Myasthenia gravis (MG) weakens and fatigues the body’s voluntary muscles (those we can move at will). It doesn’t damage the musculature of the heart or the gastrointestinal tract.
Early in its course, MG 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.
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 make it difficult to talk, chew, swallow and hold up the head.
Bulbar weakness tends to give speech a slurred, nasal quality. It also can lead to frequent choking spells, and make eating unpleasant and tiresome.
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.
In some cases, weakness may spread to muscles in the chest that control breathing.
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.
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 percent of people, the disease remains ocular, but in most it becomes oculobulbar or generalized. If the disease remains ocular for three years, it usually doesn’t become 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 percent 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.