBS and motor neuron diseases.

📈 Fatigability — The Key Symptom

Myasthenia is not a fixed weakness. Instead:

Muscles weaken with repeated or prolonged use
Symptoms improve with rest
Morning strength > evening strength

💡 Key Clinical Teaching Pearls

✅ MG is postsynaptic — no sensory symptoms, no reflex changes
✅ Bulbar involvement is a major predictor of respiratory failure
✅ Ptosis that improves with ice pack test supports diagnosis
✅ No fasciculations, no atrophy — differentiates from ALS

2️⃣ Clinical Subtypes & Typical Presentations

🧬 Why Subtypes Matter

Recognizing the subtype of MG helps predict:

Disease severity
Crisis risk
Response to therapy
And even anesthetic safety during surgery

🧠 Primary Clinical Subtypes of MG

Subtype	Key Features
Ocular MG	Symptoms limited to ptosis + diplopia; normal limb/bulbar strength
Generalized MG	Involves ocular + bulbar + limb + respiratory muscles
MuSK-positive MG	Severe bulbar/respiratory weakness, less ocular; often female, steroid-sensitive
Thymoma-associated MG	Any type + thymic mass; may have paraneoplastic symptoms
Seronegative MG	Negative for AChR/MuSK, but positive EMG findings; milder, variable response

👁️ 1. Ocular Myasthenia Gravis

Isolated ptosis or diplopia
Often asymmetric
May remain ocular or progress to generalized within 1–2 years

🔍 Tip: Look for lid fatigue or Cogan’s lid twitch when patient looks from down to up.

💪 2. Generalized Myasthenia Gravis

Most common type in clinical practice
Includes proximal limb, bulbar, and respiratory muscles
Weakness worsens with exertion, especially later in the day

🧠 Think “choking on soup, slurred speech, short of breath after walking.”

👩‍⚕️ 3. MuSK-positive MG

Muscle-specific kinase antibody
Severe bulbar, neck, and respiratory weakness
Often female
Weak response to pyridostigmine
Responds well to steroids and rituximab

🔴 Red Flag: Rapid deterioration, risk of crisis, often requiring ICU.

🧫 4. Thymoma-associated MG

May present with any phenotype, but has a higher likelihood of generalization
CT chest should be done in all newly diagnosed MG patients
Thymectomy often improves disease and prevents progression
Paraneoplastic syndromes (e.g., red cell aplasia) may coexist

❓ 5. Seronegative MG

No detectable antibodies
Diagnosis via repetitive nerve stimulation, SFEMG, and clinical response
Often milder, but can still lead to crisis

🩺 MGFA Classification (Preview)

In the next section, we will classify patients using standardized scales like the Myasthenia Gravis Foundation of America (MGFA) system — used for tracking severity and planning treatment.

💡 Teaching Pearls

✅ Not all MG starts in the eyes — MuSK-positive cases skip ocular involvement
✅ Thymoma can occur in young or old — don’t miss it
✅ Any patient with neck weakness, slurred speech, or dyspnea may be heading toward myasthenic crisis
✅ Always re-check ptosis or dysphagia at the end of the day — that’s when MG shows itself

3️⃣ Diagnosis of Myasthenia Gravis

🧭 Diagnostic Approach Overview

Diagnosing MG is clinical first, then supported by:

Serologic testing (antibodies)
Neurophysiology (repetitive nerve stimulation or SFEMG)
Response to cholinergic drugs
Imaging (to assess for thymoma)

🎯 In suspected MG, always ask:
“Are symptoms fatigable, fluctuating, and improving with rest?”

🩺 Step-by-Step Diagnostic Strategy

1️⃣ Bedside Tests

Test	How It Works	Interpretation
Ice pack test	Apply ice to ptotic eyelid for 2–5 mins	Improvement = MG (sensitive for ocular MG)
Rest test	Let ptotic lid rest → then reassess	Transient improvement = suspect MG
Cogan’s lid twitch	Look down → then up → lid briefly overshoots	Suggestive of ocular MG

2️⃣ Serologic Testing

Antibody	Detected in	Notes
Anti-AChR	~80–85% of generalized MG	High specificity
Anti-MuSK	~5–8%, more in bulbar MG	May be AChR-negative
Anti-LRP4	1–5%	Often milder, sometimes isolated ocular

🧪 If all three are negative → seronegative MG — proceed to neurophysiology.

3️⃣ Neurophysiological Tests

Test	Key Use	Notes
Repetitive nerve stimulation (RNS)	↓ in CMAP amplitude with repeated stimuli	Specific, but less sensitive in mild MG
Single-fiber EMG (SFEMG)	Measures jitter between muscle fibers	Most sensitive test for MG

🔬 SFEMG is the gold standard — but may not be widely available.

4️⃣ Pharmacologic Test (Optional)

🧪 Edrophonium (Tensilon) Test

Short-acting acetylcholinesterase inhibitor
Rapid improvement in ptosis or diplopia = positive test

⚠️ Caution: Can cause bradycardia or cholinergic symptoms. Always have atropine ready.

This test is now rarely used due to side effects and availability of better diagnostics.

5️⃣ Chest Imaging for Thymoma

Why?	MG is associated with thymic hyperplasia and thymoma
What to order?	CT chest with contrast
When?	In all newly diagnosed MG patients

🧠 Thymoma can occur at any age and may be asymptomatic. Don’t skip imaging.

