Tibial to ulnar nerve amplitude ratio as a marker of length-dependent neuropathy

TL;DR

A new nerve conduction measure helps distinguish between acquired and inherited neuropathies with high accuracy.

Contribution

The tibial to ulnar nerve amplitude ratio is introduced as a novel diagnostic marker for length-dependent neuropathy.

Findings

The tibial to ulnar amplitude ratio is significantly higher in CIDP compared to CMT patients.

The ratio has 95.5% sensitivity and 85.5% specificity for distinguishing CIDP from CMT.

The marker performs well in CIDP-mimicking CMT cases with similar accuracy.

Abstract

•Tibial to ulnar amplitude ratio separates acquired and inherited neuropathies.•The ratio is higher in chronic inflammatory demyelinating polyradiculoneuropathy.•Area under the curve 0.95 with 95.5% sensitivity and 85.5% specificity.

Tibial to ulnar amplitude ratio separates acquired and inherited neuropathies.

The ratio is higher in chronic inflammatory demyelinating polyradiculoneuropathy.

Area under the curve 0.95 with 95.5% sensitivity and 85.5% specificity.

To evaluate the utility of nerve conduction studies as a marker of length-dependent neuropathy.

We conducted a retrospective study of 44 chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) patients and 365 genetically confirmed Charcot-Marie-Tooth disease (CMT) patients, including those with PMP22 duplications or mutations in GJB1, MFN2, MPZ, and MME. Nerve conduction study parameters were compared, with subgroup analyses of CIDP-mimicking CMT (genetically confirmed CMT with a prior clinical diagnosis of CIDP) and gene-based classifications. Receiver operating characteristic (ROC) analysis assessed the sensitivity and specificity of these parameters.

The tibial to ulnar nerve distal compound muscle action potential (T/U CMAP) amplitude ratio was significantly higher in CIDP patients compared to those with genetically confirmed CMT, CIDP-mimicking CMT, and gene-based subgroups. This ratio yielded the highest area under the curve (AUC: 0.95) among all evaluated parameters, with a cutoff value of 0.385 demonstrating high diagnostic sensitivity (95.5%) and specificity (85.5%). In CIDP-mimicking CMT group, a similar sensitivity and specificity were observed.

The T/U CMAP amplitude ratio is a simple, robust electrophysiological index of length-dependent neuropathy.

This marker offers a reliable and accessible way to distinguish between acquired and inherited neuropathies, improving diagnostic accuracy and helping prioritize genetic testing.

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