INTRODUCTION — Patients with neuromuscular or chest wall disease commonly have respiratory problems resulting from some combination of respiratory muscle dysfunction and decreased lung and chest wall compliance. These factors may contribute to difficulty with clearance of airway secretions, ventilation-perfusion mismatching, and eventually global alveolar hypoventilation [1]. (See "Continuous noninvasive ventilatory support for patients with respiratory muscle dysfunction".)
Sleep-disordered breathing is a significant cause of morbidity and mortality among patients with neuromuscular and chest wall disorders [2-5]. It is most often due to obstructive sleep apnea (OSA, a disorder characterized by obstructive apneas and hypopneas) or nocturnal hypoventilation, but central sleep apnea (CSA) can also be seen in patients with myotonic and muscular dystrophy [6-8]. (See "Central sleep apnea: Pathogenesis".)
INDICATIONS FOR EVALUATION OF SLEEP-DISORDERED BREATHING — Table 1 (table 1) lists symptoms that are the major factors favoring evaluation of the patient for obstructive sleep apnea (OSA), central sleep apnea (CSA), or hypoventilation, as well as some suggested physiologic criteria. However, some patients may have sleep-disordered breathing without symptoms but with suggestive physiologic parameters (eg, severe restriction on pulmonary function tests or unexplained cor pulmonale). Such patients should be evaluated with an arterial blood gas and a sleep study.
Classic symptoms of sleep-disordered breathing include excessive daytime sleepiness, morning headache, and restless sleep, but insomnia may also be seen. In addition:
●Some patients with OSA may awaken with choking or shortness of breath
●Bed partners of patients with sleep apnea often describe snoring and apnea
●Nightmares and enuresis may be symptoms of sleep-disordered breathing
Even when pulmonary dysfunction is severe, dyspnea is often lacking in patients with neuromuscular disease, probably because exercise capacity is limited by involvement of nonrespiratory muscles, thereby reducing demand on respiratory muscles.
Specific diseases — The history of a particular disease may also be helpful in some cases.
●Patients with polio who had initial involvement of respiratory, trunk, or bulbar muscles, particularly with associated scoliosis or vocal cord paralysis, are more likely than other polio patients to develop abnormalities of gas exchange during sleep [9,10].
●Kyphoscoliosis, even in the absence of neuromuscular disease, is associated with nocturnal hypoventilation and obstructive sleep apnea [11,12]. Although daytime respiratory symptoms are more common when the angle of the thoracic spinal deformity approaches 100 degrees, nocturnal oxygen desaturation is not directly correlated with the degree of scoliosis or with either lung volumes or ventilatory responsiveness. (See "Chest wall diseases and restrictive physiology", section on 'Kyphosis and scoliosis'.)
●Patients with diaphragm weakness may report increased shortness of breath in the supine position or may increase pillows or props to sleep in a more upright position [13].
●Patients with amyotrophic lateral sclerosis (ALS) are at increased risk for sleep-related breathing disorders, particularly OSA and nocturnal hypoventilation [14]. Nocturnal oxygen desaturation correlates with nocturnal hypoventilation but is insensitive and will miss approximately 30 percent of cases detected by transcutaneous capnography.
●Patients with Duchene muscular dystrophy may also have asymptomatic hypoventilation. The development of respiratory dysfunction may parallel the loss of ambulation in children or adolescents. However, following the change in forced vital capacity (FVC) over time may help determine when to do a polysomnogram and when to initiate noninvasive positive pressure ventilation. In addition, monitoring for sleep-disordered breathing may be helpful in patients who are not able to perform pulmonary function tests [15].
It is desirable to detect nocturnal gas exchange abnormalities before secondary complications result [16-18]. The clinician must therefore be alert to the presence of more subtle symptoms and signs to serve as a guide for the initiation of a sleep evaluation. Routine follow-up visits for patients with neuromuscular disease should incorporate questions about the above signs and symptoms.
Physiologic clues to sleep-disordered breathing — Certain physiologic abnormalities may also suggest the presence of sleep-disordered breathing. Patients with daytime hypoxemia and hypercarbia often have further deterioration of gas exchange in sleep. Therefore, patients with even mild abnormalities in daytime blood gases are at risk for significant disruption of nocturnal gas exchange. The most severe nocturnal oxygen desaturation is seen and should be suspected in those patients with cor pulmonale, polycythemia, and daytime systemic hypertension.
