P37. Various sonographic gray-scale measures of the peripheral nerve differ between ALS and ALS disease mimics

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Background We aimed to examine whether distinct sonographic gray-scale measures of the peripheral nerve vary between amyotrophic lateral sclerosis (ALS), ALS disease mimics and various neuropathies to ascertain the diagnostic value of high-resolution ultrasound for the differentiation of these disorders. Methods Our analysis comprised n = 54 controls and n = 250 patients (ALS n = 169, hereditary spastic paraplegia [HSP] n = 25 [pure and complex], primary lateral sclerosis [PLS] n = 13, immune-mediated neuropathies [IMNs] n = 12, hereditary demyelinating neuropathies [HDNs] n = 13, hereditary axonal/mixed neuropathies [HMNs] n = 13, hereditary neuropathy with liability to pressure palsy [HNPP] n = 5). Peripheral nerve ultrasound was conducted and offline analysis of median and ulnar nerve segments, each considered as a region of interest (ROI), comprised the calculation of the nerves’ cross sectional area (CSA), median echo intensity (EI), echo variance (EV), fascicular portion (hypoechoic fraction [HF]) and textural correlation (TCOR). As there were no side differences, left- and right-sided measures were averaged. General linear models were conducted to assess group effects on various sonographic measures (significant at p Results Sonographic measures depended on age, sex, height and weight. At entrapment and non-entrapment sites IMNs and HDNs revealed nerve enlargement compared to the remainder, while in HDNs compared to IMNs nerve CSA was even greater (2fold vs. 3fold enlargement compared to controls). In hereditary neuropathies (HDNs, HMNs) median nerve EI was lowest, which was accompanied by high EV, fascicular enlargement (high HF) and alterations of the nerves’ texture (TCOR). In ALS (all subtypes) versus the remainder comprising HSP, PLS and IMNs, ulnar nerve CSA was smaller; moreover, in ALS compared to HSP or axonal/mixed neuropathies (HMNs) the median nerves’ texture pattern (TCOR) was different. In HNPP compared to the remaining groups (except IMNs and HDNs) wrist median nerve CSA (entrapment site) was greater, which was related to fascicular enlargement (high HF). Results remained unchanged after model adjustment for age, sex, height and weight. Conclusion ALS, ALS disease mimics and various neuropathies are not only characterized by distinct sonographic nerve areas, but also reveal in-between-group differences of further sonographic gray-scale nerve measures. Future studies need to address the question how sonographic composite scores could aid in the differentiation between ALS and its disease mimics and how those scores relate to further ultrasound features such as the nerves’ microvascular blood flow.