It is thought that the reason particular muscles are affected more frequently and severely than others is due to the differential temperature of various muscles in the body. Myasthenia gravis that effects the eye muscles in particular is typically referred to as ocular myasthenia gravis. This is a common form of the disorder, and it is characterized by droopy eyelids, and observable problems with eye coordination and object tracking. Generalized myasthenia gravis often includes ocular muscles, but in this case the symptoms have also been extended to muscles throughout the body. In particular, shoulder, limb, and muscles used for postural corrections are affected.
Myasthenic symptoms tend to fluctuate over the course of the hour and throughout the day.
They are often worst at night. Many physical and environmental conditions can either exacerbate or diminish the symptoms of myasthenia gravis. The muscle fatigue associated with myasthenia gravis is made worse by repetitive activity, excessive heat, overexertion, and emotional stress. Also known to make symptoms worse are abnormal thyroid activity and low potassium levels. Drugs that interfere with muscle activity, such as muscle relaxants, anesthetics, anticonvulsants, antiarrhythmics, some antibiotics, curariform agents and other drugs that interfere with neuromuscular transmission will also greatly increase the severity of the symptoms.