In ALS, what is the primary cause of death?

• A. Respiratory paralysis reaching the diaphragm
• B. Myocardial infarction
• C. Renal failure
• D. Bacterial pneumonia unrelated to respiratory failure

Answer: (A)

The main idea is that death in ALS most often comes from respiratory failure due to weakness of the breathing muscles, especially the diaphragm. As motor neurons degenerate, the diaphragm and other inspiratory and expiratory muscles lose strength, making it hard to ventilate adequately and exchange gases. When ventilation collapses, CO2 rises and oxygen falls, leading to respiratory failure—the direct, terminal event. Infections like pneumonia can occur as a consequence of prolonged respiratory impairment and immobility, but they typically follow the failure of breathing rather than being the initiating cause. Other organ problems such as heart attack or kidney failure aren’t the characteristic primary death drivers in ALS.