Clinical Presentation and Diagnostic Features of Myasthenia Gravis

Core Clinical Presentation

Myasthenia gravis is characterized by painless, fluctuating, fatigable muscle weakness that worsens with repetitive use and improves with rest, most often beginning with ocular symptoms such as ptosis and diplopia. 1
Approximately 50 % of patients initially present with purely ocular manifestations; of these, 50–80 % progress to generalized disease within a few years. 2, 1, 6

Ptosis typically worsens with prolonged upward gaze and fatigue and is often asymmetric. 2, 1
Binocular diplopia arises from variable, incomitant strabismus that changes pattern throughout the day. 2, 1
The Cogan lid‑twitch sign—brief eyelid overshoot when refixating from downgaze to primary position—is a specific ocular finding. 2, 3
Slow ocular saccades are frequently observed. 2, 4
Elevating the more affected eyelid manually can worsen contralateral ptosis (Hering’s law phenomenon). 2, 3
Pupillary function is generally preserved; rare cases show impaired or sluggish responses. 2, 5
The ice‑pack test improves ptosis after 2 minutes of cooling and strabismus after 5 minutes; typical improvement is ~2 mm reduction in ptosis and measurable correction of misalignment, and the test is highly specific for myasthenia gravis. 2, 3, 4

Dysarthria worsens with prolonged speech. 5
Dysphagia and difficulty chewing, especially with extended mastication, are common bulbar complaints. 5, 3
Patients may have difficulty maintaining head position. 5, 3
Motor weakness is variable but tends to affect proximal muscles more than distal ones. 5, 4
Respiratory muscle weakness can cause respiratory fatigue and, in severe cases, life‑threatening myasthenic crisis requiring ventilatory support. 5, 4, 2, 1

Symptoms intensify with repetitive muscle use and as the day progresses. 2, 3
Strabismus and diplopia may assume entirely different patterns after fatigue or repeated examinations. 2, 6
Rest leads to rapid improvement of weakness. 2, 3

Onset most commonly occurs in the third to fourth decade of life, though later onset is more frequent in males. 2, 1, 6
No geographic or racial predilection has been identified. 2, 1
The disease course is variable, with fluctuating symptoms over time. 2, 1

Thymoma is present in 10–20 % of patients with acetylcholine‑receptor antibody‑positive myasthenia gravis. 7
Approximately one‑third of individuals diagnosed with thymoma have concurrent myasthenia gravis. 7
Autoimmune thyroid disease increases the risk of developing myasthenia gravis. 2, 1
When thyroid eye disease coexists, lid retraction may be observed. 2, 3

Myasthenia gravis is often termed “the great masquerader” because its presentation can mimic many forms of incomitant strabismus with or without ptosis. 2, 1
The hallmark distinguishing feature is the variable nature of symptoms that change during examination and with fatigue, prompting consideration of myasthenia gravis over structural neurologic lesions. 2, 3