🔍 Example Diagnostic Flow

Clinical suspicion
Ice pack test positive
Anti-AChR antibody positive
Chest CT: thymic mass
Diagnosis: generalized MG, thymoma-associated

💡 Diagnostic Pearls

✅ Diagnosis is clinical + confirmatory
✅ Don’t wait for full paralysis to test
✅ SFEMG is most sensitive
✅ Always screen for thymoma, even if asymptomatic
✅ MG can mimic many things — but it’s the fatigability that gives it away

🔍 Differential Diagnosis Spotlight — Lambert-Eaton Myasthenic Syndrome (LEMS)

Though clinically similar to MG, Lambert-Eaton Myasthenic Syndrome (LEMS) is a presynaptic NMJ disorder that must be considered, particularly in older patients, smokers, or those with autonomic symptoms and proximal leg weakness.

Feature	Myasthenia Gravis (MG)	Lambert-Eaton Syndrome (LEMS)
NMJ Defect Site	Postsynaptic (ACh receptors)	Presynaptic (voltage-gated Ca²⁺ channels)
Antibodies	Anti-AChR, Anti-MuSK	Anti-VGCC (P/Q-type)
Onset	Ocular/bulbar first	Proximal lower limb weakness > ocular
Reflexes	Normal	Reduced or absent → improve after exercise
Autonomic Symptoms	Rare	Common (dry mouth, erectile dysfunction)
Facial/Bulbar Signs	Common	Rare
EMG	Decremental response	Incremental response with high-frequency RNS
Associated Malignancy	Thymoma (esp. in younger patients)	Small Cell Lung Cancer (50–60% of cases)

🧠 Clues to LEMS:

Muscle strength improves with use

Absent reflexes reappear after exertion

Unexplained autonomic symptoms

🩺 Chest imaging is essential in suspected LEMS due to strong paraneoplastic association.

4️⃣ Classification & Severity Staging

📊 Why Classification Matters

Accurate classification allows clinicians to:

Stratify patients for therapy intensity
Predict risk of myasthenic crisis
Track disease progression over time
Decide on ICU admission or preoperative precautions

🧱 The Two Most Common Systems

We’ll focus on:

MGFA Classification – Used globally in clinical trials and ICU protocols
Osserman Classification – Historical but still referenced

📘 MGFA Clinical Classification

(Myasthenia Gravis Foundation of America)

Class	Description
Class I	Ocular MG only (ptosis, diplopia)
Class IIa	Mild generalized: limb/trunk (not bulbar)
Class IIb	Mild generalized: includes bulbar or respiratory symptoms
Class IIIa	Moderate limb/trunk without bulbar involvement
Class IIIb	Moderate with bulbar or respiratory involvement
Class IVa	Severe generalized MG without bulbar symptoms
Class IVb	Severe with bulbar or respiratory weakness
Class V	Defined myasthenic crisis (requires intubation or non-invasive ventilation)

💡 Class IIb, IIIb, IVb should trigger early ICU consult — especially in MuSK-positive MG.

📕 Osserman Classification

(Used historically and in older literature)

Type	Clinical Features
Type I	Ocular MG
Type IIa	Mild generalized; slow progression
Type IIb	Moderate to severe generalized (often bulbar/respiratory)
Type III	Acute fulminant onset with early respiratory crisis
Type IV	Late-onset, often associated with thymoma

🧠 Type III is closest to modern Class V — represents a direct crisis presentation.

🛏️ ICU Risk Stratification from MGFA

MGFA Class	ICU Risk?	Notes
I	No	Ocular symptoms only
IIa	Low	Monitor outpatient or in ward
IIb	Moderate	Bulbar = pre-crisis → watch for SBC/NIF
IIIb & IVb	High	Admit to ICU or step-down with q4h respiratory checks
V	Very High	Crisis – intubation/NIV, close autonomic monitoring

🔍 Functional Testing to Pair With Classification

Test	Why It Matters
Single Breath Count (SBC)	SBC < 15 = impending crisis
NIF / VC	NIF < –30 cmH₂O, VC < 20 mL/kg → ICU
Bedside swallowing	Wet voice, cough, pooling saliva → early intubation

💡 Classification Pearls

✅ Any class with bulbar involvement = crisis risk
✅ Class V = crisis by definition (regardless of strength)
✅ Always monitor respiratory metrics + bulbar signs together
✅ Class progression may be triggered by infection, surgery, or drug exposure

5️⃣ Pharmacologic Therapy in Myasthenia Gravis

Balancing Cholinergic Tone, Immunity, and ICU Safety

💊 Therapeutic Overview

Treatment in MG aims to:

Improve neuromuscular transmission
Suppress autoimmunity
Avoid crisis-inducing drugs
Prepare for flares or perioperative stress

There are two pillars:

Symptomatic therapy (acetylcholinesterase inhibitors)
Disease-modifying therapy (steroids, immunosuppressants, biologics)

1️⃣ Acetylcholinesterase Inhibitors (AChEi)

Drug	Route	Dose Range	Notes
Pyridostigmine	Oral/IV	30–60 mg q4–6h (max 360 mg/day)	First-line for symptom control
Neostigmine	IV (rare)	0.5–2.5 mg IV in monitored setting	Used only when PO not tolerated

🔹 Mechanism: Inhibits acetylcholinesterase → ↑ ACh at NMJ
🔹 Onset: 30–60 min; Duration: ~3–4 hours
🔹 Do not use as monotherapy in moderate/severe cases or crisis risk

⚠️ Excessive dosing may precipitate cholinergic crisis

🧠 Side Effects of AChEi — Remember “DUMBELS”

Cholinergic Toxicity
Diarrhea
Urination
Miosis
Bronchorrhea
Emesis
Lacrimation
Salivation

💡 If patient worsens after increasing pyridostigmine, always consider cholinergic crisis.

