Utility of phrenic nerve ultrasound in amyotrophic lateral sclerosis

Abstract

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder affecting the upper and lower motor neurons causing progressive weakness. It eventually involves the diaphragm which leads to respiratory paralysis and subsequently death. Phrenic nerve (PN) conduction studies and diaphragm ultrasound has been studied and correlated with pulmonary function tests in ALS patients. However, PN ultrasonography has not been employed in ALS. This study aims to sonographically evaluate the morphologic appearance of the PN of ALS patients. Thirty-eight ALS patients and 28 normal controls referred to the neurophysiology laboratory of two institutions were retrospectively included in the study. Baseline demographic and clinical variables such as disease duration, ALS Functional Rating Scale-Revised score, and ALS region of onset were collected. Ultrasound was used to evaluate the PN cross-sectional area (CSA) of ALS and control subjects. The mean PN CSA of ALS patients were 1.08 ± 0.39 mm on the right and 1.02 ± 0.34 mm on the left. The PN CSA of ALS patients were significantly decreased compared to controls (p value < 0.00001). The PN CSA of ALS patients was not correlated to any of the demographic and clinical parameters tested. This study demonstrates that ALS patients have a smaller PN size compared to controls using ultrasonography.

Ultrasound imaging of the phrenic nerve at the scalene muscle level

“…[17] Similar to other studies, our study showed no significant correlation between the PN CSA and the demographic data. [14][15][16][17] One important challenge in some cases was distinguishing the PN from the C5 root. In these cases, caudal manipulation was used in order to separate both structures and identify the PN passing from lateral to medial over the anterior scalene muscle.…”

Ultrasonic detection of vagus, accessory, and phrenic nerve atrophy in amyotrophic lateral sclerosis: Relation to impairment and mortality

“…Present measures of PN CSA are lower than values reported earlier for ALS patients and normal population [8]. This can well be explained by the method applied here with separate measuring of the long and short axis diameter and consecutive calculation of the elliptic CSA [25].…”

“…The resulting decrease of calibers of cervical nerve roots and of peripheral motor nerves in ALS patients as compared to healthy individuals can be detected with high-resolution ultrasound [3][4][5][6][7]. Recently it was demonstrated using ultrasound that also phrenic nerve (PN) calibers are decreased in ALS [8]. However, the functional relevance of PN atrophy in ALS patients is unclear so far.…”

Morphological study of the phrenic nerve to determine a reference value for the myelinated fiber density in elderly individuals

“…Suratos et al reported that the right side of the PN tended to have a larger cross-sectional area than the left side in 28 normal control cases. 19 A left-right difference would be significant from an anatomical point of view; however, a histological study of 35 formalin-fixed human cadavers reported no significant left-right differences in PN surface area and myelination area. 20 The cross-sectional area in ultrasonography is considered equivalent to the endoneurial area histologically; thus, data regarding left-right PN differences appear to be contradictory.…”

“…Suratos et al . reported that the right side of the PN tended to have a larger cross‐sectional area than the left side in 28 normal control cases 19 . A left–right difference would be significant from an anatomical point of view; however, a histological study of 35 formalin‐fixed human cadavers reported no significant left–right differences in PN surface area and myelination area 20 .…”