Lambert-Eaton myasthenic syndrome

Lambert-Eaton myasthenic syndrome (LEMS) is a rare neuromuscular junction disorder of paraneoplastic or primary autoimmune etiology.


LEMS is the second most common neuromuscular junction disease after myasthenia gravis.

Two-thirds of LEMS present as a paraneoplastic syndrome secondary to malignancy, most commonly lung cancer, less commonly breast, ovarian and pancreatic cancer and lymphoma.

Clinical presentation

The most common clinical feature is progressive proximal leg weakness. Deep tendon reflexes are almost always decreased. A less prominent but characteristic feature is autonomic dysfunction, most commonly dry mouth. Less common features include oropharyngeal and ocular symptoms related to weakness, such as dysphagia, dysarthria, ptosis, and diplopia.

The diagnosis is confirmed by electrodiagnostic studies and serology. Specifically, repetitive nerve stimulation demonstrates an increase in compound muscle action potential after increasing the stimulation frequency or after exercise, a phenomenon known as postactivation facilitation. Antibodies against the P/Q-type voltage-gated calcium channel are relatively specific for the diagnosis.

Radiographic features

A diagnosis of LEMS should prompt a search for an underlying malignancy, at least including chest CT, with additional consideration of FDG-PET . These studies most commonly reveal a tumor corresponding to small cell lung carcinoma.