2️⃣ Corticosteroids

Drug	Dose	Notes
Prednisone	Start low (10–20 mg/day), titrate up	May transiently worsen symptoms in first week

🔹 Begin after stabilizing airway and symptoms
🔹 Response usually seen in 2–4 weeks
🔹 Avoid high initial doses in unstable or bulbar MG

🧠 In crisis-prone MG, start steroids after or alongside IVIG/PLEX to prevent worsening

3️⃣ Steroid-Sparing Immunosuppressants

Drug	Onset of Action	Notes
Azathioprine	3–6 months	TPMT testing before start; risk of leukopenia
Mycophenolate mofetil	3–6 months	GI side effects common
Cyclosporine / Tacrolimus	Weeks–months	Monitor renal function and BP

💡 Use in patients needing long-term control with steroid toxicity concerns.

4️⃣ Monoclonal & Advanced Biologics

Drug	Target	Use Case
Rituximab	CD20 B cells	Especially in MuSK-positive MG
Eculizumab	Complement C5	Refractory AChR-positive MG

🎯 These agents are expensive but lifesaving in resistant MG or severe MuSK forms.

🚫 Drugs to Avoid in MG — Critical in ICU and OR

Category	Examples
Antibiotics	Aminoglycosides, fluoroquinolones, macrolides
Cardiac meds	Beta-blockers, verapamil, procainamide
NM blockers	Suxamethonium (prolonged), non-depolarizing (exaggerated)
Others	Magnesium sulfate, lithium, statins (rarely)

⚠️ Even topical beta-blockers (e.g., timolol eye drops) can trigger decompensation!

💡 Teaching Pearls

✅ Always start pyridostigmine low and slow — avoid overdose
✅ Don’t start steroids alone in crisis-prone patients
✅ Watch for transient worsening in first week of steroids
✅ Monitor for cholinergic symptoms — especially in ICU
✅ Ask about drug exposures in all sudden worsening cases

6️⃣ What Is Myasthenic Crisis?

🆘 Definition

Myasthenic Crisis is a life-threatening exacerbation of Myasthenia Gravis, defined by:

🔺 Respiratory failure requiring mechanical ventilation
🔺 Often accompanied by bulbar dysfunction — dysphagia, dysarthria, aspiration risk

It represents MGFA Class V, and may be the first presentation in some patients.

📊 Epidemiology & Relevance

Occurs in 15–20% of MG patients at some point
First presenting feature in ~20% of crisis cases
Often requires ICU admission, ventilatory support, and immunomodulation

🔁 Pathophysiology of Crisis

Mechanism	Result
Autoantibody surge or unopposed immune flare	↓ AChR function → NMJ failure
↓ Neuromuscular transmission	Progressive diaphragm + bulbar fatigue
Aspiration or infection	Worsens respiratory load → crisis spiral

🧠 Crisis is often precipitated, not spontaneous — find the trigger.

🔺 Clinical Picture of Crisis

Domain	Presentation
Bulbar	Dysphagia, dysphonia, pooling secretions, nasal speech
Respiratory	Dyspnea, paradoxical breathing, weak cough, orthopnea
Facial/Neck	Inability to lift head, weak smile, facial droop
Autonomic (late)	Hypoventilation, CO₂ retention, drowsiness

🧠 How It Differs From Usual MG Worsening

Worsening ptosis or fatigue ≠ crisis
Bulbar signs + respiratory compromise = pre-crisis
CO₂ retention or SBC <15 = enter ICU, prepare to intubate

💔 The Emotional Weight

This is the moment where speech falters, breath shortens, and the clinician must act with decisiveness and clarity.
But with preparation and vigilance, crisis is survivable.

💡 Clinical Insight

✅ Crisis may develop over hours or days — don't wait for cyanosis
✅ Bulbar signs precede ventilatory collapse
✅ Infections, pregnancy, surgery, or steroid initiation may all precipitate crisis
✅ Time is diaphragm — secure airway before fatigue becomes arrest

7️⃣ Triggers and Risk Factors of Myasthenic Crisis

🧨 Why It Matters

Myasthenic crisis is rarely spontaneous.
It is almost always triggered — by infections, medications, interventions, or even emotional stress.

