leventhal , et al . identified four risk factors felt to have predictive value , namely : ( 1 ) duration of myasthenia gravis greater than or equal to 6 years , ( 2 ) chronic respiratory disease , ( 3 ) dose of pyridostigmine greater than or equal to 750 mg per day , and ( 4 ) vital capacity less than or equal to 2.9 litres .
C0026896
myasthenia gravis
C0034261
pyridostigmine