Early assessment in bulbar-onset amyotrophic lateral sclerosis detects similar rates of nocturnal desaturation and orthopnoea compared to non-bulbar-onset disease

Background Pulmonary function measures are commonly used to determine timing of non-invasive ventilation (NIV) initiation in amyotrophic lateral sclerosis (ALS). However, these tests may be difficult to perform and unreliable in those with bulbar disease. We evaluated the rates of orthopnoea and nocturnal desaturation detected using nocturnal pulse oximetry (NPO), two key criteria for NIV initiation, separately in people with bulbar-onset and non-bulbar-onset ALS. Methods We conducted a retrospective analysis of 93 individuals with ALS undergoing three consecutive nights of NPO screening. Demographics, diurnal respiratory function measures and NPO data were compared. Nocturnal desaturation was defined as > 2% of total sleep time with oxygen saturation < 90%. Results Twenty-nine people had bulbar-onset ALS and 64 had non-bulbar-onset ALS. The prevalence of orthopnoea and the proportion with nocturnal desaturation were similar between bulbar-onset and non-bulbar-onset groups (24% vs. 20% and 76% vs. 67%, respectively). People with bulbar-onset ALS were older and underwent initial oximetry earlier in their disease trajectory following ALS-symptom onset than those with non-bulbar-onset ALS (67 +/- 10.5 vs. 61 +/- 11.9 years old, p = 0.02 and 17.5 (11.00-24.75) vs. 31.0 (18.00-63.50) months, p = 0.005, respectively). Conclusion People with bulbar-onset ALS were assessed with NPO sooner, but nocturnal desaturation was detected at similar rates to those with non-bulbar-onset ALS. Absence of orthopnoea and preserved lung function were poor indicators of nocturnal desaturation in both groups. Given the difficulties performing respiratory function tests in people with bulbar disease, early and regular NPO assessment in bulbar-onset ALS is warranted, even without symptoms.