Respiratory function deterioration and the effect of non‐invasive mechanical ventilation in amyotrophic lateral sclerosis: the crucial importance of bulbar muscle involvement

Abstract

Non-invasive mechanical ventilation (NIV) is commonly suggested for patients with amyotrophic lateral sclerosis (ALS) [1]. Thus, identifying factors that are related to a rapid deterioration of respiratory function should be considered of critical importance. In line with this consideration, Leonardis et al. [2] evaluated the role of a series of respiratory parameters and subscores [ALSFunctional Rating Scale (ALSFRS-r), Norris scale (Norris-r)] as predictors of survival and indicators of NIV. We agree that the occurrence of respiratory symptoms and blood gas abnormalities can suggest a rapid progression to respiratory crisis, but we are surprised that bulbar onset of the disease has not adversely affected life-expectancy. In fact, it is well known that patients with bulbar-onset ALS tend to have respiratory symptoms that progress faster than patients with spinal-onset and are less likely to tolerate NIV. In particular, some studies have shown that the site of disease onset represents the main prognostic factor of survival time, and that bulbar involvement is accompanied by difficulties in adaptation to NIV [3,4]. The negative impact of bulbar muscle impairment on the prognosis of patients with ALS can be explained by the following observation: while the inspiratory and expiratory muscles can always be assisted or supported sufficiently to avert lung pathology, respiratory failure and tracheotomy for the cooperating patient, this is not the case for those with severe bulbar muscle dysfunction [5]. Therefore, advanced bulbar ALS patients should require intubation and tracheotomy tubes to prolong survival in acute settings [6]. In our opinion, the lack of negative effect of early bulbar muscle impairment on survival could be explained by the fact that the authors subjectively report the condition of ‘bulbar onset’ of the disease, but they fail to give a detailed definition of bulbar weakness or dysfunction, which can lead to a possible misdiagnosis of bulbar involvement. Disclosure of conflict of interest