Patients with a maximal inspiratory pressure (MIP) below 60 percent of predicted, or an FVC below 1 to 1.5 L or <50 percent predicted due to amyotrophic lateral sclerosis (ALS) or other neuromuscular diseases, are more likely to have significant nocturnal desaturation [19-23]. The maximal sniff nasal inspiratory force avoids the need for a mouthpiece and thus may be better suited than the FVC and MIP for testing patients with bulbar weakness. (See "Symptom-based management of amyotrophic lateral sclerosis", section on 'Respiratory function management'.)
EVALUATION FOR CONTRIBUTING FACTORS — Patients with concomitant airflow obstruction tend to have greater gas exchange abnormalities or cor pulmonale associated with their sleep-disordered breathing than do patients with normal airway resistance. As a result, pulmonary function tests should be performed routinely for detection of coexistent airflow obstruction. Other treatable conditions that may contribute to sleep-disordered breathing in patients with restrictive thoracic disease include hypothyroidism and hypophosphatemia.
Obesity increases the risk of certain forms of sleep-disordered breathing, including obstructive sleep apnea and obesity hypoventilation syndrome.
Impaired left ventricular function occurs in some patients with obstructive sleep apnea [24]. In addition, some neuromuscular disorders, such as Duchenne and myotonic muscular dystrophies, may be associated with cardiomyopathy and conduction abnormalities [25,26]. Heart failure, particularly if associated with Cheyne-Stokes respiration, contributes to nocturnal oxygen desaturation and sleep fragmentation [24,27]. It is therefore important to assess patients with neuromuscular and chest wall disorders for possible concomitant heart failure and, if present, to institute appropriate therapy. (See "Obstructive sleep apnea and cardiovascular disease in adults".)
DIAGNOSTIC APPROACH — The essential part of the assessment is to document abnormalities of oxygenation and sleep. Overnight oximetry, portable multichannel devices suitable for home studies, and full polysomnography in the sleep laboratory are all available, but the optimal test for screening patients with neuromuscular and chest wall disorders has not been established.
The initial evaluation of patients suspected of having sleep-disordered breathing should be performed by clinicians with experience in pulmonary and sleep medicine. However, if initial screening studies are equivocal or negative and if suspicion for sleep-disordered breathing is high, the patients should be referred to a center experienced in the management of these patients, with an accredited sleep laboratory.
Polysomnography — Polysomnography (PSG) is currently considered the "gold standard" for assessing sleep-disordered breathing. False negative studies have been reported in patients with obstructive sleep apnea (OSA), although it is not clear that this problem applies to patients with non-apneic sleep-disordered breathing [28]. PSG typically includes six electroencephalogram leads, two electrooculogram leads, a submental electromyogram (EMG) lead, a nasal/oral thermistor to assess air flow, a nasal pressure transducer, thoracic and abdominal monitors to detect excursion of the rib cage and abdomen, an intercostal EMG, a snoring microphone, electrocardiogram and leg leads on the anterior tibialis, and pulse oximetry. Monitoring of multiple channels with PSG allows full assessment of possible respiratory as well as nonrespiratory sleep disorders that can coexist in patients with neuromuscular disorders. PSG can also be helpful in detecting patient ventilator asynchrony when patients have been started on noninvasive positive pressure ventilation [29,30]. Some patients with advanced neuromuscular disease may not be good candidates for an in-lab polysomnogram because of difficulty accommodating their personal needs. (See "Overview of polysomnography in adults".)
Oximetry — Overnight oximetry alone may be used to screen for oxygen desaturation associated with severe nocturnal hypoventilation in patients with neuromuscular and chest wall disease. Oximetry may underestimate the degree of sleep apnea, however, and is not considered adequate to rule out sleep apnea [28,31-33]. In addition, oximetry may have low sensitivity in detecting OSA in patients receiving supplemental oxygen.
Oximetry is helpful in screening for residual oxygen desaturation in patients who have been started on nocturnal noninvasive ventilation without evaluation in a sleep laboratory. The apnea-hypopnea index (AHI) and leak downloaded from the positive airway pressure device is helpful in assessing control of OSA, but it does not provide information about oxygen saturation, which can still be low in patients with hypoventilation. (See "Noninvasive ventilation in adults with chronic respiratory failure from neuromuscular and chest wall diseases: Practical aspects of initiation", section on 'Follow-up (adaptation phase)'.)
