What are the typical ultrasound findings for leprosy nerve involvement?

Ultrasound Findings in Leprosy Nerve Involvement

High-resolution ultrasound is significantly more sensitive than clinical examination in detecting peripheral nerve thickening in leprosy and should be used as a primary diagnostic tool for evaluating leprosy neuropathy. 1

Key Ultrasound Findings in Leprosy Neuropathy

Nerve Enlargement

• Increased cross-sectional area (CSA) of peripheral nerves is the most consistent finding in leprosy, with specific thresholds for abnormal enlargement: >7.1 mm² for radial nerve, >8.17 mm² for ulnar nerve, >10.17 mm² for median nerve, >9.50 mm² for lateral popliteal nerve, and >11.21 mm² for posterior tibial nerve 1
• Nerve enlargement is detected by ultrasound in approximately 71% of leprosy patients, with an average of 3.6 enlarged nerves per patient 2
• Ultrasound detects nerve enlargement in significantly more nerves (47%) compared to clinical palpation (20%) (p<0.001) 1

Pattern of Nerve Involvement

• Asymmetric nerve enlargement is characteristic of leprosy neuropathy, with significant differences between corresponding nerves on opposite sides 2
• Regional and non-uniform thickening is common, with maximum enlargement typically occurring proximal to osteofibrous tunnels, particularly in ulnar and tibial nerves 2
• Ulnar and tibial nerves are most frequently affected in leprosy 2, 3

Echotexture Abnormalities

• Distorted nerve echotexture is a hallmark finding, showing loss of the normal fascicular pattern 3
• Hypoechoic areas within the nerve represent granulomatous infiltration or edema 3
• Significant correlation exists between abnormal nerve echotexture on ultrasound and clinical parameters of sensory loss and muscle weakness (p<0.001) 3

Vascularity Changes

• Increased neural vascularity detected by color Doppler imaging is present in approximately 26% of examined nerves in leprosy patients 3
• Hypervascularity is more common in patients experiencing type 1 or type 2 leprosy reactions 3
• Endoneural flow on Doppler correlates significantly with clinical parameters of nerve thickening and functional impairment (p<0.001) 3

Clinical Correlation with Ultrasound Findings

• Ultrasound detects nerve thickening in 71.4% of nerves with clinical function impairment and in 39.6% of nerves without any apparent clinical impairment 1
• The agreement between clinical palpation and ultrasound detection of nerve enlargement is poor (kappa = 0.30 overall), highlighting the superiority of ultrasound in detecting subclinical nerve involvement 3
• Nerve damage detected by ultrasound is more extensive and involves more nerves than clinically expected 3

Recommended Scanning Protocol

• A standardized scanning approach should include bilateral examination of ulnar, median, superficial radial, common fibular, and sural nerves at specific anatomical sites 4
• For each nerve, assessment should include measurement of cross-sectional area, evaluation of vascularity with color Doppler, and assessment of epineural thickness 4
• Patient positioning should follow standard musculoskeletal ultrasound guidelines with proper positioning for each nerve examination 5
• Transducer manipulation should be careful to avoid applying excessive pressure that may reduce the appearance of synovial hypertrophy or Doppler signal 5

Practical Considerations

• Hand-held portable ultrasound devices show strong correlation with standard ultrasound equipment (r = 0.76, p<0.001) in detecting nerve enlargement in leprosy, offering potential for use in resource-limited settings 6
• Multisegmental ultrasound approach (examining nerves at multiple points along their course) improves detection of the characteristic non-uniform, regional nerve thickening pattern in leprosy 2
• Ultrasound can help differentiate leprosy neuropathy from other demyelinating neuropathies by identifying the characteristic pattern of asymmetric, multifocal nerve enlargement 4

Common Pitfalls and Caveats

• Clinical examination alone is subjective and inaccurate for assessing nerve enlargement in leprosy patients 3
• Nerve enlargement may be present in all clinical forms of leprosy, highlighting the importance of ultrasound evaluation in all leprosy patients regardless of clinical classification 2
• Proper standardization of scanning technique and knowledge of normal nerve ultrasound appearance and measurements are essential for accurate interpretation 5
• Transducer frequency should be at least 10 MHz or higher for optimal visualization of peripheral nerves 1