Proximal Median Nerve Conduction Velocity Slowing in Carpal Tunnel Syndrome: An Observational Retrospective Study.

Background: Carpal Tunnel Syndrome (CTS) is the most common entrapment neuropathy, characterised by compression of the median nerve at the wrist. Traditional understanding views CTS as a distal compression issue, but recent evidence suggests potential proximal involvement.

Purpose: This study aimed to assess the prevalence of proximal median nerve conduction velocity (CV) slowing in CTS patients and examine its association with CTS severity.

Methods: In this retrospective observational study, data were analysed from 80 CTS patients and 40 controls from the Electrophysiology Lab at a tertiary care institute. Nerve conduction studies (NCS) evaluated the median nerve's conduction velocity and latency. Patients were classified by CTS severity, and nerve conduction parameters were statistically compared between groups.

Results: CTS patients exhibited significantly prolonged distal motor latency (DML) (5.2 ± 0.8 ms) and reduced forearm motor conduction velocity (MCV) (55.3 ± 4.1 m/s) compared to controls (P < .01). Approximately 27.45% of CTS hands showed proximal median nerve slowing. The severity classification showed that Grade 3 CTS was the most prevalent (47%), followed by Grade 2 (23%) and Grade 1 (10%). There was a negative correlation between distal latency and forearm conduction velocity, suggesting that as distal latency increases, forearm conduction velocity decreases. Post-operatively, significant improvements were observed in distal latency (mean decrease: 1.2 ± 0.5 ms, P < .01), but median nerve conduction velocity remained unchanged. While there was a trend towards improvement in CMAP amplitude, the difference did not reach statistical significance.

Conclusion: A subset of CTS cases exhibits reduced proximal median nerve conduction velocity, which correlates with CTS severity. This suggests retrograde degeneration may contribute to CTS pathology, challenging the traditional view of CTS as a purely distal compression disorder.