Peripheral nerve imaging in amyotrophic lateral sclerosis

We systematically identified and reviewed 29 studies of peripheral nerve ultrasound or magnetic resonance imaging (MRN) in amyotrophic lateral sclerosis (ALS). The majority of the ultrasound studies reported smaller nerves and nerve roots in ALS compared to healthy controls, but there was a large overlap of the cross-sectional nerve area between ALS and controls. Most of the MRN studies confirmed nerve abnormalities demonstrating slight T2 hyperintensities and, sometimes, mild enlargement of more proximal nerve segments (plexus, roots) in ALS. The size of the proximal nerve segments, i.e. nerve roots, is thus somewhat incongruent between nerve ultrasound and MRN in ALS. Peripheral nerve ultrasound has the potential to differentiate between ALS and multifocal motor neuropathy (MMN) in that patients with MMN have significantly larger nerves. Conversely, there is an overlap of MRN abnormalities in ALS and MMN, restricting the techniques' utility in the clinical setting. A subgroup of patients with ALS seems to reveal a sonographic nerve pattern suggesting peripheral nerve inflammation. In the future, combined imaging with nerve ultrasound and MRN assessing parameters such as blood flow or textural markers may aid in the understanding of the deep nerve microstructure down to the fascicle level, and thus, in the classification of the nerve state as more degenerative or more inflammatory in ALS. This systematic review provides evidence that nerve imaging abnormalities are common in ALS.