High-resolution sonography: a new technique to detect nerve damage in leprosy

Abstract

Background: Leprosy is the most common treatable peripheral nerve disorder worldwide with periods of acute neuritis leading to functional impairment of limbs, ulcer formation and stigmatizing deformities. Since the hallmarks of leprosy are nerve enlargement and inflammation, we used high-resolution sonography (US) and color Doppler (CD) imaging to demonstrate nerve enlargement and inflammation.

Methodology/principal findings: [corrected] We performed bilateral US of the ulnar (UN), median (MN), lateral popliteal (LP) and posterior tibial (PT) nerves in 20 leprosy patients and compared this with the clinical findings in these patients and with the sonographic findings in 30 healthy Indian controls. The nerves were significantly thicker in the leprosy patients as compared to healthy controls (p<0.0001 for each nerve). The two patients without nerve enlargements did not have a type 1 or type 2 reaction or signs of neuritis. The kappa for clinical palpation and nerve enlargement by sonography was 0.30 for all examined nerves (0.32 for UN, 0.41 for PN and 0.13 for LP). Increased neural vascularity by CD imaging was present in 39 of 152 examined nerves (26%). Increased vascularity was observed in multiple nerves in 6 of 12 patients with type 1 reaction and in 3 of 4 patients with type 2 reaction. Significant correlation was observed between clinical parameters of grade of thickening, sensory loss and muscle weakness and US abnormalities of nerve echotexture, endoneural flow and cross-sectional area (p<0.001).

Conclusions/significance: We conclude that clinical examination of enlarged nerves in leprosy patients is subjective and inaccurate, whereas sonography provides an objective measure of nerve damage by showing increased vascularity, distorted echotexture and enlargement. This damage is sonographically more extensive and includes more nerves than clinically expected.

Figure 1. Ultrasonography and color Doppler images of peripheral nerves of healthy subjects.

A Transverse scan of medial nerve from a healthy subject as denoted by dotted ellipse (CSA = 4.5 mm²) showing hypoechoic fascicles separated by hyperechoic areas in a ‘honeycomb’ like pattern with absence of blood flow signals; B longitudinal ultra sonogram of ulnar nerve from a healthy subject (arrows) with hyperechogenic bands in a linear pattern appearing as bundles of straw.

Figure 2. Comparison of mean cross-sectional areas (CSA in mm²) in nerves from leprosy patients as compared to healthy control subjects.

The mean CSA in mm²±SD as determined by ultrasonography from 20 leprosy patients (L, open triangle) showed highly significant increase (p<0.0001, Mann Whitney) as compared to 30 healthy control subjects (H, open circle) for ulnar, median, lateral popliteal (LPN) and posterior tibial nerves (PTN). There was a wider scatter in the diseased nerves as compared to healthy controls.

Figure 3. Ultrasonography and color Doppler images of peripheral nerves of leprosy patients.

A transverse scan of an enlarged ulnar nerve indicated by an asterisk (CSA = 45 mm²) from BT leprosy patient with type 1 reaction showing no endoneural blood flow signals; B colour Doppler image of a right ulnar nerve in a BT patient (CSA = 51 mm²) undergoing type 1 leprosy reaction, showing increased endoneural and perineural blood flow signals (demarcated by solid arrow in a rectangular box, dashed arrow in a box shows a blood vessels) suggestive of acute neuritis; C colour Doppler image of a median nerve (shown by solid arrow) in a BT patient (CSA = 9 mm²) undergoing type 1 leprosy reaction with persistent artery (shown by dashed arrow), showing no endoneural flow signal.