A patient who develops bilateral ptosis and generalized weakness undergoes repetitive nerve stimulation. The result is recorded above.

a. What does the recording show?

b. What is the diagnosis?

 

Answer to a
The electromyogram (EMG) shows progressive increase in the muscle
action potentials with repetitive nerve stimulation (this is delivered at 
a rate of 2 to 3 Hz to the motor nerve).

 
Answer to bLambert-Eaton's syndrome. 
In myasthenia gravis, the reverse is true ie, the muscle action potentials 
decreases with repetitive nerve stimulation. (Note: ptosis is commoner in myasthenia than in Lambert-Eaton's syndrome).