Clinical manifestations

Presentation and course

Congenital central alveolar hypoventilation syndrome is a rare genetic condition, which generally presents in the first year of life, although later presentations are reported (59; 19). Typically, the newborn presents with respiratory distress, shallow breathing, and cyanosis and requires mechanical ventilation and transfer to an intensive care unit. Abnormal blood gases with hypercapnia are a hallmark for this condition. Elimination of other causes of abnormal breathing, such as sepsis, cardiac malformation, seizure disorder, and neuromuscular disease is important. Congenital central hypoventilation syndrome is a dysfunction of the autonomic control of breathing, and the diagnosis may be confirmed by abnormal responses to hypercapnic challenge during sleep as noted in polysomnography, and the syndrome is definitively identified by genetic testing for PHOX2B mutation (35).

The spectrum of clinical presentation of congenital central alveolar hypoventilation syndrome is broad. Mild hypoventilation and shallow breathing during quiet sleep accompanying normal ventilation during wakefulness may be seen. In more severe cases, children demonstrate severe apneas and hypoventilation during sleep and various degrees of hypoventilation during wakefulness, with the development of serious respiratory acidosis due to a partially or completely absent response to hypercapnia and hypoxemia. Autonomic and brainstem dysfunction are often found. Rarely, infants may present with a syndrome of Hirschsprung disease and/or neuroblastoma before the subsequent development of respiratory issues (14).

The previous clinical criteria for diagnosing congenital central hypoventilation syndrome included (1) persistent hypoventilation during quiet (non-REM) sleep with PaCO2 greater than 60 mmHg; (2) symptoms during the first year of life; and (3) an absence of lung, cardiac, or neuromuscular disease (02). The 2010 revised recommendations now also require PHOX2B gene mutation to confirm the diagnosis of congenital central alveolar hypoventilation syndrome (03). Additionally, genetic testing of parents with affected children is also recommended.

Congenital central alveolar hypoventilation may occur in association with the following disorders:

A variant of central hypoventilation, known as late-onset central hypoventilation syndrome, presents in previously healthy children and has features similar to congenital central alveolar hypoventilation. These children, adolescents, and adults typically present with milder disease but can have many of the same features. These patients may have shallow breathing and more obvious hypoventilation in sleep with symptoms of morning headache and sleepiness. These patients also may have aberrant control of glucose, bradycardia, gastrointestinal dysmotility, pupillary abnormalities, and dysautonomia including temperature dysregulation (06). Respiratory failure is usually precipitated following a respiratory tract infection, administration of an anesthetic or a hypnotic, or by adenotonsillar hypertrophy. These patients may also have greater likelihood of having neural crest tumors.

Idiopathic central alveolar hypoventilation occurs as a result of reduced ventilation, which leads to nocturnal hypercapnia and hypoxemia. Unlike congenital central hypoventilation syndrome patients, who, when properly ventilated at night, do not have sleep abnormalities, patients with idiopathic central alveolar hypoventilation typically exhibit sleep fragmentation (insomnia with frequent arousals and wake episodes) and lighter stages of sleep (07). Daytime symptoms include hypersomnolence, morning headaches, peripheral edema, polycythemia, and cor pulmonale, with abnormal pulmonary function tests.

Comparatively, the acquired form of central alveolar hypoventilation is typically caused by a structural lesion, which leads to the loss of control of automatic respiration. It occurs in all ages and may result from asphyxia, central nervous system infection, trauma, tumor, cerebral infarction, or intracranial hemorrhage. Following recovery from coma, hypercapnia is noted, sometimes along with brainstem lesions identifiable on MRI. The acquired form may be most evident in obese, middle-aged subjects, with an estimated prevalence of 0.3% in the general population (75).

Patients have an attenuated sense of breathlessness following exercise, particularly underwater swimming. The condition often becomes apparent after acute respiratory failure requiring intubation followed by carbon dioxide retention or difficulty weaning from the ventilator and can be unmasked in the setting of standard administration of sedatives.

