Anterior interosseous/median nerve latency ratio

Area of Science:

• Neurology
• Diagnostic Techniques
• Nerve Injury Evaluation

Background:

• Anterior interosseous nerve injuries, also known as Kiloh Nevin syndrome, present diagnostic challenges due to their predominantly motor nature.
• These injuries are frequently misdiagnosed as finger ligamentous injuries, complicating clinical assessment.

Purpose of the Study:

• To introduce and validate a novel electrodiagnostic technique for diagnosing anterior interosseous nerve injuries.
• To establish the utility of this technique in differentiating Kiloh Nevin syndrome from other neuropathies, including carpal tunnel syndrome.

Main Methods:

• Development of the AIM (anterior interosseous/median nerve) score, a latency ratio derived from stimulating the proximal median nerve.
• Simultaneous recording of evoked responses at the pronator quadratus and abductor pollicis brevis muscles.
• Testing on 100 normal nerves (61 patients) and patients with confirmed Kiloh Nevin syndrome, severe carpal tunnel syndrome, and borderline carpal tunnel syndrome.

Main Results:

• Normal nerves exhibited an average AIM score of 0.60 (SD = 0.06).
• Patients with Kiloh Nevin syndrome showed a significantly higher average AIM score of 0.76 (SD = 0.04).
• Patients with severe and borderline carpal tunnel syndrome presented with lower average AIM scores of 0.38 (SD = 0.06) and 0.48 (SD = 0.06), respectively.

Conclusions:

• The AIM score provides a reliable and easily performed electrodiagnostic method for diagnosing anterior interosseous nerve injuries.
• This technique demonstrates potential as a screening tool for carpal tunnel syndrome, particularly in complex cases.
• The latency ratio method offers a valuable advancement in the electrodiagnosis of peripheral nerve entrapment and compression injuries.