2025 Workshop Handout Bundle-W18A Basic NMUS Penry

W18A Basic NMUS Penry
Pdf Summary
This comprehensive review, prepared by experts from Wake Forest University School of Medicine and presented at the 2025 AANEM Annual Meeting, details neuromuscular ultrasound (NMUS) basics and its application in entrapment neuropathies. NMUS is a safe, noninvasive imaging technique complementing electrodiagnostic studies by visualizing peripheral nerves, muscles, and surrounding structures with high resolution.

Key practical aspects covered include:

- <strong>Ultrasound Technique and Equipment:</strong> Use of linear array transducers, typically high frequency (12-18 MHz), either a small "hockey stick" or a wider probe, optimizing image quality by adjusting gel application, probe positioning, focal zones, depth, and gain. Proper handling and cleaning protocols ensure safety and image fidelity. Real-time imaging and video capture enhance dynamic assessments, such as nerve movement and muscle fasciculations.

- <strong>Imaging and Measurement of Muscles:</strong> Muscle appears with characteristic striated patterns; pathology like atrophy and fibrosis increases echogenicity (brightness). Accurate muscle thickness measurements require minimal probe pressure with attention to anatomical landmarks. Muscle echogenicity is influenced by anisotropy and scan angle, so consistent technique is vital for comparison. Fasciculations can be detected and may aid ALS diagnosis.

- <strong>Nerve Imaging and Assessment:</strong> Normal nerves display a honeycomb fascicular pattern in cross section. The primary diagnostic parameter is cross-sectional area (CSA), measured by tracing the inner hyperechoic rim. Enlargement and hypoechogenicity signal pathology. Nerves can be followed longitudinally to locate maximal enlargement. Power Doppler may reveal increased intraneural vascularity in pathological states.

- <strong>Applications in Common Entrapment Neuropathies:</strong> 
   - <em>Carpal Tunnel Syndrome (CTS):</em> Median nerve enlargement proximal to the wrist (CSA >10-12 mm²) and decreased nerve mobility are common ultrasound findings. Anatomical variants (bifid nerve, persistent median artery) may influence diagnosis and treatment.
   - <em>Ulnar Neuropathy at the Elbow:</em> Nerve enlargement at the cubital tunnel with a maximal CSA around 9-10 mm² is typical; dynamic imaging can assess nerve subluxation/dislocation.
   - <em>Ulnar Neuropathy at the Wrist:</em> Less common; often caused by anatomical lesions like ganglion cysts or thrombosed arteries.
   - <em>Fibular Neuropathy at the Knee:</em> Most common lower extremity entrapment; nerve CSA upper limit ~20 mm². Identification of intraneural ganglion cysts (seen in ~18% cases) is critical as they guide surgical management.

- <strong>Clinical Integration and Reporting:</strong> NMUS findings should be combined with clinical and electrodiagnostic data for comprehensive interpretation. Reports should include which nerves and muscles were imaged, CSA measurements, echogenicity, vascularity, and nerve mobility. Image storage and accessibility facilitate review and auditing.

This review underscores neuromuscular ultrasound's growing role in diagnosing entrapment neuropathies and neuromuscular diseases. Its ability to provide dynamic, anatomical, and pathological information enhances clinical care, with a learning curve best approached by mastering common nerves and muscles progressively. As technology advances and user expertise grows, NMUS is expected to become increasingly integral in neuromuscular evaluation and management.
Keywords
Neuromuscular ultrasound
Entrapment neuropathies
Carpal tunnel syndrome
CTS
Ulnar neuropathy
Fibular neuropathy
Cross-sectional area measurement
Muscle echogenicity
Nerve imaging
Dynamic ultrasound assessment
Electrodiagnostic studies