The terminal latency of the phrenic nerve correlates with respiratory symptoms in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a rapidly progressing neurodegenerative disease that involves limb, axial, bulbar, and respiratory muscles.(Haverkamp et al., 1995) Weakness and fatigue of the respiratory muscles eventually induce respiratory insufficiency, which is the main cause of death in this disease.(Haverkamp et al., 1995) Since respiratory function is an important factor influencing the survival of patients with ALS,(Lechtzin et al., 2001; Lechtzin et al., 2007) its assessment is essential for monitoring disease progression and determining the timing for non-invasive ventilation that is proven to increase the survival and quality of life of patients with ALS.(Bourke et al., 2006; Andersen et al., 2007) Generally, forced vital capacity (FVC) has been suggested to be a prognostic factor for ALS.(Fallat et al., 1979; Czaplinski et al., 2006) In patients with ALS with bulbar symptoms, however, respiratory function tests, such as FVC, are not always reliable in practice; these patients have weak lip seal that impairs the accurate evaluation of their respiratory function.(Pinto et al., 2009) Moreover, assessment of respiratory function depends on cooperation, which is difficult to obtain in patients who are less motivated, depressed, or have behavioral changes as commonly observed in patients with ALS.(Phukan et al., 2007)

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