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Tibial to ulnar nerve amplitude ratio as a marker of length-dependent neuropathy
Chikashi Yano1, Tomonori Nakamura1, Masahiro Ando1
1Department of Neurology and Geriatrics, Kagoshima University Graduate School of Medical and Dental Sciences, Kagoshima, Japan.
Objective:
To evaluate the utility of nerve conduction studies as a marker of length-dependent neuropathy.
Methods:
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.
Results:
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.
Conclusions:
The T/U CMAP amplitude ratio is a simple, robust electrophysiological index of length-dependent neuropathy.
Significance:
This marker offers a reliable and accessible way to distinguish between acquired and inherited neuropathies, improving diagnostic accuracy and helping prioritize genetic testing.
