Signs and Symptoms of Myasthenia Gravis
Myasthenia gravis presents with fluctuating muscle weakness that characteristically worsens with activity and improves with rest, most commonly beginning with ocular symptoms (ptosis and diplopia) before potentially progressing to generalized weakness affecting bulbar, limb, and respiratory muscles. 1
Ocular Manifestations (Most Common Initial Presentation)
- Ptosis (drooping eyelids) is often the first symptom, appearing unilateral or bilateral, and characteristically worsens with prolonged upgaze or sustained activity 1
- Diplopia (double vision) results from extraocular muscle weakness and is highly variable in presentation 1
- Variable strabismus (misalignment of eyes) is characteristic, with the pattern changing during examination 1
- Slow ocular saccades (impaired rapid eye movements) are a characteristic finding 1
- Pupils are NOT affected—this is a critical distinguishing feature; pupillary involvement should immediately alert you to consider alternative diagnoses such as third nerve palsy 1, 2
Approximately 50% of patients initially present with ocular symptoms only, and 50-80% of these will develop generalized myasthenia within a few years 1
Bulbar Manifestations
- Dysarthria (slurred speech) occurs as facial and pharyngeal muscles fatigue 1, 3
- Dysphagia (difficulty swallowing) worsens with prolonged chewing 1, 3
- Facial muscle weakness causes reduced facial expressions 1, 3
- Difficulty chewing becomes progressively worse during meals 1
Limb and Axial Muscle Involvement
- Proximal muscle weakness affecting shoulders and hips more than distal muscles is characteristic 1, 2
- Neck weakness leading to difficulty holding up the head 1, 3
- Difficulty climbing stairs due to proximal lower extremity weakness 2
Respiratory Manifestations (Most Life-Threatening)
- Respiratory muscle weakness represents the most serious manifestation and can rapidly progress to respiratory failure (myasthenic crisis) 1, 2
- Shortness of breath, particularly with exertion 1
- Respiratory fatigue requiring close monitoring with pulmonary function tests (negative inspiratory force and vital capacity) 1, 3
Hallmark Clinical Characteristics
- Fluctuating weakness with symptoms worsening with continued activity and improving with rest 1, 4, 5, 6
- Fatiguability with symptoms worsening as the day progresses or with repetitive use of affected muscles 1, 3, 7
- Variable presentation with the pattern of weakness changing during examination 1
- Temporary improvement with rest or ice application (ice pack test is highly specific for ocular symptoms) 1, 2
- Bilateral but potentially asymmetric presentation 3
Critical Clinical Pitfall
Myasthenia gravis is considered a "great masquerader" as it can mimic many types of eye movement disorders 1. The key distinguishing feature is that muscle weakness worsens with repeated use and improves with rest 4, 5, 6, unlike mechanical restrictions (thyroid eye disease) or fixed neurologic deficits (third nerve palsy). Failure to recognize early respiratory involvement can be fatal, as all grades of myasthenia warrant thorough evaluation given the potential for rapid progression to respiratory compromise 1, 2.