Forced vital capacity deterioration in amyotrophic lateral sclerosis has an inflexion point

Serial evaluation of forced vital capacity (FVC) were performed in 34 patients with amyotrophic lateral sclerosis, 28 of whom were followed until death. Successive evaluation of FVC in the same patient did not show a linear progression. An inflexion point was detected in most patients followed to death (81%) with initial normal FVC values. The decline was more rapid and survival time was less than 1 year in most patients after the inflexion point. Significant changes in FVC were characteristic of the second half of the course of the disease. FVC results are useful for determining the presence and degree of respiratory system involvement, but our results suggest that FVC alone cannot serve as a quantitative test in clinical trials, since most patients show a curvilinear slope in FVC deterioration instead of a linear slope.