Lambert-Eaton myasthenic syndrome (LEMS) is a neuromuscular disorder 
characterized by defective neurotransmitter release at presynaptic terminals. It 
is caused by an IgG autoantibody reacting against voltage-gated calcium 
channels. Severe LEMS complicated by ventilatory failure is rare. We report a 
case of small-cell lung cancer (SCLC) presenting with LEMS and ventilatory 
failure in a 67-year-old man who initially presented with progressive limb 
weakness for 6 months and tachypnea with shallow breathing for 1 week. LEMS was 
diagnosed through electrophysiologic studies. Chest radiography and computerized 
tomography showed a huge mass lesion over the left anterior and middle 
mediastinum with an encasement of the left pulmonary artery. Cytologic 
examination of ultrasound-guided fine needle aspiration disclosed SCLC. 
Successful treatment in combination with plasma exchange and chemotherapy 
resulted in dramatic tumor regression and LEMS remission, which were confirmed 
by chest radiography and electrophysiologic studies. This case suggests that 
plasma exchange and chemotherapy can be effective in treating SCLC with severe 
LEMS that produces ventilatory failure.