Numerous case reports of association with other disorders or other acquired forms are described:

Prognosis and complications

In the case of congenital central hypoventilation syndrome, morbidity and mortality are related to timely diagnosis and referral to an experienced pediatric center. Serious complications include cardiac arrhythmias, lethargy, respiratory arrest, and, most seriously, death during sleep. The prognosis is generally worse in patients with Hirschsprung disease, ganglioneuroma, or neuroblastoma. Prolonged survival and an overall good quality of life are possible today, and with earlier recognition of the syndrome, serious complications can be avoided.

Children and adolescents with congenital central hypoventilation syndrome may also have developmental and cognitive problems that require special attention. Studies have demonstrated problems in attention, working memory, processing speed, perceptual reasoning, visuographic skills, and executive functions, resulting in issues with interpersonal communication and daily living skills in this population (117; 121). In a study comparing congenital central hypoventilation syndrome patients to their parents, the children scored significantly below their parents in indices of intelligence, vocabulary, and abstraction, as well as below population normative data for IQ, reasoning, processing speed, and working memory (120). Measures of neurocognitive function may already be reduced in preschool-age children (17).

Clinical vignette

A full-term infant born by cesarean section to non-consanguineous parents underwent further evaluation when he did not pass meconium in the first 24 hours of life. Work-up revealed signs of intestinal obstruction and prompted colonic biopsy that showed findings consistent with Hirschsprung disease. The patient was intubated and sedated for an ileostomy and successfully discharged home afterwards.

However, at four weeks of life, he was noted to develop unusual pauses in breathing while sleeping, which prompted readmission to the hospital. Further work-up revealed that the patient was having oxygen desaturations associated with these pauses in breathing. Arterial blood gas analysis revealed a compensated respiratory acidosis. He was intubated and ventilated. A diagnosis of congenital central hypoventilation syndrome was suspected and prompted PHOX2B mutation analysis. This revealed a heterozygous non-polyalanine repeat (NPARM) mutation. After discussion with family regarding the diagnosis of congenital central hypoventilation syndrome, the family agreed to placement of a tracheostomy.

Further review of family history revealed that the patient’s maternal uncle had also had Hirschsprung disease and died of a neuroblastoma at four years of age. The patient’s mother denied any history of sleep disturbance. She underwent genetic testing for PHOX2B mutation and was found to have the same NPARM mutation. Empiric evaluation of the patient’s mother’s sleep revealed mild central sleep apnea. The patient’s grandparents also underwent genetic testing, and the grandfather was found to also be heterozygous for the same mutation carried by his daughter and grandson.

This case is a modified version of a case reported by Low and colleagues in Pediatric Pulmonology (63). As discussed in this article, NPARM mutations account for roughly 10% of PHOX2B mutations and usually result in more severe, syndromic manifestations of the disease, as in this patient’s case—presenting with Haddad syndrome. However, this case also speaks to the variable penetrance of this mutation given a lack of symptoms in both the grandfather and the patient’s mother.

Biological basis

Etiology and pathogenesis

Genetics. Congenital central hypoventilation syndrome is most often due to heterozygous mutations of the gene encoding paired-like homeobox 2b, PHOX2B, a transcription factor that maps to chromosome 4p12. PHOX2B is expressed in both the central and the peripheral autonomic nervous system during human embryonic development. It is believed to be involved in early neural crest cell migration with a central role in the generation of normal respiratory patterning and autonomic function. It is also the predisposing gene for occurrence of neuroblastoma in different mutational patterns, ganglioglioma, and Hirschsprung disease.

Function. Phox2b expression in the brainstem respiratory network is preferentially associated with neurons involved in chemosensory integration, specifically by a chain of neurons involved in the integration of peripheral and central chemoreception. Studies in Phox2b transgenic mice suggest that hypercapnic ventilatory response impairment in congenital central hypoventilation syndrome may be related to Phox2B-expressing neuronal loss or maldevelopment in the nucleus tractus solitarius and retrotrapezoid nucleus, which are important centers of respiratory chemoreception and control (42; 34).

PHOX2B mutations disrupt breathing automaticity during sleep without causing major impairment of respiration during waking (98).

