Lowering the cutoff value for increment increases the sensitivity for the diagnosis of Lambert‐Eaton myasthenic syndrome

Abstract

Background Increment of compound muscle action potential amplitude is a diagnostic hallmark of Lambert‐Eaton myasthenic syndrome (LEMS). Making a diagnosis can be challenging, therefore, a proper cutoff for abnormal increment is highly relevant for improved recognition of this rare disease. Methods We determined the sensitivity and specificity of 60% and 100% cutoff values in all consecutive patients who underwent increment testing in our hospital from 1999 to 2016. Results We included 156 patients, 63 with LEMS and 93 without LEMS. Sensitivity of a 60% cutoff for increment testing was 77.8% (95% confidence interval 65.5%–87.3%) and 58.7% (45.6%–71.0%) for 100%. Specificity was 98.9% (94.2%–100%) and 100% (96.1%–100%) using a threshold of 60% and 100%, respectively. Conclusions Lowering the cutoff value for abnormal increment to 60% greatly increases sensitivity to diagnose LEMS without an overt loss in specificity.

Amifampridines are the Most Effective Drugs for Treating Lambert-Eaton Myasthenic Syndrome With a Focus on Pediatric Lambert-Eaton Myasthenic Syndrome

“…7 Our study showed that a CMAP increase of ≥60% provided a sensitivity of 96% and a specificity of 98% in diagnosing LEMS. 13 Lipka et al’s 19 study confirmed this finding.…”

Lambert‒Eaton Myasthenia Syndrome Initial Presentation Mimicking Myasthenia Gravis

“…Patients with LEMS experience peak muscle weakness in the morning that progressively improves through the day with exercise, whereas the opposite is true for patients with MG (9). This is reflected by EMG findings that show potentiation of compound muscle action potential (CMAP) with exercise or high frequency (10–50 Hz) repetitive nerve stimulation (RNS) in LEMS, whereas the opposite finding is seen with MG. A increase in CMAP amplitude of 60%–100% after RNS or isometric exercise is strongly suggestive of presynaptic neuromuscular junction disorder (10).…”

Neuromuscular junction disorders beyond myasthenia gravis

“…For assessment of facilitation, ≥ 100% increment in the CMAP at HRS or after 10 s exercise test is pathognomonic of LEMS [2]. Recent studies showed that ≥ 60% increment is sufficient for the diagnosis of LEMS with 97% diagnostic sensitivity and 98% diagnostic specificity [10,11].…”

“…Recent studies showed that ! 60% increment is sufficient for the diagnosis of LEMS with 97% diagnostic sensitivity and 98% diagnostic specificity [10,11].…”