Related Experiment Video
Updated: May 9, 2026

Screening of Axonal Degeneration in Carpal Tunnel Syndrome Using Ultrasonography and Nerve Conduction Studies
Published on: January 11, 2019
Ulnar sensory-motor amplitude ratio: a new tool to differentiate ganglionopathy from polyneuropathy
Raphael Ubirajara Garcia1, João Adilson Gama Ricardo, Cassiana Abreu Horta
1Department of Neurology, School of Medicine, University of Campinas (UNICAMP), Campinas SP, Brazil.
Unlabelled:
The objective of this study was to evaluate if the ratio of ulnar sensory nerve action potential (SNAP) over compound muscle action potential (CMAP) amplitudes (USMAR) would help in the distinction between ganglionopathy (GNP) and polyneuropathy (PNP).
Methods:
We reviewed the nerve conductions studies and electromyography (EMG) of 18 GNP patients, 33 diabetic PNP patients and 56 controls. GNP was defined by simultaneous nerve conduction studies (NCS) and magnetic resonance imaging (MRI) abnormalities. PNP was defined by usual clinical and NCS criteria. We used ANOVA with post-hoc Tukey test and ROC curve analysis to compare ulnar SNAP and CMAP, as well as USMAR in the groups.
Results:
Ulnar CMAP amplitudes were similar between GNP x PNP x Controls (p=0.253), but ulnar SNAP amplitudes (1.6±3.2 x 11.9±9.1 × 45.7±24.7) and USMAR values (0.3±0.3 × 1.5±0.9 × 4.6±2.2) were significantly different. A USMAR threshold of 0.71 was able to differentiate GNP and PNP (94.4% sensitivity and 90.9% specificity).
Conclusions:
USMAR is a practical and reliable tool for the differentiation between GNP and PNP.
Related Concept Videos
Local Anesthetics: Differential Sensitivity of Nerve Fibers
Peripheral Arterial Disease II: Clinical Manifestations and Diagnostic Evaluation