Genotype-phenotype correlations. Heterozygous mutations in PHOX2B were found in individuals with congenital central hypoventilation syndrome, with at least 90% of PHOX2B gene mutations consisting of abnormal alanine expansions within a 20-repeat polyalanine expansion tract in exon 3 resulting from (GCN)n triplet repeat expansions (50). In a Japanese cohort of 92 subjects, 86 had polyalanine repeat mutations (PARMs) and six had nonpolyalanine repeat mutations (NPARMs). Of the subjects with PARMs, it was noted that all subjects with 26 or more repeats presented with hypoventilation at birth. Those with 25 or fewer repeats had hypoventilation at variable timepoints or not at all (94). As such, the association of increased number of repeats with more severe respiratory presentation has been suggested, though rare cases of delayed/adult presentations in individuals with more than six additional repeats suggest incomplete penetrance through a multitude of gene-gene interactions (51). Comparatively, NPARMs comprise less than 10% of PHOX2B mutations and are known to produce more severe disruption of PHOX2B function, usually presenting as a syndrome associated with Hirschsprung aganglionosis and/or neurocristopathies (50).

Other associated genes. Increased prevalence of ventilatory dependence, Hirschsprung disease, and neural crest tumors were seen more frequently in the NPARM group as compared to those with polyalanine repeat mutations (14). Other mutations have been described in association with the congenital central hypoventilation syndrome phenotype, including genes involved in migration of neural crest origin, as well as genes upstream and downstream of Phox2b in biological pathways such as RET, GDNF, EDNRB, EDN3, LBX1, and MYO1H (32; 44). The involvement of multiple genes suggests that the genetic involvement has a complex pattern of inheritance.

Pathophysiology. The primary factors controlling breathing are arterial carbon dioxide via brain tissue pH. Alveolar ventilation is principally a function of carbon dioxide, as oxygen tension is normally maintained at levels higher than those that induce stimulation of the breathing system. Ventilatory responses to hypercapnia and to hypoxia help to maintain normal arterial blood gas tension (100). Peripheral chemoreceptors mediate responses to hypoxia, whereas central chemoreceptors mediate responses to carbon dioxide (via hydrogen ion concentrations). The central chemoreceptors are thought to be located near the surface of the fourth ventricle on the ventral side of the medulla oblongata, rostral and medial to the hypoglossal roots. Normally, progressive hypercapnia induces a linear increase in minute ventilation, whereas progressive hypoxia induces a hyperbolic increase. If a defect impairs the sensory system for monitoring carbon dioxide levels, ventilation is affected, particularly when sleep results in the loss of "wake stimuli" and volitional breath control, which facilitate control of ventilation during wake (31).

In patients with congenital central alveolar hypoventilation syndrome, exposure to 100% oxygen results in further hypoventilation compared to baseline, suggesting that the peripheral chemoreceptors are functional. The extent of hypoventilation is also state dependent, being maximal during deep NREM sleep with relatively normal gas exchange during REM (93). During wakefulness, children with congenital central alveolar hypoventilation have absent rebreathing ventilatory responses to hypoxia and hypercapnia. During exercise, children with congenital central alveolar hypoventilation may become hypoxic and hypercapnic; they increase their minute ventilation primarily by an increase in respiratory rate rather than by tidal volume. Further, minute ventilation does not match carbon dioxide production.

Neuroimaging and structural correlates. Structural and functional imaging with MRI indicates abnormalities in both the forebrain and the brainstem (84). Whether these changes contribute to the pathogenesis or are a result of tissue hypoxia is unclear. Postmortem analysis of neonatal lethal cases has shown loss of neurons in the locus coeruleus. This is mirrored in abnormal development of the locus coeruleus in a transgenic mouse model of the same PHOX2B mutation (78). Although radiological evaluations of the brain have failed to identify a lesion to account for the clinical and physiological features, a functional MRI compared activity at baseline and at two minutes of hypoxic challenge (15% oxygen, 85% nitrogen) in congenital central hypoventilation syndrome patients compared to controls. Results showed significant differences in the magnitude and timing of responses between the two groups indicative of deficient neurovascular activation in response to hypoxia (late or none) in congenital central hypoventilation syndrome patients, specifically in the posterior thalamic, cerebellar, midbrain, and limbic structures (65). These findings partially explain the absent perception of air hunger and lack of discomfort in patients with congenital central hypoventilation syndrome.

