Because MG is a disorder of the neuromuscular junction, it cannot cause any sensory or autonomic symptoms. It also does not cause any bowel or bladder symptoms. It should be considered in the presentation of any isolated and otherwise unexplained weakness. The key feature of weakness due to MG is its variability. Patients will experience a waxing and waning of strength throughout the day, with a tendency to fatigue later in the day, or even towards the end of a particular task.
Progressive difficulty chewing during a meal, for instance, is a common complaint.
Symptoms of weakness tend to worsen with various stressors, such as exertion, heat, infection, and in the post partum period. Extubation after general anesthesia, therefore, may be prolonged. Other drugs which may worsen MG include aminoglycosides, quinine, antiarrhymthmics, and muscle relaxants. On examination the key feature is fatigable weakness, with normal sensation, reflexes, and coordination. Ptosis and diplopia can be elicited with sustained upward gaze for 30-60 seconds.