Knowing what precipitates a crisis allows us to:

Prevent ICU admissions
Prepare perioperatively
Adjust medications safely
Intervene early in resource-limited settings

🔎 Common Crisis Triggers — Categorized

Category	Examples
Infections	Respiratory (pneumonia), urinary tract infections, sepsis
Medications	Aminoglycosides, fluoroquinolones, beta-blockers, magnesium
Surgery / Anesthesia	Intubation/extubation failure, NMB use, sedative overdose
Pregnancy / Postpartum	Immune fluctuation, underdosed therapy
Emotional / Physical stress	Sleep deprivation, psychological trauma, exertion
Steroid initiation	Rapid dose escalation may transiently worsen MG
Non-adherence	Skipping AChEi or immunosuppressants
Vaccinations	Rarely in uncontrolled MG; always balance benefits vs risk

🚩 ICU-Important Drug Triggers to Remember

Unsafe Drug	Why It Triggers Crisis
Aminoglycosides	Blocks presynaptic ACh release
Fluoroquinolones	Disrupts NMJ transmission
Beta-blockers	↓ muscle strength, masks tachycardia
Magnesium sulfate	Direct NMJ blocker — beware in preeclampsia!
Neuromuscular blockers	Profound sensitivity → prolonged paralysis

💊 Even local anesthetics, sedatives, and opioids must be titrated cautiously.

💡 Red Flags Before Crisis

✅ Sudden onset dysphagia
✅ Pooling saliva, gurgling voice
✅ Sleepy appearance + CO₂ retention
✅ SBC <15, VC <20 mL/kg, NIF <–30 cmH₂O
✅ New pneumonia in a previously stable MG patient

🛡️ Crisis Prevention Checklist

✅ Review all medications before prescribing
✅ Give stress-dose steroids during surgery if patient is already on chronic steroids
✅ Educate patients on early symptoms of bulbar fatigue
✅ Ensure compliance with immunosuppressants
✅ Preoperative neurology consult for all MG patients undergoing surgery

🧠 Clinical Insight

Crisis begins in the throat, not in the lungs.
If your patient can't swallow or speak clearly — it's not “just fatigue.”
It’s a storm on the horizon.

8️⃣ Recognizing Crisis — Red Flags & Respiratory Monitoring

🆘 When Fatigue Becomes Failure

In Myasthenic Crisis, respiratory failure is not sudden —
It’s a slow unraveling:
A weakening cough, a softening voice, a quiet struggle with each breath...

Your job is to see it before it strikes.

🔎 Early Red Flags — The Unseen Warnings

System	Red Flag
Bulbar	Nasal voice, dysphagia, gurgling speech, drooling
Respiratory	Dyspnea, orthopnea, paradoxical breathing, accessory muscle use
Neurologic	Inability to hold head up, facial diplegia, shallow smile
Cognitive	Sleepiness, CO₂ retention signs (e.g., confusion, “air hunger,” agitation)

🧠 The diaphragm fails last — but by then, the airway may already be lost.

🫁 Bedside Respiratory Monitoring Tools

These are your stethoscope, your shield, your compass:

Tool	Normal	Threshold to Act
Vital Capacity (VC)	60–70 mL/kg	< 20 mL/kg = prepare to intubate
Negative Inspiratory Force (NIF)	–60 to –90 cmH₂O	> –30 cmH₂O = danger
Single Breath Count (SBC)	> 25	< 15 = critical zone
SpO₂ / ABG	Normal early in crisis	Rising CO₂ or falling pH = late warning

🔺 If two of these are breached — call for ICU support and prepare for intubation.

🗣️ Clinical Voice Signs — Soft Indicators of Collapse

Weak, nasal voice
Counting words before breath
Unable to finish a sentence without pausing
Speech becomes wet or gurgling

🧪 The “20–30–15 Rule” for Crisis

Use this simple triad to remember critical thresholds:

VC < 20 mL/kg
NIF > –30 cmH₂O
SBC < 15

✅ Any one of these = urgent reassessment
✅ Any two = intubation very likely needed

🛏️ ICU Admission Criteria for MG

Admit to ICU if…
Rapidly worsening limb or neck weakness
Bulbar symptoms with weak cough/swallow
VC < 20 mL/kg or SBC < 15
Worsening ABG (↑ PaCO₂, ↓ pH)
Suspected pneumonia or aspiration

🕯️ Final Insight — Recognizing the Silent Decline

Respiratory failure in Myasthenic Crisis is often insidious rather than abrupt. Hypoventilation may precede hypoxia, especially in patients with intact lungs. Thus, oxygen saturation may remain deceptively normal, while CO₂ accumulates silently.

Clinical vigilance must outweigh reliance on late ABG changes.

Do not wait for cyanosis, bradycardia, or altered mental status.

Timely recognition of:

Bulbar weakness (gurgling speech, inability to handle secretions)
Progressive single breath count decline
Loss of neck or facial strength
And objective respiratory thresholds (VC < 20 mL/kg, NIF > –30 cmH₂O)

…should prompt immediate airway planning and ICU escalation.

In neuromuscular respiratory failure, delays in intubation carry significant mortality.
Airway protection and pre-emptive ventilatory support remain the cornerstone of safe crisis management.

9️⃣ Myasthenic vs. Cholinergic Crisis

Two crises. One deadly mistake.

⚖️ Why This Distinction Matters

Both crises can present with:

Respiratory failure
Bulbar weakness
Diffuse muscle weakness
And even a history of pyridostigmine use

But their treatments are opposites:

| If you give more AChEi in cholinergic crisis… | You worsen it. 🛑
| If you stop AChEi in myasthenic crisis… | You worsen it. 🛑

🎯 Correct recognition = lifesaving. Wrong assumption = fatal delay.