Association of congenital central hypoventilation syndrome with the occurrence of Hirschsprung disease, congenital neuroblastoma, ganglioneuroblastoma, and benign ganglioneuroma suggests that the primary defect relates to neural crest cell migration and function. Vagal hyperresponsiveness, sinus pauses, bradyarrhythmia, and an attenuated response to endogenous sympathetic stimulation suggest a diffuse alteration in autonomic nervous system function (79). In line with this hypothesis is the finding that autonomic nervous system dysfunction was more common in relatives of the patients with the syndrome compared to control subjects (116).

Comparatively, idiopathic alveolar hypoventilation syndrome is not associated with structural lesions and does not appear to have an identifiable etiology.

Epidemiology

Congenital, idiopathic, and acquired forms of central alveolar hypoventilation are rare. According to the French Congenital Central Hypoventilation Syndrome Registry, in 2005 the incidence was estimated to be 1 per 200,000 live births in France with an overall mortality rate of 38%, and a median age of death of three months (105). The median age of diagnosis was 3.5 months prior to 1995, but it has improved to less than two weeks in recent years. In a 2005 analysis of 43 patients in the French Congenital Central Hypoventilation Syndrome Registry, individuals had a mean age of 9 years (range 2 months to 27 years), 16% had Hirschsprung disease, and 31 (91%) of the 34 genetically tested individuals were heterozygous for PHOX2B mutations (105). An estimate of the minimum incidence of congenital central hypoventilation syndrome in Japan was calculated to be an average 1 per 148,000 births for years 2008 to 2013 (94), possibly due to increased awareness of the condition.

Prevention

No means of prevention are known for congenital or idiopathic central alveolar hypoventilation. However, early recognition of the disease and associated risk factors can expedite interventions and possibly preserve neurocognitive function. Case reports of mother-daughter transmission, siblings, and twins with congenital central hypoventilation syndrome suggest that genetic counseling of parents and siblings is appropriate after identification of individuals with congenital central hypoventilation syndrome. This is particularly relevant given the association noted between sudden infant death syndrome (SIDS) and PHOX2B polyalanine length variants in certain populations (60). There are cases reported of severe adverse events, including coma and death, related to alcohol use in adolescents and young adults with congenital central hypoventilation. Patients should be advised to abstain from alcohol or other substances that are known to cause respiratory suppression (18). One of the more serious yet preventable complications of central hypoventilation syndrome is cardiac autonomic dysregulation, which can lead to sudden death (40). Early cardiac workup and prediction for the need of a pacemaker is crucial. When genetic testing reveals PHOX2B mutations in asymptomatic adult family members, these patients should be followed longitudinally for the development of respiratory and cardiac disturbances (50).

Differential diagnosis

Confusing conditions

The infant presenting with apnea or respiratory failure must have other more common etiologies rigorously excluded, including sepsis, pulmonary infections, cardiopulmonary and neurologic malformations, intoxication, trauma, and neuromuscular disease. Conditions in childhood that can be easily confusing include rapid onset obesity, hypoventilation hypothalamic dysfunction and autonomic dysregulation (ROHHAD), and Prader-Willi syndrome and demonstrate hypoventilation relatively early in the course (10). Other conditions to consider include familial dysautonomia, Leigh syndrome, Chiari malformation type 1 and type 2, and achondroplasia.

In the adult with unexplained respiratory failure and inability to wean from mechanical ventilation, the differential diagnosis includes obstructive and restrictive lung disease, severe ventilation-perfusion mismatch associated with pulmonary emboli or other causes, respiratory muscle weakness or fatigue, neuromuscular disease, and toxins affecting neuromuscular or central nervous system function. Adults with nocturnal hypoxemia or hypercapnia should also be considered for other disorders, such as obstructive sleep apnea syndrome, central sleep apnea syndrome, and obesity hypoventilation syndrome.

Associated or underlying disorders

Rarely, the congenital form of central alveolar hypoventilation is associated with neurocristopathies including Hirschsprung disease and malignancies of crest cell origin, including congenital neuroblastoma, ganglioneuroblastoma, and benign ganglioneuroma. As a result of involvement of neural crest cells, dysautonomia – vagal hyperresponsiveness, sinus pauses, bradyarrhythmia, and/or an attenuated response to endogenous sympathetic stimulation – is frequently present, even in individuals who may not have significant respiratory symptoms (79; 58).

