Eaton-Lambert syndrome, also known as Lambert-Eaton myasthenic syndrome or LEMS, is a rare autoimmune disorder. It occurs when antibodies attack the nerve cells, damaging the cells responsible for regulating the amount of neurotransmitter released. These neurotransmitters are what cause muscles to contract. 

It is characterized by fatigue and weakness of the muscles, particularly the thigh and pelvic muscles. Early symptoms of Eaton-Lambert syndrome include problems going upstairs, standing from a sitting position and lifting arms over the head. It may also impact involuntary body functions and result in dry mouth and impotence. 

Eaton-Lambert syndrome is often associated with underlying cancer, so treatment of the syndrome often starts with treatment of the cancer, which may involve chemotherapy, radiation therapy or surgery. Medication to improve neuromuscular transmission, such as guanidine or pyridostigmine, and plasma exchange may also be considered.