The BORG dyspnea score : a relevant clinical marker of inspiratory muscle weakness in Amyotrophic Lateral Sclerosis

The aim of the study was to determine whether the Borg dyspnea scale could be a useful and simple marker to predict respiratory muscle weakness in ALS. From April 1997 to 2001, respiratory function was perfomed in 72 patients together with the Borg score in both the upright (uBorg) and supine (sBorg) positions. Mean upright VC was 81 ± 24 % predicted, SNIP was 55 ± 26 % predicted, PImax was 57 ± 26 % predicted and PaCO2 was 41 ± 6 mmHg. The mean Borg scores in the upright and supine positions were 1.7 ± 1.5 and 2.2 ± 2, respectively. A significant relationship between SNIP and uBorg (r=0.4; p=0.0007) and SNIP and sBorg (r=0.58; p<0.0001) was observed. Upright VC, ∆VC, PImax and PaCO2 were significantly correlated with SNIP. A cutoff value of 3 on the sBorg scale provided the best sensitivity (80%) and specificity (78%) [AUC = 0.8] to predict a SNIP ≤40 cm H2O, indicating severe inspiratory muscle weakness. Patients with a sBorg score ≥3 also exhibited significantly lower VC, PImax, Pm,tw, and slightly higher PaCO2 (43.7 ± 7 vs. 39.2 ± 5 mmHg; p=0.05). The Borg dyspnea scale is a valuable non-invasive test to predict inspiratory muscle weakness in ALS patients. Amyotrophic lateral sclerosis (ALS) is a devastating and progressive neurodegenerative disorder of unknown etiology that affects both the upper and lower motor neuron pathways of the nervous system. Respiratory failure (resulting from progressive respiratory muscle weakness) is the usual cause of death [1, 2]. The degree of respiratory muscle involvement is considered difficult to quantify from respiratory symptoms alone. The vital capacity (VC) is the main parameter, used in clinical practice to appreciate indirectly respiratory muscle involvement, with the disadvantage of a poor sensitivity,. The supine position may aggravate symptoms (particularly dyspnea) and spirometry values such as VC (ref). Supine fall in VC was demonstrated to be a sensitive marker of diaphragmatic weakness [3, 4]. The presence of orthopnea was also found to be a marker of poor prognosis in ALS patients but its intensity was not quantified. The rate of decline of vital capacity (VC) is the standard method to evaluate the progression of respiratory involvement [5-7]. Both volitional tests (such as maximal inspiratory pressure (PImax), maximal expiratory pressure (PEmax) and sniff nasal inspiratory pressure (SNIP)) and patient-independent tests (such as twitch mouth pressure (Pm,tw) or trans-diaphragmatic pressure) can be used to assess respiratory muscle strength (RMS) more specifically [8-13]. Recently, Morgan et al. showed that SNIP is a valuable and simple non-invasive test to detect inspiratory muscle weakness with a high prognostic value in ALS [14]. Non-invasive positive pressure ventilation (NIPPV) has been shown to improve survival, slow the rate of decline of RMS and improve quality of life in ALS patients [15-18]. Current ALS practice guidelines suggest the monitoring of upright VC in order to detect declining respiratory function [6]. These guidelines concur with those of the American College of Chest Physicians, supporting the initiation of NIPPV at the onset of respiratory symptoms, or once a fall below 50% of predicted upright VC and/or a PaCO2 ≥45 mmHg and/or a PImax <60 cmH2O are documented [19]. Many of the aforementioned specific markers of respiratory muscle function are not readily available at the time of initial assessment of ALS patients by the neurologist. Careful evaluation of respiratory signs and symptoms is recommended in current guidelines on ALS management, as defined by the French consensus on ALS management [20]. Little is known about the clinical significance of available dyspnea scores in ALS, particularly regarding their ability to predict inspiratory muscle weakness. The aim of this study was therefore to evaluate the performance of the modified Borg scale [21] to detect respiratory muscle weakness in ALS patients.