Lesions anywhere along the pathway from the chemoreceptive centers in the medulla, through the high cervical spine, to the phrenic nerves can result in an acquired form of central alveolar hypoventilation. As such, various disorders have been associated with the acquired form: vascular (medullary infarct, cervical anterior spinal artery syndrome, cerebral venous thrombosis), inflammatory/immunologic (neurosarcoidosis, multiple sclerosis, anti-Hu and Zic4 paraneoplastic antibodies), infectious (meningitis), traumatic (cordotomy, anatomic brainstem compression), oncologic (metastatic), and neurodegenerative (progressive supranuclear palsy).

Diagnostic workup

According to consensus of the American Thoracic Society published in 1999, the diagnosis of congenital central alveolar hypoventilation syndrome required monitoring during sleep without mechanical ventilation. The 2010 American Thoracic Society policy statement concluded that suspected congenital central alveolar hypoventilation syndrome diagnosis is confirmed by demonstrating a PHOX2B gene mutation by sequential testing starting with a screening test that, if negative, should be followed by the sequel PHOX2B sequencing test in cases of high clinical suspicion (115). This statement also specifies other testing and diagnostic thresholds of such testing. These include tests to rule out other etiologies of hypoventilation: chest x-ray or computed tomography (CT) scan, neurologic evaluation including MRI and consideration of muscle biopsy, and echocardiogram. These tests are described further below.

Cardiopulmonary evaluation. Electrocardiogram, echocardiogram, Holter monitoring, and chest x-ray or CT may be indicated to rule out autonomic dysfunction, right heart failure, pulmonary hypertension, and primary lung disease. In one retrospective study, congenital heart disease was found in 30% of patients with molecularly confirmed congenital central hypoventilation syndrome, primarily manifesting as anomalies of the proximal aortic arch and proximal coronary arteries (62). Furthermore, in a retrospective chart review of 72 congenital central alveolar hypoventilation patients, 22% (16) had evidence of potential life-threatening cardiac arrhythmias, most of which had significant sinus pauses on ambulatory monitoring without necessarily manifesting symptoms of syncope, dizziness, chest pain, tingling in the left arm, or palpitations (58).

Imaging studies. MRI of the brain should be performed to evaluate for intracranial lesions. The acquired forms are associated with intracranial hemorrhage, ischemic stroke, or tonsillar herniation. If Hirschsprung disease is suspected, MRI of the spine is indicated as well to evaluate the patient for ganglioneuromas.

Neurologic evaluation searching for hypotonia and neuromuscular disorders. Testing involves nerve conduction studies and electromyography. Muscle biopsy to look for myopathic disorders and pupillometry to assess for autonomic dysfunction may have a role as well (85). If diaphragmatic paresis is suspected, physicians should perform diaphragmatic fluoroscopy and ultrasound. If Hirschsprung disease is present, barium enema will show bowel distention, and colon biopsy will demonstrate an aganglionic colon.

Metabolic and mitochondrial disease screening. Late-onset congenital central hypoventilation syndrome in children may present with nonspecific signs, including cardiopulmonary compromise, autonomic dysregulation, and hypotonia, and it can masquerade as a metabolic syndrome (eg, Leigh disease, pyruvate dehydrogenase deficiency, and carnitine deficiency) (89). In the early stages of evaluation, consultation with a medical geneticist may be helpful.

Genetic workup. Clinical diagnostic testing for congenital central hypoventilation syndrome involves targeted mutation analysis or sequence analysis. Polyacrylamide gel electrophoresis PHOX2B screening testing is an appropriate first-line investigation. If negative in the setting of suspected congenital central alveolar hypoventilation syndrome, the sequel PHOX2B sequencing test should be performed (48). More information can be accessed at the following site: www.genetests.org.

It is recommended that a sleep study be performed at the time of initial work-up (09), followed by every 3 to 4 months until 5 to 6 years of age. Annual evaluation after 6 years of age is adequate, provided the patient is stable (39), as the patients require assisted ventilation throughout their lifetime.