🔬 Core Pathophysiology

Crisis Type	Mechanism
Myasthenic Crisis	Too little ACh at NMJ → antibody-mediated blockade or severe fatigue
Cholinergic Crisis	Too much ACh → overstimulation → receptor desensitization and depolarization block

🔍 Side-by-Side Clinical Comparison

Feature	Myasthenic Crisis	Cholinergic Crisis
Muscle weakness	Flaccid, fatigable	Flaccid
Pupils	Normal or dilated	Miosis (pinpoint pupils)
Secretions	Normal or dry	Salivation, lacrimation, bronchorrhea
GI symptoms	None	Diarrhea, cramping, nausea, vomiting
Bradycardia	Less common	Prominent
Fasciculations	Rare	May be present early
Tensilon test	Improves weakness	Worsens weakness (caution!)
Response to atropine	No effect	Reverses muscarinic symptoms

🧪 Role of the Tensilon (Edrophonium) Test

Caution: Use only in monitored settings

Action	Interpretation
Weakness improves → Myasthenic crisis
Weakness worsens + ↑ secretions → Cholinergic crisis

🛑 Tensilon is rarely used today due to risk of bradycardia, bronchospasm — especially in unclear cases.

💉 Management Approach Based on Crisis Type

Action	Myasthenic Crisis	Cholinergic Crisis
AChEi (e.g., pyridostigmine)	Continue or restart	Stop immediately
Atropine	Not used	Used (for muscarinic signs)
IVIG / Plasmapheresis	Indicated	Not helpful
Steroids	Yes, after stabilization	No effect
Ventilatory Support	Often needed	Often needed

🧠 Teaching Pearls

✅ Cholinergic crisis is rare but should be suspected in overmedicated or unstable patients
✅ Pupil exam and secretions are the bedside giveaways
✅ Bronchorrhea + bradycardia + diarrhea = Think cholinergic
✅ If unsure, hold AChEi and provide supportive care while reassessing

🔟 Ventilatory Support in Myasthenic Crisis

When the breath weakens, the machine must protect it.

🫁 Principles of Ventilatory Management

In Myasthenic Crisis, respiratory failure is due to pump failure, not lung pathology. The primary goal is to:

Support gas exchange (esp. CO₂ elimination)
Protect the airway from aspiration
Allow time for immunotherapy and recovery

📌 When to Intubate — Not Too Early, Never Too Late

Indication	Action
SBC < 15, VC < 20 mL/kg, NIF > –30	Intubate or prepare immediately
Bulbar symptoms (secretions, dysphagia)	Preemptive airway protection
CO₂ retention on ABG	Intubate, avoid hypoventilation-related arrest
GCS < 8 or altered mental status	Immediate intubation

✅ Noninvasive ventilation (NIV) may be attempted only in alert, cooperative patients without aspiration risk — but this is rare.

🔧 Initial Ventilator Settings (Invasive)

Mode: Volume Assist-Control (AC-VC) or Pressure Assist-Control (AC-PC)
Goal: Minimize fatigue, optimize comfort

Parameter	Initial Setting
Tidal Volume	6–8 mL/kg IBW
RR	12–16 breaths/min
PEEP	5 cmH₂O (increase only if atelectasis)
FiO₂	Start 100%, titrate to SpO₂ ≥ 92%
Trigger	Flow-based; sensitive but avoid auto-trigger
Sedation	Light-moderate (propofol or fentanyl)

🧠 Avoid paralytics unless absolutely necessary. Neuromuscular monitoring is unreliable in MG.

🔁 Monitoring During Mechanical Ventilation

Daily weaning trials (when VC, NIF recover)
Monitor for aspiration pneumonia
Watch for dysautonomia, especially in ICU-acquired weakness
Track ABG trend: early respiratory acidosis is common

📤 Weaning & Extubation Criteria

Weaning Parameter	Target
SBC	≥ 20
VC	≥ 20–25 mL/kg
NIF	≤ –30 cmH₂O
Secretions	Minimal, managed independently
Bulbar function	Intact swallow, strong cough
Mental status	Alert and cooperative

✅ Always perform a spontaneous breathing trial (SBT) before extubation.
✅ Extubation in MG must be carefully coordinated with neurology and respiratory therapy.

💡 Extubation Tips in Resource-Limited Settings

Use SBC or handheld VC devices if no spirometry available
Monitor work of breathing, fatigue signs at bedside
Ensure suction equipment is ready — bulbar function is the weak link
Keep re-intubation supplies nearby

1️⃣1️⃣ Immunotherapy During Myasthenic Crisis

Targeting the cause, not just the consequence.

🎯 Therapeutic Goals

Immunotherapy in crisis serves to:

Reduce autoantibody burden
Stabilize neuromuscular transmission
Prevent recurrence and long-term progression

This is where neurology meets intensive care — a multidisciplinary, often life-saving intersection.

💉 First-Line Options in Crisis

Therapy	Mechanism	Onset
IVIG	Neutralizes pathogenic antibodies	3–5 days
Plasmapheresis (PLEX)	Physically removes circulating autoantibodies	2–4 days
High-dose steroids	Immunosuppression (delayed effect)	1–2 weeks

🔀 IVIG vs. Plasmapheresis: Choosing Wisely

Consideration	IVIG	Plasmapheresis
Speed of effect	Similar (3–5 days)	Similar (2–4 days)
Vascular access needed	Peripheral line	Central line or large bore access
Volume shift risk	Less	Higher (hypotension risk)
Contraindications	Renal failure, hyperviscosity	Sepsis, unstable hemodynamics
Ease in low-resource ICU	Easier to administer	Requires trained personnel + filter
Cost and availability	Expensive, but simpler logistics	May be cheaper but infrastructure-heavy

🧠 In limited-resource settings, IVIG is often preferred despite its cost due to accessibility and safety.

