It is believed that tumor cells trigger autoantibodies against surface determinants, which cross-react with similar epitopes at the presynaptic regions of the neuromuscular junctions. In LEMS associated with SCLC, the primary focus is to treat the tumor because the symptoms of LEMS improve as the cancer regresses. The first drug of choice in LEMS is 3,4-diaminopyridine. The drug alleviates fatigue and weakness in LEMS patients, and it is well tolerated in dosages of 40 to 60 mg daily. Sometimes, pyridostigmine is added.
Prednisone helps substantially.
The congenital myasthenic syndromes are a heterogeneous group of syndromes that cause a failure of neuromuscular transmission that is not autoimmune but rather the result of genetic defects in various molecules, enzymes, or channels at the neuromuscular junction.