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Tracheomalacia in adults: Clinical features and diagnostic evaluation

Tracheomalacia in adults: Clinical features and diagnostic evaluation
Literature review current through: Jan 2024.
This topic last updated: Oct 11, 2023.

INTRODUCTION — Tracheomalacia (TM) refers to weakness in the airway wall resulting in excessive airway narrowing during expiration. The epidemiology, clinical manifestations, and diagnosis of TM in adults are reviewed here. Treatment of TM and TM in children are discussed separately. (See "Tracheomalacia in adults: Treatment and prognosis" and "Congenital anomalies of the intrathoracic airways and tracheoesophageal fistula".)

DEFINITIONS AND TERMINOLOGY — Pertinent definitions are shown in the figure (figure 1).

Expiratory central airway collapse (ECAC) encompasses two distinct pathophysiologic entities: excessive (or hyper) dynamic airway collapse of the posterior membrane (EDAC) and tracheobronchomalacia (TBM). EDAC is also known as membranous malacia and can coexist with TM, bronchomalacia (BM), and TBM (ie, cartilaginous malacia).

TM could present as diffuse or segmental weakness of the tracheal wall resulting in abnormal airway narrowing. It can be further subcategorized as cartilaginous TM (limited to the anterior or lateral wall) or circumferential TM (involves anterior and lateral walls).

BM exists when the cartilage weakness involves one or both mainstem bronchi.

TBM exists when the cartilage weakness involves the trachea and one or both mainstem bronchi.

We refer to TM, BM, TBM, and EDAC collectively as TM in this review since all these conditions have a similar clinical presentation, diagnostic evaluation, and sometimes similar therapeutic approach [1]. The terms TBM and EDAC are frequently used interchangeably in practice. We distinguish between the disorders when necessary.

Tracheomegaly is an enlarged trachea and is most often encountered in children. Further details are below. (See 'Congenital (tracheomegaly)' below.)

CLASSIFICATION — Several classification systems exist for TM:

Tracheal appearance – TM can be classified according to the appearance of the trachea:

Crescent – Patients who have anteroposterior tracheal narrowing are said to have crescent-shaped TM (ie, scabbard shape) (figure 2).

Lateral – Patients who have lateral tracheal narrowing are said to have saber-sheath TM (ie, fissure shape) (picture 1).

Circumferential – Less frequently, some patients may have both anteroposterior and lateral narrowing and are said to have circumferential TM, as seen in relapsing polychondritis (picture 2).

Distribution – TM can be classified according to its distribution, as segmental or diffuse, tracheal, bronchial, or both. This is particularly useful for guiding therapy. (See "Tracheomalacia in adults: Treatment and prognosis".)

Etiology – TM can be classified as congenital (ie, primary) or acquired (ie, secondary) (table 1) [2,3]. In adults, acquired TM is presumed to be more common than congenital TM.

EPIDEMIOLOGY — The prevalence of adult TM in the general population is uncertain because reports have been based on rates in patients with specific conditions instead of general populations. In addition, there is no clear cutoff that distinguishes normal physiologic from pathologic tracheal expiratory collapse leading to different definitions for TM throughout the literature.

Older studies indicate that acquired TM is most common in males older than 40 years of age [4-9]. The exception is relapsing polychondritis (RP) where severe airway manifestations due to RP are three times more likely in females than males [10].

In one study of 10 healthy subjects, 40 percent had a reduction of at least 50 percent of tracheal luminal cross-sectional area on dynamic expiratory computed tomography (CT), but none had a decrease of greater than 61 percent [11].

The prevalence in the general population is likely overestimated. While older studies used a >50 percent narrowing of the airway, newer diagnostic criteria have since been proposed and are more stringent (eg, >70 percent). In a study of 50 healthy volunteers, the false positive ratio decreased from 65 to 22 percent when the threshold was increased from >50 to >70 percent collapsibility [12]. Therefore, it has been suggested that the threshold for the diagnosis of TM be >70 percent tracheal collapse [11,13,14] (see 'Diagnostic criteria' below). Of note, in specific airway locations in normal individuals, airway collapse can be even more significant (>80 percent) as seen in the bronchus intermedius during dynamic CT. Thus, no decision regarding treatment should be based simply on the degree of airway collapse during forced exhalation.

Prevalence in specific populations is discussed below. (See 'Etiologies' below.)