Evaluation of patients with suspected idiopathic central hypoventilation. For adults presenting with unexplained (idiopathic) hypoventilation or hypoxemia infectious, cardiac, pulmonary, and neuromuscular causes must be excluded. Patients with idiopathic alveolar hypoventilation syndrome show evidence of abnormal pulmonary function with formal testing, as well as polycythemia, chronic hypoxemia, and hypercapnia, and it has been suggested that an elevated serum bicarbonate level may be of diagnostic value (69). If a mutation of PHOX2B is identified in a child, gene mutations should be systematically examined in any biological adult relative with unexplained central hypoventilation, and all, even apparently healthy, biological parents in order to determine if they harbor a somatic mosaic (108). One report indicates the possibility of germline mosaicism for PHOX2B mutations in parents, emphasizing the importance of screening subsequent pregnancies in families with a child that has congenital central hypoventilation syndrome (88). Adults who present with reduced cardiac baroreflex and blunted sympathetic mediated response should be suspected of having the adult-onset type of central alveolar hypoventilation (25). Polysomnography often demonstrates periods with reduced tidal volumes lasting several minutes along with sustained hypoxemia, which tends to worsen during REM sleep. Hypercapnia occurs during episodes of hypoventilation, due to a decreased minute ventilation. Polysomnography with the monitoring of blood gases by arterial catheter will typically demonstrate central apneas with hypercapnia that is greatest in NREM sleep, less pronounced in REM sleep, and least apparent during wakefulness. Apnea duration may increase at the end of the night, reflecting further blunting by sleep fragmentation of already abnormal arousal responses.

Management

The goal of treatment is to ensure adequate ventilation, particularly during sleep, as these metabolic perturbations, especially in congenital central alveolar hypoventilation syndrome, have neurocognitive sequelae (119). These patients frequently face multiple medical issues that require a coordinated multidisciplinary approach including pulmonologist, otolaryngologist, gastroenterologist, cardiologist, neurologist, sleep medicine physician, geneticist, respiratory therapist, psychologist, and social work (52). Initially, some of these patients can be improved with noninvasive ventilation techniques, whereas other may require intubation and mechanical ventilation.

Available options for long-term mechanical ventilation include noninvasive positive airway pressure (PAP) ventilation with bilevel positive airway pressure in the spontaneous/timed mode (S/T) or intelligent volume-assured pressured support (iVAPS), phrenic nerve/diaphragmatic pacing, negative pressure ventilation by body chamber, and tracheostomy (20; 54). Chronic mechanical ventilation dependence is the norm.

If central alveolar hypoventilation is a problem only during sleep, nasal ventilation is suitable. In infants with this disorder, early use of noninvasive positive pressure (nasal bilevel positive airway pressure) decreases complications caused by prolonged artificial ventilation or tracheostomy (73). However, in two infants, bilevel positive airway pressure (with spontaneous/timed mode) failed to provide suitable ventilation and tracheostomy was performed; therefore, application of bilevel positive airway pressure for patients younger than five years might not be the general norm of treatment (21). Newer modes of invasive or noninvasive support, such as average volume-assured pressure support, may be tried for comfort or changing needs of individual children as they age (110). Ventilation during sleep must be assessed regularly, and an apnea-heart rate alarm should be used.

Preparation should be made for a trial of a negative pressure chamber to avoid potential complications of pseudoprognathism or midface hypoplasia, which are commonly associated with prolonged use of nasal masks for noninvasive positive pressure ventilation in children (NPPV). Negative pressure ventilators of the cuirass or poncho type may be used additively with bilevel positive airway pressure to prevent upper airway closure due to negative pressure suction initiated by the ventilator and the lack of coordination between ventilator and upper airway muscle contractions. One study found that homecare support is beneficial for children needing mechanical ventilation, and it represents a valid alternative to long hospitalization for children with stable chronic respiratory failure (81).