📦 Steroid Use in Crisis — A Double-Edged Sword

Issue	Clinical Implication
Delayed benefit	Takes ~7–10 days to kick in
Steroid-induced worsening	May transiently worsen weakness in first 5 days
Tapering plan	Begin with high dose, taper once stable
Stress-dose coverage	Required perioperatively or during crisis

Typical Dose:

IV Methylprednisolone 1–2 mg/kg/day or
Oral Prednisone 60–100 mg/day (can be initiated if stable)

💡 Some centers begin steroids after IVIG/PLEX to avoid early worsening.

🧠 Immunosuppressants: For Long-Term Control

Agent	Notes
Azathioprine	Slow onset (2–3 months), check TPMT levels
Mycophenolate	Well tolerated, also slow to act
Cyclosporine / Tacrolimus	Used selectively; nephrotoxic
Rituximab	Anti-CD20; useful in MuSK+ MG

🔁 These are not useful acutely, but should be planned post-crisis to prevent recurrence.

💡 Clinical Tips

Always check renal function and hydration before IVIG
Consider thrombosis prophylaxis in IVIG patients
For PLEX: adjust other medications (e.g., antibiotics, anticonvulsants) since they may be removed with plasma

1️⃣2️⃣ Perioperative Planning in Myasthenia Gravis

Where anesthesia, muscle relaxants, and stress collide.

⚠️ Why Perioperative Management is Critical

Myasthenic patients are exquisitely sensitive to:

Sedatives and anesthetic agents
Neuromuscular blocking drugs
Surgical stress and fasting
Aspiration risk from bulbar weakness

Even a minor procedure may tip them into respiratory failure or crisis if poorly planned.

🧠 Preoperative Evaluation

Domain	Checklist
Disease severity	Assess current muscle strength, bulbar signs, respiratory status
Medications	Continue pyridostigmine until day of surgery
Immunotherapy	Optimize with IVIG/PLEX if recent crisis
Pulmonary tests	VC, NIF, SBC if high-risk procedure planned
Anesthesia consult	Essential: avoid long-acting NMBAs and plan for post-op care

💉 Anesthesia Considerations

✅ Safe Options

Regional anesthesia whenever possible (e.g., spinal, epidural, nerve blocks)
Short-acting agents: propofol, sevoflurane, remifentanil
Sugammadex if rocuronium is used

❌ Risky or Contraindicated

Agent	Concern
Succinylcholine	Resistant or prolonged blockade
Non-depolarizing NMBAs (e.g., vecuronium)	Exaggerated response, prolonged recovery
Benzodiazepines	Exacerbate muscle weakness
Opioids (high dose)	Respiratory depression, especially in crisis

🧪 Always titrate muscle relaxants carefully, with neuromuscular monitoring if available.

🚨 Intraoperative Red Flags

Prolonged paralysis after small NMBA dose
Hypoventilation despite apparent adequate reversal
Increased salivation, gurgling, weak cough → bulbar decompensation

🛌 Postoperative Planning

Consideration	Best Practice
ICU bed availability	For moderate/severe MG or bulbar involvement
Resume AChEi early	Avoid prolonged NMJ dysfunction post-op
Ventilatory support	Keep NIV or invasive ventilation option ready
Pain control	Avoid oversedation (use regional techniques)

💡 In resource-limited ICUs, close bedside monitoring and early detection of bulbar signs may replace advanced monitors.

✍️ Case Tip from the Field

A 52-year-old female with mild MG underwent laparoscopic cholecystectomy under GA. Post-op, she could not raise her head or speak clearly. She was extubated without VC/NIF check.
Result? Emergency reintubation within 1 hour.

Lesson: Never underestimate MG — always assess extubation readiness and bulbar function before removing the tube.

1️⃣3️⃣ Managing MG in Limited-Resource Settings

Because care must never be a privilege.

🏥 Common Limitations

No access to IVIG or plasmapheresis
Delayed antibody testing
No neuromuscular monitoring (VC, NIF)
No ICU ventilator or ABG machine
Limited specialist access (neuro/immunology)

💡 Practical ICU Strategies

Challenge	Alternative or Workaround
No antibody test	Use clinical triad: fluctuating weakness, ocular/bulbar signs, normal reflexes
No VC/NIF measurement	Use Single Breath Count (SBC): count to 20 = safe; <15 = watch; <10 = intubate
No IVIG or PLEX	Try high-dose steroids (0.75–1 mg/kg/day) + supportive ventilation
No invasive ventilator	Use BiPAP/NIV with close monitoring (target RR < 24, pCO₂ < 45)
No pulse oximeter or ABG	Watch accessory muscle use, speech pattern, exhaustion
No neurologist available	Use structured protocol, monitor daily swallow, voice, SBC, neck flexion

🌾 Rural Tips from the Field

🔹 Split IVIG between patients if urgently needed — give 0.4 g/kg x 3 days instead of 5 days
🔹 Use bedside suction & positioning to protect airway
🔹 Preload patients with pyridostigmine before major transfers
🔹 Train nursing staff to recognize silent deterioration (weak cough, whisper voice, pooling saliva)

🧠 "MG doesn't demand fancy machines — it demands vigilance, timing, and calm decisions.”

