Although myasthenia gravis may affect any voluntary muscle, muscles that control eye and eyelid movement, facial expressions, and swallowing are most frequently affected. The onset of the disorder may be sudden. Symptoms often are not immediately recognized as myasthenia gravis.
In most cases, the first noticeable symptom is weakness of the eye muscles. In others, difficulty in swallowing and slurred speech may be the first signs. The degree of muscle weakness involved in myasthenia gravis varies greatly among patients, ranging from a localized form, limited to eye muscles (ocular myasthenia), to a severe or generalized form in which many muscles-sometimes including those that control breathing-are affected. Symptoms, which vary in type and severity, may include a drooping of one or both eyelids (ptosis), blurred or double vision (diplopia) due to weakness of the muscles that control eye movements, an unstable or waddling gait, weakness in the arms, hands, fingers, legs, and neck, a change in facial expressions, difficulty in swallowing and shortness of breath, and impaired speech (dysarthria).
This answer is based upon information from the National Institute of Neurological Disorders and Stroke.