Tracheostomy for children carries risks of morbidity and mortality and is associated with complications such as speech and swallowing impairments and infections of the upper airway. Eventual transition from this invasive form of ventilation to NPPV is possible during childhood with a proposed stepwise approach being put forward on how to make the transition (83). If tolerated, tracheostomies should be capped during the day and attached to a ventilator with humidified air at night. Despite the complications associated with tracheostomy, one study of the neurocognitive function of 88 children with congenital central alveolar hypoventilation syndrome over the age of 6 suggested that early (younger than 3 months of age) tracheostomy was associated with higher cognitive function than delayed (older than 3 months of age) tracheostomy or NPPV (80).

If ventilation is inadequate during both wakefulness and sleep, diaphragmatic pacing is a practical alternative once the patient is ambulating. There is a potential for obstructive apnea to occur if pacing results in decannulation of tracheostomy; however, this can be mitigated by optimizing stimulator amplitude in response to polysomnographic findings (76; 114). Evaluation of enlarged tonsils and adenoids is essential to determine if removal is required in the context of obstructive sleep apnea. Occasionally, bilateral pacing is usually required, especially in infants and young children with congenital central hypoventilation syndrome, and it may be successfully implemented in children as young as 9 months of age (26). In a small cohort (N=23) of individuals implanted at a variety of ages and followed for up to 30 years, phrenic nerve pacing afforded independence from tracheostomy and noninvasive ventilation (109). An alarm and regular assessment of the integrity of the system are required to prevent unexpected respiratory failure (13). Complications include destruction of the phrenic nerve, inability to pace the nerve at the time of surgery, infection and dehiscence of the surgical site, and breakage of the electrode wire. Malfunction of any part of the equipment may also occur, with failure of the receiver expected about 4 to 5 years after placement. Although technical problems are substantial, a survey of 150 subjects using diaphragmatic pacing found that 64% lived at home, 23% were in a hospital, 13% were in rehabilitation, and less than 5% were in nursing homes (36).

Consideration should be given to social surroundings, family support, bed partner, age, life expectancy, and financial situation. The initiation and follow up of nocturnal noninvasive positive airway pressure support for stable alveolar hypoventilation syndromes have previously been reviewed (11). Although the condition is serious, it can be controlled with prospects for optimal daytime performance, employment, and social life. Patients can be transitioned from one device to another in order to obtain optimal management (for example, from bilevel positive airway pressure to negative chamber ventilation or phrenic nerve pacing), but transition may be challenging if the child is younger than seven years of age (102). It is important to remember that families need support with these therapies, as frequently parents and caregivers have disturbed sleep (30).

Although congenital central hypoventilation syndrome is classically a chronic and permanent condition, cases have been reported in which clinical improvement or remission was possible. Clinical improvement with medroxyprogesterone in a patient with a right-sided pontomedullary stroke has been described (96). Two children with congenital central alveolar hypoventilation syndrome were successfully weaned off of mechanical ventilation with exogenous medroxyprogesterone (74). Another case report describes recovery of chemosensitivity to carbon dioxide in a woman with congenital central alveolar hypoventilation syndrome associated with desogestrel, a potent oral contraceptive (99). This relationship was further investigated in a mouse model, which suggested that desogestrel may improve resting ventilation in congenital central hypoventilation syndrome patients by stimulating baseline respiratory frequency, a known physiologic effect of progesterones (49). In addition to restoring a degree CO2 chemoresponsiveness, gonane progestins appear to increase the basal respiratory drive (61). That being said, pharmacologic management is unlikely to be sufficient for most patients who ultimately require ventilatory assistance, at least during sleep. It has also been noted that the antiepileptic medication carbamazepine improved daytime apneic episodes in a single patient but had no overt effect on sleep-related hypoventilation (91).

Despite varying courses and severities between patients, life-long follow-up is recommended. Cardiac monitoring should be performed to surveil for the emergence of abnormalities, particularly sinus pauses (107). One patient, who already utilized a diaphragmatic pacer, was successfully treated by the implantation of a dual chamber pacemaker for arrhythmias (56). No device-device interaction was noted in another patient with cardiac and diaphragmatic pacemakers for congenital central hypoventilation (76). Routine pulse oximetry, end-tidal carbon dioxide levels, and frequent checks of the ventilatory system chosen are essential to ensure continued efficacy.

