Pulmonary function in patients with amyotrophic lateral sclerosis at disease onset

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disorder affecting both the upper and lower motor neurons. Deteriorating pulmonary function as a reflection of progressive respiratory muscle weakness is a common feature, accounting for the majority of deaths. The aim of the study was to describe a trend in initial pulmonary function tests (PFT) of amyotrophic lateral sclerosis (ALS) patients, in addition, differentiating between the types of disease onset, bulbar, limb muscle, and a combination.

Initial PFT were gathered from 32 consecutive patients in our clinic with the diagnosis of ALS, they were categorized by the type of disease onset. Values obtained were referenced to the 95% confidence limits for normality.

There was evidence of significant reductions in both the FEV1 (64.7% predicted) and FVC (61.2%), with preservation of the FEV1/FVC (81.7%). The MVV was significantly reduced (43%). Total lung capacity was 93.2%, the residual volumes was increased at 145.7%. Subgroup analysis failed to show significant differences between types of disease onset. In the bulbar onset group (versus the limb group) there was a trend for the MVV to be further reduced (p = 0.15) and the RV to be higher (157.4% versus 135.9%, P = 0.24).

ALS is a devastating disease that invariably leads to respiratory failure. Abnormal spirometric variables such as the FVC and MVV, likely reflect inspiratory muscle weakness and increased RV likely reflect expiratory muscle weakness. The type of disease onset did not result in a different pattern of PFT abnormalities.