Ultrasound-Confirmed Median Nerve Pseudoconduction Block due to Anatomical Variation

Area of Science:

• Neurology
• Neurophysiology
• Diagnostic Imaging

Background:

• Conduction block (CB) at non-entrapment sites is a key electrodiagnostic (EDX) finding for acquired demyelinating neuropathies.
• Anatomical variations can lead to pseudoconduction block, which mimics true CB and complicates EDX interpretation.

Purpose of the Study:

• To assess the frequency of anatomical variations causing median nerve pseudoconduction block.
• To evaluate the impact of these variations on EDX interpretation.
• To determine the role of neuromuscular ultrasound (NMUS) in improving diagnostic accuracy.

Main Methods:

• A retrospective review of upper limb NMUS scans performed by a single specialist.
• Measurement of the distance between the median nerve and brachial artery at the antecubital fossa.
• Review of available EDX data for cases with significant nerve-artery separation.

Main Results:

• Sixty-eight patients were included; the median nerve was consistently medial to the brachial artery.
• 10.3% of patients exhibited nerve-artery separation greater than 12.5 mm.
• Among those with significant separation and available EDX data, 60% showed evidence of complete or partial CB.

Conclusions:

• Neuromuscular ultrasound (NMUS) is valuable in differentiating pseudoconduction block from true CB.
• Accurate localization of the median nerve relative to the brachial artery using NMUS can prevent misdiagnosis.
• Specific stimulation points are suggested for improved accuracy when median nerve pseudoconduction block is suspected.