ETIOLOGIES — Acquired TM is the most common cause of TM in adults while congenital TM is the more common cause of TM overall. Congenital TM presents in childhood but is occasionally seen in adults.

Acquired — Adult TM is associated with several comorbidities. In our experience, chronic obstructive pulmonary disease (COPD) is the most common comorbidity in which TM is seen, but other conditions, such as prior airway injury (mechanical, thermal, radiation) and external compression, may also be associated with TM (table 1) [2]. It should be noted, however, the association between TM and these entities is not necessarily causal.

Chronic inflammation or infection – Airway inflammation and recurrent infection have been implicated in TM, including the following conditions:

COPD/emphysema – A substantial proportion of patients with severe emphysema (13 to 27 percent) and up to 5 percent of smokers have TM, suggesting that chronic inflammation due to the inhalation of irritants (eg, cigarette smoke) may cause TM [6,15-18]. Recurrent infections, chronic aspiration, and chronic use of high-dose inhaled corticosteroids may also play a role [19].

It should be noted that the excessive collapse of the posterior membrane seen in COPD/emphysema is also a consequence of peripheral airway obstruction and not necessarily due to central airway wall weakness. Similarly, the high-dose inhaled corticosteroid association with TM may be because patients with severe COPD require these medications and their central airway collapse is due to their severe peripheral airway disease. Distinguishing these mechanisms from one another is not possible.

A meta-analysis of 41 studies, totaling over 10,000 individuals, reported a prevalence of 27 percent in patients with chronic obstructive airway disease (ie, asthma and COPD) compared with 17 percent of healthy subjects [15]. The high prevalence in healthy individuals suggests that the diagnostic criteria used in most studies may not accurately represent the true prevalence rate of TM.

In a study from Japan, in which 4283 patients with pulmonary disease (mostly COPD) underwent bronchoscopy [9], TM, as evidenced by airway narrowing greater than 50 percent, was found in 13 percent of patients.

Bronchiectasis – TM is common among adults who have bronchiectasis. In an observational study that included 40 adults with bronchiectasis due to cystic fibrosis (CF) and 10 healthy volunteers, TM was detected by CT in over two-thirds of the patients with CF and none of the controls [20]. (See "Cystic fibrosis: Clinical manifestations and diagnosis".)

Relapsing polychondritis (RP) – RP leads to the destruction of cartilage and is associated with TM that is commonly circumferential (image 1) [21]. In one study, nearly 50 percent of patients with RP who were evaluated for airway involvement exhibited some degree of TM. Once TM develops in these patients, prognosis is poor as the process is diffuse and involves the entire cartilaginous ring. (See "Clinical manifestations of relapsing polychondritis", section on 'Large airway involvement'.)

Trauma – Tracheal injury is associated with TM.

Tracheostomy or endotracheal intubation can damage the tracheal cartilage at the stoma or cuff site, respectively, which weakens the tracheal wall [2]. This type of TM is usually focal (ie, short-segment), with a length of 3 cm or less (picture 3). Possible risk factors are similar to those of postintubation stenosis and include recurrent intubation, prolonged intubation, concurrent high-dose steroid therapy, cuff pressures >25 cm H2O, prone positioning, and obesity. The mechanism is uncertain but is likely due to pressure necrosis, impaired blood flow, recurrent infections, mucosal friction, or mucosal inflammation, and eventually, chondritis [22]. (See "Complications of the endotracheal tube following initial placement: Prevention and management in adult intensive care unit patients", section on 'Maintain optimal cuff pressure'.)

Other types of tracheal cartilage injury can also cause TM. These include strangulation, external chest trauma, radiation, and surgery (eg, lung transplantation) [23-25].

External compression – Chronic external compression of the trachea can cause TM. This is most commonly due to a benign mediastinal goiter [5]. In a study of 51 patients who underwent surgery to remove a large goiter, significant central airway collapse was identified in 78 percent [5]. This value likely overestimated the true prevalence of TM since it used diagnostic criteria that have been subsequently amended. (See 'Diagnostic criteria' below.)

However, it can also be due to external compression from malignancy, vascular compression (eg, vascular ring, aortic aneurysm), abscess, cyst, or other benign lesions.

Gastroesophageal reflux disease (GERD) and others – Other conditions associated with TM include exposure to mustard gas [26], foreign bodies, and GERD [26,27].

