Serum neurofilament light chain measurements following nerve trauma

Abstract

Background: Optimal functional recovery following peripheral nerve injuries (PNIs) is dependent upon early recognition and prompt referral to specialist centres for appropriate surgical intervention. Technologies which facilitate the early detection of PNI would allow faster referral rates and encourage improvements in patient outcomes. Serum Neurofilament light chain (NfL) measurements are cheaper to perform, easier to access and interpret than many conventional methods used for nerve injury diagnosis, such as electromyography and/or magnetic resonance imaging assessments, but changes in serum NfL levels following traumatic PNI have not been investigated. This pre-clinical study aimed to determine whether serum NfL levels can: (1) detect the presence of a nerve trauma and (2) delineate between different severities of nerve trauma.

Methods: A rat sciatic nerve crush and common peroneal nerve crush were implemented as controlled animal models of nerve injury. At 1-, 3-, 7- and 21-days post-injury, serum samples were retrieved for analysis using the SIMOA® NfL analyser kit. Nerve samples were also retrieved for histological analysis. Static sciatic index (SSI) was measured at regular time intervals following injury.

Results: Significant 45-fold and 20-fold increases in NfL serum levels were seen 1-day post-injury following sciatic and common peroneal nerve injury, respectively. This corresponded with an eightfold higher volume of axons injured in the sciatic compared to the common peroneal nerve (p < .001). SSI measurements post-injury revealed greater reduction in function in the sciatic crush group compared with the common peroneal crush group.

Conclusions: NfL serum measurements represent a promising method for detecting traumatic PNI and stratifying their severity. Clinical translation of these findings could provide a powerful tool to improve the surgical management of nerve-injured patients.

Keywords: biomarker; diagnosis; nerve crush; nerve injury; serum.

FIGURE 1

Serum concentration of neurofilament light chain (NfL) increases following nerve injury. NfL concentration was measured in serum samples retrieved from rats following surgical crush injury of the sciatic or common peroneal nerve (n = 5 animals for all data points except 21 days where n = 3). Data points represent the mean ± standard deviation. Dotted line indicates serum NfL concentration (0.05 ± 0.2 pg/mL) in uninjured control animals (n = 10). ***p < .001, **p < .001, mixed‐effects analysis with Sidak's multiple comparisons test comparing the two injury groups at each time point. ####p < .0001, ##p < .01, ANOVA with Tukey's multiple comparisons test comparing each injury group at each time point to baseline uninjured control.

FIGURE 2

Nerve injury models and volume of axons affected. Dashed lines represent the site of the crush. One red cube represents 0.3 mm³ volume of axons in (B) and 0.2 mm³ in (C) (calculated by measuring the total neurofilament positive area in a cross‐section of the stump immediately proximal to the crush site, multiplied by the length of the distal segment). Nerve segments shaded in red represent the length distal to the crush site that were measured to determine volume of axons that degenerated distal to the injury site. (A) Intact sciatic nerve with tibial and common peroneal branches shown. (B) Sciatic nerve crush (injury performed 5 mm distal to hip joint). (C) Common peroneal nerve crush (injury performed 5 mm distal to knee joint). The black arrows in the micrographs indicate neurofilament positive staining in (D) sciatic nerve cross‐section immediately proximal to the injury site and (E) common peroneal nerve cross‐section immediately proximal to the injury site. Volume of axons injured (F) was quantified using all of the injured sciatic nerves (n = 18) and injured common peroneal nerves (n = 18), ****p < .0001, Mann–Whitney test.

FIGURE 3

Static sciatic index (SSI) following rat sciatic and common peroneal nerve crush. SSI measurements were obtained at baseline then at various times following nerve crush. Mixed‐effects analysis indicated significant (p < .0001) effects of time, type of crush and interaction between the two factors. # compares each time point to Day 0 baseline in the same group, using Dunnett's post hoc test (# p < .05, ###p < .001, ####p < .0001). * compares sciatic to CP at each time point, using Sidak's multiple comparisons test (**p < .01, ****p < .0001).