1️⃣4️⃣ Long-Term Care & Relapse Prevention

Myasthenia is lifelong — but so is mastery.

🌿 Goals of Long-Term Management

Achieve and maintain clinical remission
Minimize medication side effects
Prevent future myasthenic crises
Promote quality of life and functional independence

💊 Maintenance Therapies

Therapy	Role
Pyridostigmine	Mainstay for symptom control
Steroids	Immunosuppressive bridge and backbone
Azathioprine	First-line steroid-sparing agent
Mycophenolate mofetil	Alternative in intolerant or refractory patients
Rituximab	Especially effective in MuSK+ MG
Cyclosporine / Tacrolimus	Used in select cases

🧠 Taper steroids slowly once other immunosuppressants are active (often takes months).

🧬 Monitoring and Follow-Up

Regular neurologic assessments (strength, bulbar function)
Spirometry or SBC in those with respiratory involvement
Blood work for immunosuppressant toxicity (CBC, LFTs, renal function)
Screen for osteoporosis, infections, adrenal suppression if on chronic steroids

🔁 When to Refer or Escalate

Trigger	Action
Frequent exacerbations	Review meds, check compliance, re-evaluate plan
Intolerable side effects	Switch immunosuppressant
Crisis recurrence	Consider PLEX/IVIG maintenance
MuSK+, AChR–, or refractory MG	Consider Rituximab or trials

👶 Special Populations

Pregnancy:
MG can worsen during or after pregnancy.
- Steroids and IVIG are safe
- Avoid mycophenolate, methotrexate, rituximab
- Neonatal MG may occur from transplacental antibodies
Elderly:
More prone to cholinergic toxicity, polypharmacy, and thymoma

🛡️ Lifestyle & Patient Empowerment

Encourage routine, not exertion — avoid excessive fatigue
Vaccinate (e.g., flu, pneumococcal), but avoid live vaccines in immunosuppressed
Educate patient and family about:
- Medication compliance
- Recognizing early relapse signs
- When to seek ICU-level care

💬 Quote from a long-term patient:

“I learned that MG is not a prison — it's a partnership between my body and my discipline.”

1️⃣5️⃣ Pocket Summary, Mnemonics & Clinical Pearls

The whole journey, compressed for action.

📋 Pocket Summary — Myasthenia Gravis & Myasthenic Crisis

Domain	Key Points
Cause	Autoantibodies (AChR, MuSK, LRP4) impair postsynaptic NMJ transmission
Symptoms	Fluctuating weakness, fatigability, ptosis, dysphagia, dyspnea
Preserved	Sensation, reflexes (differentiates from GBS and ALS)
Crisis Definition	Respiratory failure needing ventilation ± bulbar dysfunction
SBC Threshold	< 15 → danger; < 10 → intubate
NIF / VC	NIF > –30 cmH₂O, VC < 20 mL/kg = ICU alert
Cholinergic Signs	Miosis, bradycardia, salivation, diarrhea → Stop AChEi, give atropine
Treatment	Pyridostigmine, steroids, immunosuppressants, IVIG or PLEX in crisis
Ventilation	AC/VC or AC/PC preferred; avoid paralytics
Perioperative Risk	High; avoid NMBA, continue AChEi, extubate cautiously
Differential	LEMS: improves with activity, reflexes depressed, autonomic symptoms

🧠 High-Yield Mnemonics

🎯 “WEAK” — Classic Myasthenia Presentation

Weakness (fluctuating)
Eyes (ptosis, diplopia)
Areflexia absent (but preserved)
Key muscles: bulbar, respiratory, proximal limbs

🧪 “Too Much ACh = SLUDGE” (Cholinergic Crisis)

Salivation
Lacrimation
Urination
Diarrhea
Gastro upset
Emesis

💡 “20–30–15 Rule” — When to Intubate

VC < 20 mL/kg
NIF > –30 cmH₂O
SBC < 15

➕ Any two → prepare airway
➕ All three → intubate

🧬 “AChR = MG. VGCC = LEMS”

ACh receptor = Myasthenia
Voltage-gated calcium channel = Lambert-Eaton

🛡️ “AVOID” — Drugs That Can Precipitate Crisis

Aminoglycosides
Verapamil / beta-blockers
Opioids (high dose)
Inhibitors (e.g., magnesium)
D-penicillamine

💎 Clinical Pearls

✅ Ocular-only MG may evolve to generalized within 2 years
✅ MuSK+ patients often need ICU earlier and respond poorly to pyridostigmine
✅ Cholinergic crisis is rare but deadly — always review dosing
✅ Pre-op planning with anesthesia and neurology saves lives
✅ If in doubt during a crisis: support the airway first, sort the antibodies later

1️⃣6️⃣ Advanced MCQ Bank — Myasthenia Gravis & Crisis

15 questions. 15 lessons. Each with a reason.

1. A 28-year-old woman presents with fluctuating ptosis and diplopia. Reflexes are normal. What is the next best step?

A. Brain MRI
B. Tensilon test
C. Anti-AChR antibody testing
D. Lumbar puncture

✅ Answer: C
Explanation: Anti-AChR antibodies are the first-line test in suspected MG. MRI and LP are less specific.

