- Acquired central hypoventilation syndrome (ACHS) is a rare, life-threatening disorder in which the brain loses its ability to generate or regulate automatic breathing, most prominently during sleep.
- In healthy individuals, respiratory drive is controlled by brainstem centers that respond to changes in blood oxygen and carbon dioxide levels, ensuring continuous rhythmic ventilation. In ACHS, this automatic control is impaired due to damage to the central nervous system, resulting in inadequate or absent ventilatory effort, particularly when voluntary breathing mechanisms are reduced, such as during non-REM sleep. The condition differs from obstructive sleep apnea or neuromuscular disorders because the problem lies in central respiratory drive, not in airway obstruction or respiratory muscle weakness.
- The syndrome is termed “acquired” to distinguish it from congenital central hypoventilation syndrome (CCHS), which is caused by PHOX2B gene mutations. In ACHS, the impairment develops after birth, usually as a result of structural or functional injury to the brainstem. Reported causes include traumatic brain injury, ischemic or hemorrhagic stroke involving the medulla, posterior fossa or brainstem tumors, infections such as encephalitis or poliomyelitis, demyelinating disorders like multiple sclerosis, and neurodegenerative diseases. Iatrogenic cases have also been described, such as following neurosurgery involving the medullary or pontine regions. Depending on the extent of the injury, the hypoventilation may range from occurring only during sleep to persisting even during wakefulness.
- Clinically, ACHS presents with episodes of apnea, cyanosis, and shallow or absent breathing during sleep, often leading to hypoxemia and hypercapnia. Patients may also experience morning headaches, daytime somnolence, confusion, or cognitive impairment due to chronic carbon dioxide retention. In severe cases, hypoventilation extends into wakefulness, with a high risk of sudden cardiorespiratory collapse. Unlike obstructive forms of sleep-disordered breathing, polysomnography in ACHS shows apneas or hypoventilation with a complete absence of respiratory effort rather than obstructive airflow limitation.
- Diagnosis is based on a combination of clinical features, polysomnography, arterial blood gas analysis, and neuroimaging. Sleep studies confirm central hypoventilation by documenting reduced or absent ventilatory effort. Blood gases reveal sustained hypercapnia and hypoxemia, especially at night. Neuroimaging, such as MRI or CT, often identifies the underlying lesion in the brainstem or central respiratory pathways. Other neuromuscular or pulmonary causes of hypoventilation must be carefully excluded to confirm ACHS.
- Management of ACHS centers on ensuring adequate ventilation and oxygenation. Most patients require mechanical ventilatory support during sleep, either through non-invasive positive-pressure ventilation or tracheostomy-based invasive ventilation in severe cases. In selected patients, diaphragmatic or phrenic nerve pacing can provide a more physiologic alternative, enabling independence from continuous mechanical ventilation. Treating the underlying cause (such as surgical removal of a tumor, antiviral therapy, or rehabilitation after trauma) is essential, although full recovery of automatic breathing is uncommon. Long-term monitoring is required to prevent complications from chronic hypoxemia, hypercapnia, and nocturnal respiratory events.
- In summary, acquired central hypoventilation syndrome is a disorder of impaired brainstem respiratory control that arises from injury or disease of the central nervous system. It is defined by inadequate automatic breathing, especially during sleep, leading to hypoxemia and hypercapnia in the absence of primary lung or muscle disease. Unlike congenital forms caused by PHOX2B mutations, ACHS develops later in life due to trauma, stroke, tumors, infections, or degenerative conditions. Diagnosis requires sleep studies, blood gases, and neuroimaging, while management relies on ventilatory support and treatment of underlying causes. Prognosis depends on the severity of the lesion and the ability to maintain adequate long-term respiratory support, but the condition carries significant morbidity and mortality if unrecognized.
