Myasthenia gravis is a disorder in which antibodies directed against acetylcholine receptors cause muscle dysfunction. Onset in childhood is uncommon. A transient neonatal form, caused by the placental transfer of acetylcholine receptor antibodies of mothers with myasthenia gravis, exists but usually subsides rapidly. Another variant is not immune mediated and exhibits a familial predisposition.
The disease may be purely ocular. In its most severe form, it frequently occurs as part of a major systemic disorder that involves other skeletal muscles, especially in patients who have not received immunosuppressive therapy. Generalization to systemic myasthenia is less common in childhood-onset ocular myasthenia than in the adult-onset form.
See BCSC Section 5, Neuro-Ophthalmology, for an in-depth discussion of the diagnosis of myasthenia gravis, along with its ocular and systemic aspects. Additional information is available on the website of the Myasthenia Gravis Foundation of America (www.myasthenia.org).
The principal ocular manifestation of myasthenia gravis is weakening of the EOMs, including the levator muscle. Most cases (90%) exhibit both ptosis and limited ocular rotations (Fig 12-8). The ocular signs can resemble those of any unilateral or bilateral ophthalmoplegia, including internuclear ophthalmoplegia.
Table 12-1 compares the features of TED with those of CPEO and myasthenia gravis.
Figure 12-8 Myasthenia gravis. Bilateral ptosis (right more than left) with right hypotropia.
Table 12-1 Differentiation of Conditions Producing Ptosis and Extraocular Muscle Involvement
A full discussion of treatment of the various forms of myasthenia gravis is beyond the scope of this chapter. In adults, the ocular manifestations are frequently resistant to the usual systemic myasthenia treatment. However, pediatric ocular myasthenia is often successfully managed with pyridostigmine alone. In adults and children in whom the ocular deviation has stabilized, standard eye muscle surgery can help restore binocular function in at least some gaze positions. Ptosis occasionally requires surgical repair.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.