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Updated: Jul 17, 2026
Screening of Axonal Degeneration in Carpal Tunnel Syndrome Using Ultrasonography and Nerve Conduction Studies
Published on: January 11, 2019
Second lumbrical muscle recordings improve localization in severe carpal tunnel syndrome
Richard Brannegan1, Russell Bartt
1Division of Neurology, John H Stroger Hospital of Cook County, Chicago, IL 60612, USA. richard.brannegan@hektoen.org
Objective:
To determine how often the second lumbrical motor potential is present when the abductor pollicis brevis (APB) motor potential is absent in severe carpal tunnel syndrome (CTS).
Design:
Prospective study of consecutive patients with severe CTS and an absent motor potential from the APB.
Setting:
Single-center public hospital-based electromyography lab.
Participants:
Patients with a clinical diagnosis of CTS who had an absent median sensory response and an absent median motor response to APB on routine nerve conduction testing. Twenty-two hands of 19 patients were examined.
Interventions:
Not applicable.
Main Outcome Measure:
Presence and distal latency of motor potential to the second lumbrical.
Results:
The second lumbrical potential was present in 17 hands (77%). The distal motor latency to the second lumbrical was prolonged in all (mean, 9.1ms; normative value, <4.1ms).
Conclusions:
Second lumbrical recordings improve localization in many patients with severe CTS when routine median sensory and motor conduction studies produce no potentials.
