The earliest symptoms are usually double vision, drooping eyelids, inability to smile, slurred speech, and difficulty swallowing. Diagnosis depends on the distribution of weakness and the patient's medical history, which characteristically includes episodes of weakness during exertion followed by a relatively rapid recovery. Additionally, patients may undergo electro-physiologic testing. The cause is unknown. Eventually, walking is impossible, the hands become useless, and death occurs after respiratory muscles lose the strength to maintain breathing.
Mental facilities remain normal throughout the course of the disease.
Diagnosis is made by assessing the patient's history, constellation of symptoms, and the exclusion of other causes. No effective treatment presently exists for this condition. It is invariably fatal.