136 Assessment of Peripheral Nerve Damage with a Myelin Specific MRI Method

Abstract

INTRODUCTION: Management of peripheral nerve injuries relies on patient history/exam and electromyography. Unfortunately, the determination of a successful repair can take months to years using these methods, which delays decision-making and increases the likelihood of permanent sensorimotor deficits. Therefore, new biomarkers that monitor nerve de/regeneration prior to muscle reinnervation may allow for earlier detection of failed repairs, earlier reoperations, and improved restoration of function. METHODS: Peripheral nerve MRI was performed at 3 Tesla in 4 subjects (27-60 y.o., two female). Bilateral thigh/knee MRI was performed in two subjects with chronic traumatic neuropathies to the peroneal or sciatic nerves, and bilateral elbow MRI was performed in two subjects five months after posterior interosseous or ulnar nerve decompression. MTR maps were estimated from high-resolution magnetization transfer-weighted and proton density-weighted images. MTR values were estimated in (i) regions immediately distal to the site of damage, (ii) proximal regions in the same nerves, and (iii) healthy contralateral nerves. Damaged nerves (i) were compared to proximal/healthy nerves (ii, iii) using a Wilcoxon rank-sum test. RESULTS: MRI was well tolerated and free of motion and fat artifacts. Furthermore, nerves were readily distinguished from surrounding fat and muscle in the high-resolution MTR maps. MTR values were significantly reduced distal to the injury site (23.6 ± 3.6%) relative to proximal regions in the same nerves (33.9 ± 6.0%, p = 0.03) and healthy contralateral nerves (37.3±3.8%, p = 0.03). CONCLUSION: MTR detects decreases in myelin related to nerve damage and, therefore, may be a viable biomarker of Wallerian degeneration. Subject enrollment in a larger longitudinal study is ongoing, which will allow us to determine if MTR values are responsive to regeneration and predictive of outcomes. We are also investigating novel methods with improved specificity in the presence of edema, which may confound MTR acutely after trauma.