Diaphragmatic ultrasound: Prospects as a tool to assess respiratory muscle involvement in amyotrophic lateral sclerosis.

Abstract

Ultrasonography (USG) of the diaphragm is a promising alternative to pulmonary function tests (PFT) for assessing respiratory function in amyotrophic lateral sclerosis/motor neuron disease (ALS/MND). We studied 33 patients fulfilling Awaji criteria (definite=14; probable=12; possible=7) and 33 age and gender-matched controls. Diaphragm thickness was measured using USG at the end of expiration (DTex) and end of inspiration (DTin). The thickness ratio (TR) was calculated as DTin/DTex. The mean age at onset and duration were 49.73 ± 12.7 years and 13.57 ± 9.7months, respectively. Men=25 (75.8%); Limb onset ALS/MND=24 patients (72.7%); bulbar onset=9 (27.3%). Compared to controls, ALS/MND patients had reduced mean DTex (2.22 ± 0.29 mm vs. 2.02 ± 0.32 mm, p=.012) and DTin (4.0 ± 0.71 mm vs. 3.41 ± 0.38 mm, p < .001). PFTs done in 31 patients showed restrictive abnormality in 80.6%. Significant positive correlation was seen between percentage of predicted forced vital capacity (FVC%) and DTin (p=.009) and TR (p=.037) but not with DTex (p=.852). No significant correlation was seen between diaphragmatic thickness and other PFT parameters or ALSFRS scores. The diaphragmatic thickness showed a significant decrease in ALS/MND as compared to controls. End-inspiratory diaphragmatic thickness and TR correlated well with %FVC. Thus, diaphragmatic USG could be a potential alternative to PFTs in assessing respiratory function in ALS/MND patients having the advantage of less patient participation and ease of performing in late stages of ALS/MND.