Respiratory function in amyotrophic lateral sclerosis patients. The role of sleep studies

Respiratory function decline in association with sleep breathing abnormalities in Amyotrophic Lateral Sclerosis (ALS) patients are fully recognized as crucial manifestations in the natural course of the disease, severely affecting the prognosis. The aim of this study was to evaluate the respiratory function at daytime and during sleep in a population of ALS patients and investigate the necessity of sleep study performance for the appropriate management of the disease.

Twenty eight (10 male, 18 female) unselected patients with ALS, were evaluated in terms with their functional status by means of the ALS Functional Scale (ALSFSC). Baseline anthropometric measurements, pulmonary function tests and arterial blood gases analysis were performed, as well as evaluation of patients' perception of dyspnoea. A polysomnography was performed using a multichannel ambulatory recording.

Nineteen patients had sleep disordered breathing with an RDI (Respiratory Disorder Index)>5/h (from 5.6/h to 83/h) and 10 patients had an RDI>15/h. All patients had impaired functional capacity by the ALSFSC and 11 patients (39.3%) reported mild to moderate dyspnoea. FVC was below 80% predictive value in 22 patients and in 8 patients hypoxaemia (PaO2<80 mmHg) and in 12 patients hypercapnia (PaCO2>40 mmHg) was present. There was no correlation found between spirometric values, maximum inspiratory and expiratory pressures and sleep study parameters. There was a significant correlation between PaCO2 and RDI (r=0.498, p<0.01), and PaO2 with nocturnal hypoxaemia (average SpO2, r=0.436,p<0.05).

Sleep-breathing abnormality is common in ALS patients even in the absence of documented respiratory failure. Clinical evaluation and respiratory function tests alone may not be sufficient to predict sleep disordered breathing (SDB) and nocturnal breathing assessment should be included in the evaluation of respiratory function.