Disclosures: Carter M. Newey, DO: No financial relationships or conflicts of interest

Case Diagnosis: A 54-year-old male with a full-thickness extensor pollicis longus tear

Case Description: A 54-year-old male was referred for electrodiagnostic testing to assess for radial neuropathy after acute onset of left thumb and wrist extensor weakness, with pain and intermittent paresthesia of dorsal left hand, following heavy work with a saw. Physical exam showed edema and tenderness at the posterior wrist, pain in the proximal posterior forearm and inability to extend the left thumb. There was pain inhibition with extension of the wrist and other digits, but no clear weakness.

Setting: Outpatient clinicAssessment/

Results: MRI of the hand performed at an outside facility reported no tendon pathology, raising the clinical concern for a radial neuropathy. An electrodiagnostic evaluation was performed and showed no evidence of radial neuropathy. High frequency ultrasound was performed and revealed a retracted extensor pollicis longus tendon tear at the level of the first MCP joint, and superficial radial nerve irritation at the distal tendon stump. It also showed a normal appearance of the deep branch of the radial nerve and normal radial-innervated muscle echotexture.

Discussion: In this case, the false-negative MRI result created diagnostic confusion. Ultrasound provides advantages of high resolution and dynamic imaging. Also, it is often performed in a “point-of-care” setting that facilitates extension of the imaging field when needed. The combination of electrodiagnosis and ultrasound provided compelling evidence of normal function of the deep branch of the radial nerve and the superficial branch sensory symptoms were related to compression from the tendon tear.

Conclusion: This case demonstrates the value of combining the physiologic information provided by electrodiagnosis with the anatomic information from ultrasound to distinguish an extensor tendon tear from an incomplete radial neuropathy. This supports the value of using these diagnostic modalities in combination when presented with potential musculoskeletal mimics.

Level of Evidence: Level V

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PM&R Meeting Abstracts - https://pmrjabstracts.org/abstract/high-frequency-ultrasound-evaluation-of-an-extensor-pollicis-longus-rupture-in-a-suspected-radial-neuropathy-a-case-report/