A 48 yr old woman presents to the medicine OPD with complaints of generalized weakness which she claims gets worse towards the end of day. At times she also claims to see objects indistinctly in overlapping pairs of two. She has lost 3 kgs in the past 8 months ,she prefers having food that is easy to chew. She doesn't drink or smoke. No significant past or family history .
Examination :CVS,Abdominal, Respiratory systems normal. Muscle power normal but on prolonged testing decreases. Muscle tone and coordination normal. Pupillary reflexes, eye movements normal , however on prolonged gazing both eyelids droop.
What are the major differential diagnoses?