Obesity – Morbid obesity may influence several aspects of airway function and anatomy. These changes are more prominent in patients with asthma and COPD. For this reason, we evaluate these patients for TM, especially when their underlying obstructive lung disease is difficult to control and they remain symptomatic despite escalating airway therapies [28,29].

Congenital (tracheomegaly) — Most types of congenital TM manifest during early childhood and are due to inherited diseases that weaken the trachea (eg, mucopolychondritis). These disorders are discussed separately. (See "Congenital anomalies of the intrathoracic airways and tracheoesophageal fistula".)

Idiopathic giant trachea (IGT) is a type of congenital tracheomegaly that typically presents during adulthood. It is a rare condition caused by atrophy of the longitudinal elastic fibers and thinning of the muscularis mucosa of the trachea [30]. The cause of tracheobronchomegaly is uncertain but may be partially familial [31]. IGT can also present as tracheobronchomegaly (Mounier-Kuhn syndrome) when the defect extends into the central bronchi [32]. The syndrome is often associated with Ehlers-Danlos syndrome, Marfan syndrome, and cutis laxa. Airway diverticula can also be seen in patients with Mounier-Kuhn syndrome. The peripheral airways maintain a normal diameter [33]. Diagnosis on CT is discussed below. (See 'Dynamic airway CT' below.)

CLINICAL MANIFESTATIONS — The clinical manifestations of TM in adults (including tracheomegaly due to Mounier-Kuhn syndrome) range from no symptoms to stridor (in extrathoracic TM), depending upon the severity and location of TM and the presence of underlying lung disease.

History and examination — The most common symptoms of TM in adults are the following [34-39]:

Dyspnea – Dyspnea can occur at rest or during exertion.

Cough – The cough has a barking quality (likened to a barking seal). Severe paroxysms of coughing may interrupt daily activities and even cause syncope. Patients may even note difficulty with expectoration.

Sputum retention – Recurrent pulmonary infections (eg, more than three per year) are common due to difficulty in expectorating secretions.

Less commonly, episodic choking may occur. Stridor only occurs when TM is confined to the extrathoracic trachea, usually seen in patients with focal TM postintubation/tracheostomy.

These manifestations are nonspecific and are often attributed to alternative diagnoses, including emphysema, chronic bronchitis, bronchiectasis, cigarette smoking, or asthma. When TM coexists with one or more of these conditions, symptoms that seem out of proportion to the severity of the underlying condition or persistent symptoms despite optimization of therapy should raise the suspicion for TM.

TM can be asymptomatic, especially if the airway narrowing is mild to moderate. In such cases, symptoms or signs may develop as the severity of airway narrowing progresses or if there is a trigger (eg, during an infection, general anesthesia, failure to liberate from mechanical ventilation) [40,41]. Alternatively, TM may be suspected incidentally on chest CT or bronchoscopy performed for another reason.

There are no specific examination findings, although wheeze or stridor may be apparent and expiration may be truncated. Early wheezing during exhalation suggests central airway collapse. A goiter may be present if that is the underlying reason for TM. Maneuvers can sometimes elicit signs of TM, including forced expiration, cough, a Valsalva maneuver, and certain positions (eg, recumbency).

In patients with relapsing polychondritis, inflammation of the ear, larynx and nasal cartilaginous structures could be manifestations of disease and concurrent with tracheal wall inflammation causing TM.

Chest radiography — Routine anteroposterior and lateral chest radiographs do not typically show an abnormality. In circumstances in which the TM is caused by compression from other structures, the underlying abnormality may be detectable on the chest radiograph (eg, mediastinal goiter) [2].

The lack of findings on chest radiography is explained by the fact that airway narrowing due to TM is a dynamic process, only occurring at certain points during the respiratory cycle (typically expiration). In addition, tracheal narrowing can be difficult to appreciate on chest radiography since the air column typically narrows in the subglottic region.

Rarely, an enlarged trachea, classic of tracheomegaly, may be appreciated on chest radiography.

Differential diagnosis — Since the symptoms of TM are nonspecific, the differential diagnosis includes chronic obstructive pulmonary disease, asthma, interstitial lung diseases, vocal cord dysfunction, expiratory flow limitation due to obesity, and gastroesophageal reflux disease. Most of these conditions can be differentiated by investigating tests, including chest CT, pulmonary function testing, and bronchoscopy, which are all generally performed for suspected TM. (See "Evaluation and treatment of subacute and chronic cough in adults" and "Approach to the patient with dyspnea" and 'Diagnostic approach' below.)