2. A patient with MG is scheduled for laparoscopic cholecystectomy. Which of the following medications should be avoided?

A. Rocuronium
B. Fentanyl
C. Propofol
D. Sevoflurane

✅ Answer: A
Explanation: Non-depolarizing NMBAs (like rocuronium) have exaggerated effects in MG and should be used cautiously or avoided.

3. Which of the following is most suggestive of cholinergic crisis rather than myasthenic crisis?

A. Dilated pupils and respiratory failure
B. Miosis, salivation, diarrhea
C. Bulbar weakness and ptosis
D. History of recent infection

✅ Answer: B
Explanation: Cholinergic crisis presents with muscarinic signs — SLUDGE symptoms.

4. A patient has a VC of 18 mL/kg and SBC of 12. What is the appropriate action?

A. Increase pyridostigmine
B. Begin non-invasive ventilation
C. Intubate and admit to ICU
D. Start high-dose steroids

✅ Answer: C
Explanation: SBC < 15 and VC < 20 indicate respiratory compromise — intubation required.

5. In MuSK-positive MG, which of the following is more likely?

A. Ocular MG with mild weakness
B. Good response to pyridostigmine
C. Severe bulbar involvement, early crisis
D. No thymoma association

✅ Answer: C
Explanation: MuSK+ MG presents with severe bulbar/respiratory symptoms and responds poorly to pyridostigmine.

6. Which EMG finding supports LEMS rather than MG?

A. Decrement with low-frequency stimulation
B. Jitter on SFEMG
C. Incremental response after high-frequency stimulation
D. Normal repetitive stimulation

✅ Answer: C
Explanation: LEMS shows an incremental CMAP response after rapid stimulation — classic presynaptic pattern.

7. Which of the following is true regarding pyridostigmine?

A. Onset of action is 12 hours
B. It reverses the underlying autoimmune process
C. Overuse can cause depolarization block
D. It increases ACh release

✅ Answer: C
Explanation: Overdosing pyridostigmine can lead to cholinergic crisis due to NMJ overstimulation.

8. A patient with MG develops acute weakness after starting ciprofloxacin. What is the next step?

A. Increase AChEi
B. Intubate and start IVIG
C. Administer neostigmine
D. Give high-dose steroids only

✅ Answer: B
Explanation: Fluoroquinolones can precipitate crisis — airway protection and immunotherapy are priority.

9. Which sign is most specific for myasthenic crisis requiring intubation?

A. Ptosis
B. Diplopia
C. SBC < 15
D. Difficulty walking

✅ Answer: C
Explanation: Single breath count < 15 strongly correlates with respiratory compromise.

10. What is the best confirmatory test in seronegative MG?

A. Anti-dsDNA
B. Repetitive nerve stimulation
C. ANA
D. ESR

✅ Answer: B
Explanation: RNS or SFEMG confirms MG in seronegative patients.

11. Which treatment combination is appropriate during myasthenic crisis?

A. IVIG + neostigmine
B. Steroids alone
C. IVIG + ventilatory support
D. Pyridostigmine + high-dose suxamethonium

✅ Answer: C
Explanation: Immunotherapy + airway protection is cornerstone in crisis.

12. A myasthenic patient fails to wean off the ventilator. Which factor is most likely responsible?

A. Hypokalemia
B. Poor NIF and weak cough
C. Normal VC and strong voice
D. Recent steroid taper

✅ Answer: B
Explanation: Inadequate respiratory muscle strength is the most common cause of extubation failure.

13. What is the initial ventilator mode for MG with no lung disease?

A. SIMV
B. APRV
C. Assist-Control Volume (AC-VC)
D. CPAP

✅ Answer: C
Explanation: AC-VC ensures full support and reliable tidal volumes in neuromuscular weakness.

14. A 65-year-old MG patient presents with constipation, dry mouth, and proximal weakness. Reflexes are absent. What is most likely?

A. Myasthenic crisis
B. Lambert-Eaton syndrome
C. GBS
D. ALS

✅ Answer: B
Explanation: LEMS features autonomic dysfunction, proximal weakness, and areflexia.

15. Which of the following is true regarding steroids in MG?

A. They worsen symptoms permanently
B. They should be given before IVIG
C. They may worsen MG transiently at first
D. They replace the need for other immunosuppressants

✅ Answer: C
Explanation: High-dose steroids may cause transient worsening before improvement begins.

1️⃣7️⃣ Final Words

Myasthenia Gravis is a disease of fluctuation, fatigue, and fragility, yet in every case lies the potential for stability, strength, and survival — if recognized early and managed wisely.

This guide was crafted to provide practical ICU protocols, differential clarity, and structured ventilatory strategies for one of the most delicate neuromuscular emergencies we face. From diagnosing seronegative patients to preventing cholinergic missteps, every line was written to protect the breath before it fades.

Whether you're managing an MG patient on a rural ward or responding to a code in the ICU, this guide is your anchor — a roadmap of reasoning for when muscle meets machine.

Stay structured. Stay vigilant. Act early. 🧠

📌 Prepared for Dr. Amir Fadhel – Specialist in Anesthesiology and Critical Care
📅 Created: 05/06/2025
📅 Last Updated: 05/06/2025

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