Can myasthenia gravis cause unilateral or bilateral ptosis?

Myasthenia Gravis Can Cause Both Unilateral and Bilateral Ptosis

Myasthenia gravis can cause both unilateral and bilateral ptosis, though bilateral ptosis is more common in the classic presentation of the disease. 1

Ptosis Characteristics in Myasthenia Gravis

• Ptosis is often the first symptom to appear in myasthenia gravis and may initially present as unilateral before progressing to bilateral involvement 2
• Ptosis in myasthenia gravis typically worsens with fatigue (prolonged upgaze) and may have an associated Cogan lid-twitch sign 1
• The ptosis is characteristically variable and fluctuating, worsening throughout the day or with continued muscle use 1
• Ptosis of the contralateral eye may worsen upon manual elevation of the more involved eyelid due to Hering's law 1
• Temporary improvement of ptosis may occur with rest or with the application of an ice pack (ice test) 1

Unilateral vs. Bilateral Presentation

• While bilateral ptosis is more common in myasthenia gravis, unilateral ptosis can be the initial or sole manifestation 3
• Myasthenia gravis can present atypically with persistent unilateral ptosis without the classic fluctuating pattern 3
• Unilateral ptosis in myasthenia gravis may be misdiagnosed as a third nerve palsy or stroke, especially when accompanied by facial weakness 3
• In cases that begin with unilateral ptosis, progression to bilateral involvement often occurs as the disease advances 2

Associated Ocular Findings

• Ptosis in myasthenia gravis is frequently accompanied by variable strabismus and diplopia 1
• Ocular saccades (rapid eye movements) are often slow in myasthenia gravis patients 1
• Pupils are typically not affected in myasthenia gravis, which helps differentiate it from third nerve palsy 1
• Extraocular muscles are particularly susceptible to fatigue due to their twitch fiber composition and fewer acetylcholine receptors 4

Disease Course and Progression

• 50% of patients with myasthenia gravis initially present with ocular symptoms only (typically ptosis and variable strabismus) 1
• 50-80% of patients with initial ocular symptoms develop generalized myasthenia within a few years 1
• Ocular myasthenia gravis affects only the levator, orbicularis oculi, and extraocular muscles 1
• Generalized myasthenia gravis involves bulbar, limb, and respiratory muscles in addition to ocular manifestations 1

Diagnostic Considerations

• The ice test (application of an ice pack over closed eyes for 2 minutes) may demonstrate a reduction of ptosis by about 2mm and is highly specific for myasthenia gravis 1
• Acetylcholine receptor antibodies are found in nearly all patients with generalized myasthenia but only in 40-77% of patients with ocular myasthenia 1
• Single-fiber electromyography is considered the gold standard for diagnosis in many centers and is positive in over 90% of patients with ocular myasthenia 1
• When evaluating unilateral ptosis, it's important to rule out other etiologies such as third nerve palsy, which typically affects the pupil (unlike myasthenia gravis) 1, 3

Clinical Pitfalls to Avoid

• Failing to consider myasthenia gravis in cases of unilateral ptosis after ruling out central etiologies 3
• Missing the diagnosis when ptosis presents without the classic fluctuating pattern 3
• Overlooking the possibility of progression from ocular to generalized myasthenia gravis, which can lead to life-threatening respiratory failure if not properly monitored 1
• Focusing only on the ptosis without evaluating for other subtle signs of neuromuscular junction dysfunction 1