Finally, children with congenital central hypoventilation syndrome may experience progressive worsening of social cognition and executive function, and therefore, close monitoring of developmental milestones and serial neurocognitive evaluation, paired with early intervention, should be considered (27).

Outcomes

Over the last few decades this disorder has evolved from one of high neonatal mortality to a less severe or diverse array of phenotypes that are being recognized later in life in both primary, genetic cases as well as in association with precipitating CNS pathology. Despite some pharmacologic agents bearing benefits for ventilation (eg, carbamazepine and desogestrel), there is currently no cure for the condition. The mainstays of treatment are lifetime assisted ventilation and multidisciplinary care. However, with carefully coordinated care and safety precautions most individuals are able to live reasonably normal lives, given that the main focus of treatment is resolution of sleep-predominant inadequate sleep drive through invasive and noninvasive ventilatory support or neurostimulation. In a 15-year review of 30 patients with congenital central hypoventilation syndrome, Fain showed that patients can have good long-term outcomes with early diagnosis and strategies to optimize assisted ventilation (28). In their cohort, 28 received tracheostomy and 26 required assistance with ventilation only in sleep at age 9 months. This shows that these patients can have good survival with multidisciplinary care.

Among individuals with the mutation-based, congenital form of the disease, neurocognitive outcomes are often related to the nature and timing of ventilation (104). Nonetheless, most individuals generally demonstrate low-average intelligence (104). Moreover, awareness of other associated conditions – from clinically significant dysautonomia (most importantly lethal asystole) to gastrointestinal dysmotility to neural-crest-cell-derived tumors – has led to a multidisciplinary approach that can effectively assess and manage all dimensions of care resulting in only a modest adverse impact of the condition on patient quality of life (112).

Special considerations

Pregnancy

Patients with congenital central alveolar hypoventilation syndrome often have children of their own. The theoretical hazard of reduced central ventilatory drive in congenital central alveolar hypoventilation syndrome, combined with the mechanical load of the enlarging uterus, mandates frequent respiratory monitoring with mechanical ventilation in sleep and during spontaneous breathing while awake (03). As such, in apparently healthy individuals late-onset CHS might be unmasked by an otherwise uncomplicated pregnancy (97). In individuals with a known congenital central hypoventilation syndrome phenotype, prenatal PHOX2B gene testing of the fetus is also recommended to plan care of the newborn.

Anesthesia

Anesthesiologists should be made aware of the disorder in order to plan for appropriate postoperative airway and ventilatory management. Patients with congenital central hypoventilation syndrome are more likely to have an adverse event related to general anesthesia (16). A case series of children undergoing diaphragmatic pacemaker placement found that over three fourths of the children had peri or intraoperative events of hypoxemia, hypotension, bradycardia, bronchospasm, hypoventilation, or developed pneumonia or atelectasis (16). Another case reported successful anesthetic management and recovery from a dental procedure in a child with congenital central hypoventilation syndrome and Hirschsprung disease (47). Another case involved a child who presented with unanticipated postoperative respiratory complications after anesthesia for elective tonsillectomy; the child eventually required a tracheostomy and long-term ventilatory support (66). One report highlights the following considerations regarding administration of anesthesia to central alveolar hypoventilation patients (77):

In instances where general anesthesia is required, adjunct pharmacologic management may help with postoperative extubation. One case report suggested that caffeine may lead to a more rapid emergence from anesthesia through elevation of ionized cyclic adenosine monophosphate and blockade of the adenosine receptor (23). Comparatively, in individuals with TBI-related acquired central alveolar hypoventilation, a small case series suggested that treatment with 5HT3 receptor antagonist, ondansetron, helped improve ventilator synchrony, potentially through blockade of inhibitory neurons that terminate in the ventral respiratory group (67). On occasion, central hypoventilation due to brainstem lesions or compression may be unmasked with the use of anesthesia (113).

Parents of children with CCHS

Chronic respiratory disease in childhood can be a major stressor for families. The parents of children with congenital central hypoventilation syndrome have poor sleep quality, increased daytime sleepiness, and higher scores on a depression index than the parents of healthy subjects (82). In such cases, is important to counsel parents on the importance of their own wellness as well as establish cautious but hopeful expectations regarding the efficacy of therapies.