Myasthenia Gravis (MG)

Signs and Symptoms

Myasthenia gravis (MG) weakens and fatigues the body’s voluntary muscles (those we can move at will). It does not damage the musculature of the heart or the gastrointestinal tract.

MG can affect any of the body’s voluntary muscles, but it tends to affect the muscles that control movement of the eyes and eyelids, causing ocular weakness. Consequently, a partial paralysis of eye movements (ophthalmoparesis), double vision (diplopia), and droopy eyelids (ptosis) are usually among the first symptoms of MG. More than 50% of patients present with ocular symptoms of ptosis and/or diplopia. Of those who present with ocular manifestations, about half will develop generalized disease within two years. ^1,2,3

In generalized MG, weakness tends to spread sequentially from the face and neck to the upper limbs, the hands, and then the lower limbs. It may become difficult to lift the arms over the head, rise from a sitting position, walk long distances, climb stairs, or grip heavy objects.

Weakness and fatigue in the neck and jaw also can occur early in MG. This bulbar weakness — named for the nerves that originate from the bulblike part of the brainstem — can cause difficulty with talking (dysarthria), chewing, swallowing (dysphagia), and holding up the head. About 15% of patients present with bulbar symptoms. Bulbar weakness tends to give speech a slurred, nasal quality. It also can lead to frequent choking spells and make eating unpleasant and tiresome.

Limb weakness alone is highly uncommon and can be seen in only 5% of MG patients. In some rare cases, weakness may spread to muscles in the chest that control breathing.

Disease course

Weakness and fatigue in MG tend to fluctuate from day to day, and even during a single day. People with the disease are often strongest in the morning after a full night’s sleep and weakest in the evening. Exercise may also affect the weakness and fatigue experienced by those living with MG.

Over a longer term, the symptoms of MG usually progress, reaching maximum or near-maximum severity within one to three years of onset in most people. In about 15% of people, the disease remains ocular, but in most it becomes oculobulbar or generalized.

Weakness serious enough to require full-time wheelchair use is not common in MG. Most people, when properly treated, find they can remain physically active.

Remission, a reversal of some or all symptoms, occurs in about 20% of people with MG. Usually, the remissions are temporary, with an average duration of five years, but some people experience more than one remission during their lifetime. A few people have experienced apparently permanent remissions, lasting more than 20 years.

Compared to adult-onset MG, juvenile MG tends to progress more slowly and has a higher incidence of remission. Historically, many children given diagnoses of juvenile MG turned out to have a congenital myasthenic syndrome.

References

1. GROB, D., ARSURA, E. L., BRUNNER, N. G. & NAMBA, T. The Course of Myasthenia Gravis and Therapies Affecting Outcome. Ann. N. Y. Acad. Sci. (1987). doi:10.1111/j.1749-6632.1987.tb51317.x
2. Bever, C. T., Aquino, A. V., Penn, A. S., Lovelace, R. E. & Rowland, L. P. Prognosis of ocular myasthenia. Ann. Neurol. (1983). doi:10.1002/ana.410140504
3. Sommer, N., Melms, A., Weller, M. & Dichgans, J. Ocular myasthenia gravis - A critical review of clinical and pathophysiological aspects. Doc. Ophthalmol. (1993). doi:10.1007/BF01215447