Amyotrophic lateral sclerosis (ALS) is a relentlessly progressive, presently incurable, neurodegenerative disorder that causes muscle weakness, disability, and eventually death. The ALS Functional Rating Scale (ALSFRS-R) is a validated rating instrument for monitoring the progression of disability in patients with ALS. The ALSFRS-R incorporates questions for the assessment of dyspnoea, orthopnea, and the need for ventilatory support. However, studies on the relationship of ALSFRS-R with objective measurements of respiratory function are scanty. Therefore, we set out to investigate the relationship of ALSFRS-R with respiratory function indices in ALS patients.

We studied 33 consecutive, ambulatory, Caucasian patients (21 men) with ALS. Seventeen patients had bulbar involvement. Two patients did not satisfactorily perform the lung function testing and they were excluded. ALSFRS-R was assessed. Routine lung function tests, maximum static expiratory (Pemax) and inspiratory (Pimax) mouth pressures were measured. Respiratory muscle strength (RMS) was also calculated.

ALSFRS-R (mean±SD) was 35 ± 9. Patients had: age, y=60 ± 10, FEV₁,%pred=83 ± 18, FVC,% pred=86 ± 20, TLC,% pred=94 ± 11, and DL_CO,% pred=92 ± 18. Pemax,% pred was 80 ± 28, Pimax,% pred was 73 ± 31, and RMS,% pred was 77 ± 27. These pressures were below the normal limits in 15, 20, and 17 patients, respectively. ALSFRS-R was significantly correlated with Pemax%pred, RMS%pred, and FEV₁/FIV₁ (r = 0.46, p < 0.01; r = 0.38, p = 0.035; n = 20, r=-0.71, p < 0.001, respectively).

In conclusion, FEV₁/FIV₁ index has a good correlation with ALSFRS-R (n = 20, r=-0.71, p < 0.001, FEV₁/FIV₁ = 1.630 - [0.018 * ALSFRS-R] ± 0.165).