MG = post-synaptic disease that worsens with exertion 
– associated with thymomas 
– Symptomatic Tx: pyridostigmine 

LEMs = presynaptic disease that improves with exertion 
– associated with malignancy, most commonly small cell lung cancer (SCLC) 
– Symptomatic Tx: 3,4 DAP 

MG tested with 2-3 Hz repetitive stimulation, while LEMS can be tested with 50Hz repetitive stimulation (which is asked on exams but rarely used clinically because its very uncomfortable for patients)