C
In the Lambert-Eaton syndrome that typically develops in some patients who have small cell carcinoma of the lung, the autoantibodies to presynaptic voltage–dependent calcium channels of motor neurons reduce the release of acetylcholine in response to nerve stimulation. This abnormality causes muscle weakness that improves somewhat with repeated attempts to move the muscles, in contrast to myasthenia gravis, which is characterized by gradually progressive weakness, more pronounced after several contractions.