How to Suspect Myasthenia Gravis
Suspect myasthenia gravis in any patient presenting with fatigable or fluctuating muscle weakness that worsens with repeated use and improves with rest, particularly when ocular symptoms (ptosis, diplopia) or bulbar symptoms (dysphagia, dysarthria) are present. 1
Key Clinical Features to Recognize
Cardinal Symptom Pattern
- Fatigable weakness is the hallmark: muscle weakness that worsens with activity and improves with rest 1, 2
- Fluctuating symptoms throughout the day, typically worse in the evening 3
- Weakness is generally more proximal than distal 1
Ocular Manifestations (Most Common Initial Presentation)
- Ptosis (drooping eyelids beyond 1-2 mm of the upper limbus) occurs in approximately 90% of MG patients 4, 5
- Diplopia (double vision) from extraocular muscle weakness 1, 4
- Ophthalmoplegia (abnormal eye movements) 1
- Up to 50% of patients will have exclusively ocular symptoms initially, and in approximately 20% the disease remains confined to ocular muscles 4, 5
Bulbar and Facial Involvement
- Dysphagia (difficulty swallowing) 1
- Dysarthria (difficulty speaking) 1
- Facial muscle weakness 1
- Drooling 6
Generalized Symptoms
- Difficulty climbing stairs (proximal leg weakness) 6
- Hoarseness 6
- Dyspnea or shortness of breath with light activity 1
Simple Bedside Diagnostic Tests
Ice Pack Test (Highly Specific)
- Apply an ice pack over closed eyes for 2 minutes and observe for reduction in ptosis 1, 7, 8
- This test is highly specific for myasthenia gravis, particularly for ocular symptoms 1, 7
- Can be performed immediately in the office without special equipment 7
Clinical Observation
- Ask the patient to sustain upgaze for 30-60 seconds and watch for progressive ptosis 4
- Observe for worsening diplopia with prolonged lateral gaze 4
- Test for fatigability by having the patient perform repetitive movements 2
Critical Red Flags and Exacerbating Factors
Triggering Conditions
- Intercurrent infection (bacterial or viral respiratory infections are most common) 3
- Fever 3
- Physical or emotional exhaustion 3
High-Risk Situations Requiring Immediate Evaluation
- Respiratory muscle weakness with dyspnea—50-80% of patients with initial ocular symptoms may develop generalized myasthenia within a few years 1, 8
- Bulbar symptoms with risk of aspiration 1
- Any patient with suspected MG requiring surgery must have serum anti-acetylcholine receptor antibody levels measured preoperatively to avoid respiratory failure during anesthesia 6
Common Pitfalls to Avoid
Medication-Induced Exacerbation
Immediately review the patient's medication list and avoid or discontinue medications that worsen myasthenia 1, 7, 8:
- β-blockers 1, 7, 8
- IV magnesium 1, 7, 8
- Fluoroquinolones 1, 7, 8
- Aminoglycosides 1, 7, 8
- Macrolide antibiotics 1, 7, 8
Diagnostic Considerations
- Do not dismiss the diagnosis if symptoms are purely ocular—this occurs in 50% of initial presentations 4, 5
- Remember that visual disturbances may be the only presenting complaint 2
- Symptoms may be intermittent and variable, making diagnosis challenging 4, 3
When to Refer Urgently
Immediate Neurology Referral Indicated For:
- Any patient with positive ice pack test or strong clinical suspicion 1, 8
- Respiratory symptoms or difficulty breathing 1
- Rapidly progressive weakness 8
- Bulbar symptoms with aspiration risk 1
Pre-Surgical Screening
- All patients suspected of having thymomas (even without symptoms) should have serum anti-acetylcholine receptor antibody levels measured before any surgical procedure 6
- Approximately 30-50% of patients with thymomas have myasthenia gravis 6