LambertEaton

LambertEaton, commonly known as Lambert-Eaton myasthenic syndrome (LEMS), is a rare autoimmune disorder of the presynaptic neuromuscular junction defined by proximal muscle weakness and autonomic symptoms. It results from autoantibodies that target voltage-gated calcium channels on nerve terminals, reducing calcium influx and acetylcholine release into the neuromuscular junction.

Most cases are paraneoplastic, with small cell lung carcinoma being the most frequently associated malignancy. About half of patients have an underlying cancer at presentation or discovered during follow-up; a smaller proportion is idiopathic. The clinical picture typically includes proximal, symmetrical weakness (often more pronounced in the legs), easy fatigability, and autonomic features such as dry mouth, constipation, orthostatic hypotension, or erectile dysfunction. Deep tendon reflexes may be reduced but are often improved with repeated use, a feature that helps distinguish LEMS from similar disorders.

Diagnosis relies on clinical assessment supported by electrophysiological and serological findings. Nerve conduction studies usually show reduced baseline CMAP amplitudes with a characteristic incremental response (often more than 100%) after high-frequency stimulation or brief exercise. Serology commonly detects antibodies against P/Q-type voltage-gated calcium channels. Imaging and workup for an underlying malignancy (often CT or PET-CT) are routine, alongside evaluation for other autoimmune mechanisms.

Treatment focuses on addressing the underlying cancer when present and improving neuromuscular transmission. Symptomatic therapy includes acetylcholinesterase inhibitors (for mild symptoms) and agents that increase acetylcholine release, such as 3,4-diaminopyridine derivatives. Immunomodulatory therapies (steroids, IVIG, plasmapheresis) are considered for more severe disease. Prognosis improves with cancer treatment and immunotherapy, though some patients retain residual weakness.