Prolonged Median Motor Distal Latency: What If not Carpal Tunnel Syndrome but Acute Inflammatory Demyelinating Polyradiculoneuropathy?

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ABSTRACT Introduction: The wrist is the only segment where both sensory and motor conduction of the same nerve can be studied through routine nerve conduction studies. This study aims to evaluate how two diseases with different pathophysiologies, carpal tunnel syndrome (CTS) and acute inflammatory demyelinating polyradiculoneuropathy (AIDP), differ in terms of median nerve conduction at the wrist. Materials and Methods: Patients hospitalized and diagnosed as having Guillain–Barré syndrome between 2013 and 2021 were screened from the hospital database. Electrodiagnostic subtype classification was performed according to the Rajabally criteria, retrospectively. Patients with AIDP along with age-matched patients with CTS were re-evaluated. Only the data of patients with prolonged median motor distal latency (≥4.0 ms) were included and analyzed. Results: The motor distal latencies recorded in patients with AIDP were significantly more prolonged and the compound muscle action potential amplitudes were significantly lower than those with CTS (P ≤ 0.001). Among the recordable sensory responses, hands with AIDP revealed significantly lower sensory nerve action potential amplitudes than hands with CTS (P ≤ 0.001) although their peak latencies were shorter (P ≤ 0.001) and conduction velocities were faster (P ≤ 0.001). The motor distal latency of the median nerve in patients with AIDP was not correlated with the sensory peak latency, unlike in patients with CTS. Conclusion: Median nerve sensory response, if present, tends to conduct faster in AIDP compared with CTS although the motor distal latency is profoundly prolonged.