Myasthenia gravis is an autoimmune disorder of neuromuscular transmission that results in weakness of multiple muscle groups. The disease is antibody-mediated with a T-cell–modulated attack on postsynaptic acetylcholine receptors at the neuromuscular junction. The two clinical presentations of myasthenia gravis are ocular and generalized disease. In ocular disease, weakness is limited to the eyelids and extraocular muscles, whereas in generalized disease, bulbar (eg, dysarthria, dysphagia), limb, and respiratory muscles may be involved in addition to the eyes. More than half of myasthenia gravis patients present with ptosis and/or diplopia. Ptosis can alternate from eye to eye with severity waxing and waning. Extraocular muscle weakness may manifest as binocular diplopia, with early symptoms presenting simply as blurry vision. The pupils are always spared in myasthenia gravis, differentiating it from other extraocular movement disorders.
Management and Disposition
Patients with suspected myasthenia gravis warrant neurologic consultation. Initial therapy for patients includes oral acetylcholinesterase inhibitors (pyridostigmine). For severe disease (myasthenic crisis) that is rapidly progressive or results in respiratory compromise, therapies can include plasma exchange, IV immunoglobulin, and systemic glucocorticoids.
Ocular manifestations (ptosis, extraocular muscle deficits) may be the 1st sign of myasthenia gravis and should be recognized in the ED.
The “ice pack test” can be used in evaluation of patients with ptosis. Place a bag of ice over the closed lid for 2 minutes. Improvement of ptosis is a positive test result; neuromuscular transmission improves with decreased temperature.
Myasthenic crisis is life threatening, resulting in severe oropharyngeal and/or respiratory muscle weakness requiring intubation and ventilatory support.
Myasthenia Gravis with Ptosis. Patient with ptosis of left eye associated with myasthenia gravis before the ice pack test. (Photo contributor: Lawrence B. Stack, MD.)
Myasthenia Gravis with Ptosis. Patient with resolved ptosis of left eye after ice pack test. (Photo contributor: Lawrence B. Stack, MD.)