[Neurogenic electromyographic activity in a patient with non-paraneoplasic Lambert-Eaton syndrome]

Lambert-Eaton myasthenic syndrome (LEMS) is a rare presynaptic disorder of the neuromuscular junction. Electrodiagnosis is characterized by compound muscle action potentials of small amplitude at rest, normalizing immediately after brief exercise or high-rate nerve stimulation. Needle electromyographic (EMG) activity is classically described as normal or myogenic.

We report the case of a young patient with a non-paraneoplastic LEMS in whom the initial electroneuromyographic examination showed neurogenic changes in needle EMG concomitant with typical features of presynaptic neuromuscular junction disorder at single and repetitive nerve stimulation.

Neurogenic EMG abnormalities were not previously described in patients with LEMS and could result from "functional" reversible denervation, depending on the presence of anti-calcium channel antibodies at axon terminals.

Neurogenic features in needle EMG examination in case of subacute motor deficiency should not eliminate the possibility of a presynaptic neuromuscular junction disorder, such as LEMS.