Comparative Performance of Different Respiratory Test Parameters for Detection of Early Respiratory Insufficiency in Patients With ALS

Background and objectives: To compare the performance of different respiratory function testing parameters in a multidisciplinary amyotrophic lateral sclerosis (ALS) clinic.

Methods: Demographics, clinical data, and respiratory testing parameters were abstracted from the medical records of patients who attended a multidisciplinary ALS clinic from 2008 to 2016. We compared the performance of the 3 primary respiratory test parameters used by Medicare for the initiation of noninvasive ventilation (NIV) (forced vital capacity [FVC] < 50% predicted, maximum inspiratory pressure [MIP] < 60 cm H₂O, and abnormal overnight pulse oximetry [OvOx]) on how they related to several clinically relevant attributes.

Results: Four hundred seventy-six patients were identified who underwent at least 1 respiratory test. Abnormalities of OvOx, MIP, and FVC occurred at a median of 1.6, 1.5, and 3.8 years from disease onset, respectively (p < 0.00001). Patients with bulbar-onset ALS exhibited earlier abnormalities in MIP and FVC than in spinal-onset ALS (p < 0.005). The median survival after an abnormal OvOx, MIP, or FVC test was 1.4, 1.4, and 0.9 years, respectively (p < 0.0001). Using the ALS Functional Rating Score respiratory subscales, at the time of reported respiratory symptoms there were abnormalities in OvOx (60%), MIP (69%), and FVC (19%). Conversely, when respiratory parameter abnormalities preceded reported respiratory symptoms, this occurred with frequencies in OvOx (79%), MIP (42%), or FVC (24%). Four hundred forty-three patients (93.1%) developed at least 1 abnormal respiratory measure meeting Medicare criteria for NIV consideration, but fewer than 50% in our cohort demonstrated NIV use. Improved survival in subjects using NIV was statistically significant in patients with bulbar-onset ALS.

Discussion: Abnormalities in OvOx and MIP perform better than FVC at early detection of neuromuscular respiratory weakness in ALS. Initiation of NIV in patients with respiratory insufficiency may improve the overall survival in ALS. In the setting of the COVID-19 pandemic, FVC and MIP have not been routinely performed because of infectious aerosol generation. OvOx, which we now routinely mail to patients' homes, has been used exclusively during the COVID-19 pandemic and allows for continued remote monitoring of the respiratory status of patients with ALS.

Classification of evidence: This cohort study provides Class III evidence that in people with ALS, OvOx and MIP are valuable respiratory parameters for the detection of early respiratory insufficiency.