Electrophysiological diagnostic criteria of Lambert-Eaton myasthenic syndrome.
Various parameters of the repetitive nerve stimulation (RNS) test of the abductor digiti quinti muscle were analyzed statistically in 34 patients with Lambert-Eaton myasthenic syndrome (LEMS). The sensitivity and specificity of the increments after exercise and after 50-HZ stimulation for the diagnosis of LEMS were compared with reference values in 40 normal subjects and data from 538 tests in patients with myasthenia gravis (MG). When we used a 100% increment (the "gold standard") as the normal limit for the postexercise facilitation (PEF) or the high-rate stimulation (HRS) test, the diagnosis of LEMS was confirmed in 29 (85%) cases. When a 60% increment was used as the normal limit, the diagnosis of LEMS was made in 97% of cases. In MG, a 60% increment was observed in only 4 of 538 cases by HRS and in none by the exercise test. Thus, the use of a 60% increment showed a sensitivity of 97% for the diagnosis of LEMS and a specificity of 99% in excluding MG. A 60% increment in either the PEF or HRS test for the diagnosis of LEMS is a desirable alternative to the 100% increment previously considered to be the gold standard for this diagnosis.
Oh
Shin J
SJ
Department of Neurology, University of Alabama at Birmingham, Department of Veterans Affairs Medical Center, UAB Station, Birmingham, Alabama 35294, USA. shinjoh@uab.edu
Kurokawa
Katsumi
K
Claussen
Gwen C
GC
Ryan
Hewitt F
HF
D000200:Action Potentials / Q000502:physiology*; D003937:Diagnosis, Differential; D004558:Electric Stimulation; D004594:Electrophysiology / Q000379:methods; D015444:Exercise / Q000502:physiology; D006801:Humans; D015624:Lambert-Eaton Myasthenic Syndrome / Q000175:diagnosis* / Q000503:physiopathology; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000503:physiopathology*; D009157:Myasthenia Gravis / Q000175:diagnosis / Q000503:physiopathology; D012146:Rest / Q000502:physiology; D012189:Retrospective Studies; D012680:Sensitivity and Specificity