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Related Experiment Video

Updated: Jan 7, 2026

Screening of Axonal Degeneration in Carpal Tunnel Syndrome Using Ultrasonography and Nerve Conduction Studies
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Thenar Muscle Atrophy: Clinical, Electrodiagnostic, and Ultrasound Features in 197 Patients.

Lisa B E Shields1, Vasudeva G Iyer2, Stephen Furmanek3

  • 1Norton Neuroscience Institute, Norton Healthcare, Louisville, KY 40202, USA.

Neurology International
|December 24, 2025
PubMed
Summary

Thenar muscle atrophy can stem from various causes, including carpal tunnel syndrome. Ultrasound (US) is crucial for diagnosis when electrodiagnostic (EDX) studies are inconclusive, especially in severe median nerve entrapment cases.

Keywords:
carpal tunnel syndromeelectrodiagnostic studymedian nerveneurologythenar muscle atrophyultrasound

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Area of Science:

  • Neurology
  • Diagnostic Imaging
  • Musculoskeletal Disorders

Background:

  • Thenar muscle atrophy, affecting the abductor pollicis brevis (APB), opponens pollicis (OP), and flexor pollicis brevis (FPB), is commonly linked to carpal tunnel syndrome (CTS).
  • Other potential causes include nerve injuries, neuropathies, plexopathies, radiculopathies, ventral horn cell disorders, disuse atrophy, and congenital aplasia.
  • Clinical assessment combined with electrodiagnostic (EDX) and ultrasound (US) studies aids in identifying the etiology of thenar atrophy.

Purpose of the Study:

  • To describe the clinical, electrodiagnostic (EDX), and ultrasound (US) findings in a large cohort of patients presenting with thenar muscle atrophy.
  • To evaluate the diagnostic utility of EDX and US in determining the cause of thenar atrophy.

Main Methods:

  • A retrospective review was conducted on 197 patients (226 hands) with thenar atrophy who underwent both EDX and US examinations.
  • Patients were classified based on clinical and US findings into those with total thenar atrophy (all three muscles) or partial thenar atrophy (one or two muscles).

Main Results:

  • Of 226 hands, 77.0% exhibited partial thenar atrophy, and 96.0% had sensory loss. Weakness of APB and OP muscles was observed in all hands.
  • EDX revealed severe median nerve entrapment at the carpal tunnel in 97.3% of hands. Sensory nerve action potentials (SNAPs) and compound muscle action potentials (CMAPs) of the APB were absent in 93.8% and 82.3% of hands, respectively.
  • US demonstrated hyperechoic APB and OP muscles in 99.6% of hands, with Heckmatt grade 3 (increased echogenicity, loss of architecture) in 67.3% of hands.

Conclusions:

  • Electrodiagnostic studies may not always definitively confirm carpal tunnel syndrome in cases of thenar atrophy due to absent SNAPs and CMAPs.
  • Ultrasound imaging is essential for confirming the cause of thenar atrophy, particularly when EDX findings are inconclusive or absent.
  • US findings, such as hyperechogenicity and altered muscle architecture, provide valuable diagnostic information for thenar muscle atrophy.