[Pathophysiology of respiratory insufficiency in neuromuscular diseases]

In end stage neuromuscular disease respiratory muscle fatigue can lead to respiratory failure. There is no close correlation between the degree of peripheral muscle weakness and the weakness of the respiratory muscles. Early in the disease the maximum in- and expiratory pressures can be abnormal even though the results of spirometry are normal. Progressive weakness of the respiratory muscles results in a decrease in vital capacity and eventually in alveolar hypoventilation, especially during sleep. General muscle weakness and fatigue may be the reasons why sleep hypoventilation is often overlooked in its early stages. Dyspnea may be a early symptom but it is not unusual that alveolar hypoventilation remains undetected until complications ensue (Cor pulmonale, polycythemia, altered alertness).