Home sleep apnea testing — Home sleep apnea testing (HSAT) with four or more channels (eg, heart rate, air flow, chest movement, and oximetry) is likely to detect moderate to severe OSA. However, the severity of sleep apnea may be underestimated, and mild disease may be missed entirely. In addition, sleep disruption or fragmentation, a significant factor in causing daytime sleepiness, is not assessed by oximetry or portable studies. (See "Home sleep apnea testing for obstructive sleep apnea in adults" and "Quantifying sleepiness".)
In summary, although nocturnal oximetry and multi-channel home studies are adequate to document moderate or severe disease, they should not be used to exclude a diagnosis of sleep-disordered breathing in patients with neuromuscular or chest wall disease. If there is a strong clinical suspicion of sleep-disordered breathing or otherwise unexplained excessive daytime sleepiness, but oximetry or HSAT is negative, full PSG should still be obtained [34,35].
SUPPLEMENTAL TESTS — Other tests that are more relevant for research purposes include assessment of respiratory control and intrathoracic pressure changes.
●Transcutaneous CO2 monitoring using newest generation equipment appears to be reasonably accurate [14,36,37] and, when combined with oximetry, more sensitive than nocturnal oximetry alone in detecting nocturnal hypoventilation [38]. This is particularly relevant in patients with neuromuscular disease, who may be started on noninvasive ventilation as outpatients and are in situations where arterial blood gases are not easy to obtain. (See "Polysomnography in the evaluation of sleep-disordered breathing in adults", section on 'Ventilation'.)
●End-tidal PCO2 (PETCO2) monitoring is also included in some polysomnograms, and is believed to be particularly useful in pediatric studies [39-41] (see "Evaluation of suspected obstructive sleep apnea in children"). However, one study found that PETCO2 measured from exhaled gas in a mask, particularly during use of supplemental oxygen or positive airway pressure delivery systems that incorporate a flow-through to wash out dead space, did not adequately reflect arterial values in adults [42].
●Respiratory control can be evaluated by testing ventilatory responses to hypercarbia and hypoxia, but this is rarely performed in the clinical setting. (See "Control of ventilation".)
●Esophageal pressure monitoring during sleep is helpful in distinguishing central versus obstructive apneas because it offers a sensitive way of detecting intrathoracic pressure swings related to respiratory effort. Such monitoring is also particularly useful in detecting the upper airway resistance syndrome, characterized by subtle increases in respiratory effort that are not manifested by changes in air flow but are associated with arousal and sleep fragmentation [43]. Therefore, although esophageal balloons for pressure monitoring are not yet considered standard instrumentation during polysomnography, their clinical role is gradually increasing.
SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Sleep-related breathing disorders in adults".)
SUMMARY
●Introduction – Sleep-disordered breathing is common in patients with neuromuscular or chest wall disease and is a significant cause of morbidity and mortality. The detection and therapy of sleep-disordered breathing have the potential to improve the quality and perhaps the duration of life in these patients. (See 'Introduction' above.)
●Indications for evaluation – Indications for screening include symptoms of obstructive sleep apnea (OSA), abnormalities of gas exchange, or impairment of forced vital capacity or maximal inspiratory pressure (PImax). (See 'Indications for evaluation of sleep-disordered breathing' above.)
●Evaluation – The assessment of patients with suspected sleep-disordered breathing should include:
•Physiologic measurements, such as pulmonary function tests and arterial blood gases, if not done initially.
•Metabolic studies, such as measurements of serum thyroid stimulating hormone, serum electrolytes including HCO3, and phosphate.
•An evaluation for concomitant heart failure. (See 'Evaluation for contributing factors' above.)
●Diagnostic approach – Most importantly, an assessment of breathing during sleep, which may include oximetry, home sleep apnea testing, or full in-laboratory polysomnography (PSG). Although it is not perfect, PSG is currently considered the most accurate tool for evaluating OSA and other abnormalities of sleep [28]. It is particularly useful in the evaluation of patients with neuromuscular and chest wall disorders, who may have a complex combination of nocturnal hypoventilation, central sleep apnea, and obstructive sleep apnea (table 1). (See 'Diagnostic approach' above.)
