Acquired Presynaptic Neuromuscular Junction Disorders: Infant Botulism and Lambert-Eaton Myasthenic Syndrome

Two rare treatable acquired disorders of presynaptic neuromuscular junction are described. In infantile botulism, Clostridium botulinum toxin produced from intestinal colonization blocks docking proteins from releasing acetylcholine. Patients display bulbar signs and constipation, abnormal high-frequency repetitive nerve stimulation and positive stool toxin. However, treatment within 3 days of hospitalization with botulinum immunoglobulin results in reduced length of hospital stay by 3 weeks and ventilation by 2 weeks.Pediatric Lambert-Eaton Myasthenic Syndrome (LEMS) is a primary autoimmune disorder but less frequently paraneoplastic in less than half of patients. LEMS typically presents with leg weakness and areflexia. Supportive of LEMS diagnosis is a low amplitude compound muscle action potential facilitating >25% with 10-50. Hz stimulation or exercise. Patients respond well to 3,4-diaminopyridine as well as IVIg and immunosuppressive therapies.Although these are rare disorders, a high index of suspicion will lead to timely therapies and significant improvement in outcomes, and therefore they are well worth understanding.