The manifestation of periodic paralysis muscle weakness is mostly weakness of the limbs, which appears in the morning when you wake up or during the night when you go to bed, while myasthenia gravis often appears first with paralysis of the eye muscles and the weakness has a fatigue-prone character, manifesting itself as light in the morning and heavy at night.
In addition, periodic paralysis is associated with alterations in serum potassium and electrocardiographic abnormalities, while myasthenia gravis fatigue tests and neostigmine tests are both positive, all of which help to differentiate it.