Objective:

To investigate the frequency, electrodiagnostic associations, and prognostic significance of paradoxical thinning of the diaphragm on ultrasound.

Background:

Point-of-care ultrasound of the diaphragm is increasingly utilized and highly sensitive and specific in detection of neuromuscular diaphragmatic weakness. In a subset of patients with neuromuscular diaphragmatic weakness, paradoxical thinning of the diaphragm during inspiration is observed on ultrasound; however, its significance is uncertain.

Design/Methods:

Records of patients presenting to two EMG laboratories (Mayo Clinic, Rochester, MN, and University of Alberta, Edmonton, AB) from 01/01/2022-12/31/2022, to evaluate suspected neuromuscular diaphragmatic weakness, were reviewed. 

Results:

214 patients were referred and 19 patients excluded due to incomplete information. Of 195 patients (384 hemidiaphragms), 104 had phrenic neuropathy, 12 had myopathy, and 79 had no evidence of neuromuscular disease affecting the diaphragm. Diaphragm ultrasound was 93% sensitive and 99% specific in diagnosis of neuromuscular diaphragmatic weakness, utilizing final clinical diagnosis as reference standard. Paradoxical thinning of the diaphragm occurred in 31 (27%) patients with neuromuscular disease involving the diaphragm and was unilateral in 30. There was no significant difference in phrenic NCS or diaphragm EMG results in patients with neuromuscular diaphragmatic weakness and paradoxical thinning versus without. Most patients (71%) with paradoxical thinning required non-invasive ventilation (NIV), the majority unilateral (83%) with normal contralateral ultrasound. Paradoxical thinning and BMI≥30 or greater in patients with neuromuscular diaphragmatic weakness were independent risk factors for requiring NIV in multivariable logistic regression analysis, with odds ratios of 2.887 (95% CI:1.166, 7.151) and 2.561 (95% CI: 1.186, 5.532), respectively.

Conclusions:

Paradoxical thinning of the diaphragm with inspiration occurs in patients with prominent diaphragm weakness. This is most common with phrenic neuropathy and is a significant independent risk factor for requiring NIV. Unilateral paradoxical thinning is alone sufficient for needing NIV. BMI≥30 additionally confers increased risk of requiring NIV in patients with neuromuscular diaphragmatic weakness.