Do bulbar-onset amyotrophic lateral sclerosis patients have an earlier respiratory involvement than spinal-onset amyotrophic lateral sclerosis patients?

AIM: Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease involving limbs and bulbar muscles. The major cause of death in these patients is respiratory insufficiency. However, bulbar-onset ALS patients have a shorter survival than those with spinal-onset. It is not established if this difference is related to an earlier respiratory dysfunction in bulbar-onset patients. The aim of the present study was to determine if bulbar-onset patients have an earlier respiratory impairment as compared with the spinal-onset ones.
METHODS: From the population of ALS patients followed in our centre, we studied 82 patients (45 spinal-onset and 37 bulbar-onset, group 1 and 2 respectively), all evaluated between 6-18 months after disease onset. We investigated forced vital capacity, maximal inspiratory (PI max) and expiratory (PE max) pressures, mouth occlusion pressure at 100 ms after inspiration, arterial blood gases, percutaneous nocturnal oxymetry, phrenic nerve conduction, needle electromyography (EMG) of the right diaphragm and right internal intercostals muscles and functional ALS scale (ALS-FRS).
RESULTS: No statistical difference was found for gender and disease duration between both groups, but bulbar-onset patients were older. PI max and PE max were statistically lower (P<0.001 and P<0.006, respectively) in group 2. However, no correlation was found between bulbar ALS-FRS subscore and PI max or PE max.
CONCLUSIONS: Our results support that PI max and PE max are sensitive measurements of respiratory dysfunction in bulbar patients. Probably, this finding cannot be solely explained by the oro-facial weakness of bulbar-patients. We speculate that respiratory accessory muscles weakness can contribute for this observation.