Neck flexion weakness predicts respiratory dysfunction in amyotrophic lateral sclerosis

Objective: Neck flexion (NF) weakness is a frequently observed clinical feature in amyotrophic lateral sclerosis (ALS), particularly in advanced disease. The aim of the present study was to assess whether NF weakness could be a clinical biomarker for development of respiratory dysfunction. Methods: Sixty-two ALS patients were prospectively recruited at Brain and Nerve Research Center. Neck flexion strength was assessed by the Medical Research Council (MRC) score and handheld dynamometry (HHD). Respiratory function testing was assessed by spirometry, including forced vital capacity (FVC) and forced expiratory volume in 1 second (FEV1). Site of disease onset, disease duration, and ALSFRS-R were recorded. Results: Neck flexion weakness (MRC ≤4) was evident in 27% of ALS patients. There was a significant reduction of FVC in ALS patients with weak NF (ALS_NFweakness 70.0 ± 7.2%; ALS_NFnormal 86.8 ± 2.4% predicted, p = 0.038). Additionally, reduction of HHD measurements was significantly correlated with FVC (R = 0.487, p < 0.001) and FEV1 (R = 0.465, p < 0.001), and was most prominent in bulbar onset ALS (FVC: R² = 0.673, p = 0.002). Of relevance, the presence of NF weakness (MRC ≤ 4) was a significant predictor of reduced FVC ≤50% predicted (Chi² = 7.68, p = 0.006), a threshold indicating need for ventilatory support. Conclusion: Neck flexion weakness, particularly when quantified by the MRC score and HHD, serves as a marker of respiratory dysfunction in ALS patients. This simple clinical assessment may herald the development of respiratory dysfunction and requirement for respiratory ventilatory support.