Chest
Volume 103, Issue 2, February 1993, Pages 508-513
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Pulmonary Function at Diagnosis of Amyotrophic Lateral Sclerosis: Rate of Deterioration

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The purpose of this study was to determine the degree of respiratory muscle impairment in patients with newly diagnosed amyotrophic lateral sclerosis (ALS) and the subsequent rate of decline of respiratory function. Thirty-one of 36 patients had respiratory muscle weakness at presentation, although only 7 complained of any respiratory symptoms. Vital capacity (percent predicted) was significantly lower in the symptomatic group (55.9 ±20.3) compared with the asymptomatic group (76.4 ±21.0). Respiratory muscle impairment as measured by vital capacity (percent predicted) was related to stage of disease at presentation. Rate of decline of respiratory muscle strength as measured by VC (—3.5 percent/month), negative inspiratory pressure (NIF) (+2.9 cm H2O/month), and positive expiratory pressure (PEP) (—3.4 cm H2O/month) tended to be linear with a great deal of interpatient variability. It is concluded that early measurement of respiratory muscle strength in ALS with subsequent follow-up studies may be useful in determining overall prognosis and in decision making.

Section snippets

METHODS

Records were reviewed of all ALS patients under our care over a 10-year period ending December 1991. Criteria used for the diagnosis of ALS were described previously.3 In brief, a combination of upper and lower motor neuron dysfunction was required. Those patients in whom pulmonary function studies, including vital capacity (VC), maximum negative inspiratory pressure (NIF), and maximum positive expiratory pressure (PEP), were available from the time of diagnosis are included in this report.

RESULTS

Records of 49 patients with ALS were reviewed. Four were in respiratory failure at the time of presentation and required mechanical ventilation before any pulmonary function tests were performed. Nine did not have pulmonary function studies at the time of diagnosis. Thirty-six (stages at presentation ranging from I to IV) had pulmonary function studies available at the time of diagnosis. Of the latter group, 24 had sequential pulmonary function studies available for analysis over a period of

DISCUSSION

The natural history of ALS is a relentless progression of increasing weakness of all skeletal muscles, including the muscles of respiration, with eventual respiratory failure and death.1, 2 Amyotrophic lateral sclerosis will occasionally go undiagnosed until after the onset of respiratory insufficiency,3, 6 as occurred in 4 of the 49 patients (8.2 percent) reviewed herein. It is much more common, however, for patients to present with limb or bulbar symptoms without any complaints of respiratory

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Manuscript received February 14; revision accepted June30.

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