4. Median/ulnar nerve ultrasound cross-sectional area ratio in ALS

Publication date: April 2018
Source:Clinical Neurophysiology, Volume 129, Issue 4
Author(s): Jun Tsugawa, Yu-ichi Noto, Thanuja Dharmadasa, Nidhi Garg, Matthew C. Kiernan
BackgroundIt has been shown that hand muscle wasting in amyotrophic lateral sclerosis (ALS) preferentially affects the thenar muscles, with relative sparing of the hypothenar muscles. This so-called "split-hand" is clinical sign that can be used to differentiate ALS from mimic disorders, and is thought to be caused by a difference in nerve excitability between median and ulnar nerve. The split-hand phenomenon has been largely discussed in regard to neurophysiological finding, but no studies performed comparing median and ulnar nerve size using ultrasound. We therefore sought to compare nerve size between the median and ulnar nerves in ALS using ultrasound in order to determine whether this may give further insight into the split-hand phenomenon.ObjectiveTo identify whether nerve ultrasound results might reflect the clinical split-hand sign in ALS patients and whether these findings can be used to differentiate ALS from other neuromuscular disorders.MethodsUltrasound was used to image both the median and ulnar nerves of 98 patients with ALS and 82 patients with other neuromuscular disorders (non-ALS). The nerve cross-sectional area (CSA) was measured at the wrist, the forearm, and the upper arm bilaterally. Nerve CSA values and median/ulnar nerve CSA ratios were compared at different locations between the two groups.ResultBoth the median and ulnar nerve CSA values were smaller in the ALS group than in the non-ALS group, except for the median nerve at the wrist. The median/ulnar nerve CSA ratio was comparatively decreased in the upper arm segment. There was a significant difference between the two groups at the wrist on the left side and at upper arm on the right side (Left wrist (IQR) ALS: 2.00 (1.67,2.33) vs non-ALS: 1.63 (1.35,2.18) p = 0.003, Right upper arm (IQR) ALS: 1.29 (1.12,1.50) vs non-ALS: 1.37 (1.16,1.69) p = 0.003).ConclusionWe observed that the median/ulnar nerve CSA ratio was decreased in ALS patient at the upper arm segment. Overall, these findings suggest that there is preferential involvement of the median nerve compared to the ulnar nerve in ALS, which is consistent with the clinical findings of the split hand in these patients. This adds further support to the involvement of peripheral mechanisms underlying this phenomenon. Therefore, ultrasound may be a useful non-invasive tool to objectively detecting changes. Further studies assessing cortical contribution to the clinical and ultrasound findings are warranted to elucidate this pathology further.



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