Symptoms of Myasthenia Gravis
Myasthenia gravis presents with fluctuating, fatigable muscle weakness that worsens with activity and improves with rest, most commonly beginning with ocular symptoms (ptosis and diplopia) before potentially progressing to bulbar, limb, and respiratory muscle involvement. 1
Ocular Manifestations (Most Common Initial Presentation)
- Ptosis (drooping eyelids) is often the first symptom, appearing unilateral or bilateral, characteristically worsening with sustained upward gaze or prolonged activity and improving after rest 1, 2
- Diplopia (double vision) results from extraocular muscle weakness, is highly variable throughout the day, and changes with different directions of gaze 1, 2
- Variable strabismus (misalignment of the eyes) that fluctuates during examination is characteristic 1
- Pupils are NOT affected—this is a critical distinguishing feature; pupillary abnormalities should prompt immediate consideration of alternative diagnoses such as third nerve palsy 1, 2
Approximately 50% of patients initially present with purely ocular symptoms, but 50-80% will progress to generalized disease within a few years, most commonly within the first two years 1, 3
Bulbar Manifestations
- Dysarthria (slurred speech) that worsens with prolonged talking as facial and pharyngeal muscles fatigue 1, 2
- Dysphagia (difficulty swallowing) that worsens with prolonged chewing—this is a particularly concerning red-flag symptom as it precedes myasthenic crisis in more than 50% of cases 1, 3, 2
- Facial muscle weakness causing reduced facial expressions or difficulty with facial movements 1
- Difficulty chewing that increases during meals 1
Limb and Axial Muscle Involvement
- Proximal muscle weakness affecting shoulders and hips more than distal muscles 1, 2
- Difficulty climbing stairs indicating lower limb weakness 3, 2
- Neck weakness leading to difficulty holding up the head 1, 2
- The weakness is characteristically more proximal than distal 3
Respiratory Manifestations (Life-Threatening)
- Respiratory muscle weakness represents the most serious and potentially fatal manifestation 1, 2
- Shortness of breath, particularly with exertion or light activity 1
- Diminished cough strength and ineffective clearance of secretions 3
- Inability to count to 15 on a single breath is a reliable clinical marker of imminent respiratory insufficiency 3
- Can rapidly progress to respiratory failure requiring intubation (myasthenic crisis) 1
Hallmark Clinical Characteristics
- Fluctuating weakness—symptoms vary throughout the day and can present with completely different patterns during repeated examination 1, 2
- Fatigability—symptoms worsen as the day progresses, with continued activity, or with repetitive use of affected muscles 1, 2
- Improvement with rest—temporary symptom relief occurs after several minutes of rest 1, 2
- Diurnal variation—weakness typically worsens later in the day 4
- Positive ice pack test—applying an ice pack over closed eyes for 2 minutes (ptosis) or 5 minutes (strabismus) produces improvement of ≥2 mm in ptosis or reduction in ocular deviation, providing a highly specific bedside indicator 1, 3, 2
Critical Pitfalls to Recognize
- Painless weakness—the presence of prominent pain should raise suspicion for alternative diagnoses such as myositis 1
- No sensory disturbances—numbness or tingling points away from myasthenia gravis toward conditions like Guillain-Barré syndrome 1
- Preserved consciousness—patients remain fully alert unless sedated; altered mental status suggests another etiology 1
- Variable presentation—myasthenia gravis is considered a "great masquerader" as it can mimic many types of eye movement disorders 1