Single-Center Study Evaluating the Impact of Age on the Diagnostic Performance of the Sural-to-Radial Sensory Amplitude Ratio in Length-Dependent and Non-Length-Dependent Peripheral Polyneuropathies

Peripheral sensory polyneuropathies are commonly classified as length-dependent (LDN) or non-length-dependent (NLDN) based on their clinical and electrophysiological features. This distinction is clinically important because it guides etiological investigations and therapeutic management. The sural-to-radial sensory nerve amplitude ratio (SRAR) is an electrophysiological marker that has been proposed to improve the diagnosis of sensory polyneuropathies and to help differentiate LDN from NLDN. Although the SRAR has traditionally been considered independent of demographic characteristics, recent evidence suggests that it decreases with aging, raising concerns about the use of a single diagnostic threshold across all age groups. The impact of age on the diagnostic performance of the SRAR, particularly in patients with non-length-dependent polyneuropathies, remains poorly characterized. This retrospective single-center study will analyze clinical and electrophysiological data from patients evaluated at the Peripheral Neuromuscular Rare Disease Reference Center of Nice University Hospital between January 2013 and July 2026. The study aims to determine whether age-adjusted SRAR thresholds improve the diagnostic discrimination between length-dependent and non-length-dependent peripheral polyneuropathies.

Inclusion criteria

• Adults aged 18 years or older.
• Diagnosis of peripheral sensory polyneuropathy.
• Classification as length-dependent (LDN) or non-length-dependent (NLDN) based on clinical and electrophysiological findings.
• Available nerve conduction study including sural and radial sensory nerve amplitudes allowing calculation of the SRAR.
• Evaluated at the Peripheral Neuromuscular Rare Disease Reference Center, Nice University Hospital, between January 2013 and July 2026.

Exclusion criteria

• Missing or incomplete clinical or electrophysiological data preventing SRAR calculation.
• Unclassifiable neuropathy phenotype.
• Technical factors affecting the reliability of nerve conduction studies.