Child Neurology: Diagnosis of Lambert-Eaton myasthenic syndrome in children

Abstract

Objective: To report a case of Lambert-Eaton myasthenic syndrome (LEMS) in a child and review the existing literature of LEMS in children. Methods:We report a pediatric case of LEMS with the classic clinical triad of proximal weakness, autonomic dysfunction, and areflexia; the characteristic increment in compound motor action potential on high-frequency repetitive nerve stimulation; and positive serum P/Q-type voltagegated calcium channel antibodies. Only 11 pediatric cases of LEMS have been reported in the literature.Results: The patient's presentation with LEMS led to the diagnosis of occult neuroblastoma.Based on review of the existing pediatric literature, no consistent clinical or electrodiagnostic criteria exist to diagnose LEMS in children.Conclusions: There exists a need for consistent clinical criteria and electrodiagnostic testing for prompt diagnosis of LEMS in children. Prompt identification of LEMS will alert the physician to search for malignancy or another immune-mediated process. Paraneoplastic syndromes are immune-mediated phenomena that occur in a location remote to the primary neoplasm. The incidence of these syndromes is rare in adult cancers. The incidence is unknown in the pediatric population.Lambert-Eaton myasthenic syndrome (LEMS) is an immune-mediated disorder of neuromuscular transmission. The classic clinical presentation is proximal weakness, areflexia, and autonomic dysfunction. Antibodies to the P/Q-type voltage-gated calcium channel are present in 85%-90% of adult patients with LEMS.1 These antibodies interfere with quantal acetylcholine release from the presynaptic terminal of the neuromuscular junction and functional loss of voltage-gated calcium channels. Thus, less calcium enters the presynaptic terminal with the action potential, resulting in decreased release of acetylcholine. Nerve conduction studies characteristically show low compound motor action potential (CMAP) amplitudes.1 Facilitation, or an incremental increase in the amplitude of the CMAP, is seen upon high-frequency repetitive stimulation or following exercise testing. This is a finding highly specific for LEMS. 1 LEMS is a rare disorder in adults, most often seen as a paraneoplastic process with small-cell lung cancer. LEMS is even rarer in children, and only 11 pediatric cases have been reported in the literature (table). 2-10 Neoplasm was associated with 4 of these cases. 4,6 We present the case of a 3-year-old boy with LEMS, supported by the clinical presentation, characteristic findings on EMG, and elevated serum P/Q-type voltage-gated calcium channel antibodies.Case report. A previously healthy 3-year-old boy was admitted for evaluation of proximal weakness and ptosis, and for treatment of severe constipation that developed over a 4-to 5-month period. CSF was normal. MRI of the brain was unremarkable. The child's ptosis and extremity weakness improved without treatment over several days and he was discharged home. He returned approximately 1 week later with quadriparesis, worsened ptosis, and areflex...

Incidence and Ocular Features of Pediatric Myasthenias

“…Regarding other types of myasthenia, we found no patients in the population-based cohort with Lambert-Eaton syndrome and very few patients with confirmed antibody positive Lambert-Eaton myasthenia overall (2 cases over a 50-year period), similar to a recent report. 19 We did not report a single case of neonatal autoimmune myasthenia, similar to a study in the UK that found neonatal myasthenia to be extremely rare (3 children per year). 11 There are a number of limitations to the findings of this study.…”

Sympathetic innervation controls homeostasis of neuromuscular junctions in health and disease

“…Recently, sympathicomimetics (SM) have been introduced successfully as clinical treatment of neuromuscular transmission disorders called congenital myasthenic syndromes (CMSs) (3,4). Fittingly, muscle weakness is a hallmark of several autonomous nervous system disorders, including chronic fatigue syndrome (5), congenital insensitivity to pain (6), adrenal insufficiency (7,8), complex regional pain syndromes (9,10), and Lambert-Eaton myasthenic syndrome (11)(12)(13). Because, furthermore, beta-blockers lead to increased susceptibility to muscle fatigue (14) and modulate neuromuscular activity of drugs applied during anesthesia (15), we became interested in addressing sympathetic innervation of skeletal muscle.…”

Utility and practice of electrodiagnostic testing in the pediatric population: An AANEM consensus statement

“…There are case reports of infants with CMS (including choline acetyltransferase deficiency caused by CHAT mutations) who have subsequently been found to have abnormalities on fast or prolonged RNS . Although these diagnoses are individually rare, all have potential clinical implications if overlooked, including apnea (botulism or CHAT mutations) or paraneoplastic causes (LEMS) …”