Occasionally, in those with recurrent infections, we exclude immunoglobulin deficiency by measuring immunoglobulin levels. (See "Primary humoral immunodeficiencies: An overview".)

DIAGNOSTIC APPROACH — TM may be suspected based upon a patient's symptoms and signs (see 'Clinical manifestations' above). Alternatively, TM may be suspected based upon chest CT or bronchoscopy that were performed for a different reason. In patients with suspected TM, we perform noncontrast dynamic airway CT (DACT) and dynamic flexible bronchoscopy (DFB), which complement each other diagnostically. If not already performed, we also obtain pulmonary function testing (PFT) with flow volume loop (FVL) assessment, which provides supportive data but is not diagnostic. (See 'Diagnostic tests' below and 'Supportive testing' below.)

Supportive testing

Pulmonary function tests and flow volume loop — In patients with suspected TM, we perform PFT with spirometry and FVL assessment to provide supportive data for the diagnosis of TM.

Spirometry classically demonstrates obstruction that is proportional to the severity of the TM [42,43]. However, a wide range of abnormalities have been reported, including restriction and mixed defects, which limit their use as a sole diagnostic tool. In a descriptive study of 90 patients with moderate to severe TM who underwent PFTs, 44 percent of patients had an obstructive ventilatory defect, 18 percent had a definite or highly likely restrictive ventilatory defect, 17 percent had a mixed defect, and 21 percent were within normal limits [44]. (See "Overview of pulmonary function testing in adults".)

The FVL classically shows obstruction with low peak expiratory flow rate followed by a rapid decrease of flow (figure 3). However, a restrictive, notched, oscillatory, or normal FVL may also occur.

In one study, the most frequent finding was a low maximal forced expiratory flow (FEFmax) in 82 percent of cases, followed by biphasic morphology in 20 percent, notched expiratory loop in 9 percent, expiratory oscillations (alternating decelerations and accelerations of flow "saw-tooth") in 3 percent, and 17 percent had no distinctive FVL abnormality (figure 4) [44]. While flow oscillations are associated with possible TM in up to a one-third of patients, oscillations are nonspecific [45] and have been found to occur in other conditions, including redundant pharyngeal tissue, patients with excessive secretions, neuromuscular disease, or structural or functional disorders of the larynx [45-47]. (See "Flow-volume loops".)

Diagnostic tests — In patients with suspected TM, we perform noncontrast dynamic airway CT (DACT) and dynamic flexible bronchoscopy (DFB), both of which are performed using forced exhalation maneuvers. Demonstration and practice of forced exhalation maneuvers is key to both DFB and DACT diagnosis [13].

While visualization of TM during bronchoscopy is considered the gold standard diagnostically, both DACT and DFB are performed because the two tests are complementary. As examples:

Sedation for bronchoscopy may prevent maximal effort during a forced exhalation maneuver, thereby underestimating the severity of the dynamic airway collapse. When the forced exhalation maneuver is performed during a CT scan, the collapsibility of the airway may be more accurately determined as the patient is not sedated. On the other hand, if the CT image is taken during end-exhalation rather than during the forced exhalation maneuver, it may also underestimate the degree of collapse [48].

DACT is better able to locate the distal extent of the TM when it extends into the segmental and subsegmental bronchi. This has implications for treatment since neither stenting nor surgical options can correct distal bronchial disease. DACT also provides objective measurements of anterior-posterior and lateral dimensions as well as cross-sectional area.

DFB provides information about the presence of coexisting conditions (paradoxical vocal fold motion, laryngopharyngeal reflux, and airway infection or inflammation) as well as the ease of navigation into and within the airways, which is useful for planning future interventions.

Of note, while the forced expiratory maneuver during imaging is needed to diagnose TM, the severity of airway collapse revealed during such maneuvers is not necessarily physiologically consequential. In fact, one study showed that if 50 percent collapse criterion is used to diagnose TM, almost 80 percent of normal individuals would have this diagnosis, especially when evaluating bronchus intermedius collapse [12].

Dynamic airway CT — In patients with suspected TM, we perform noncontrast DACT, which is used to calculate airway collapsibility. DACT may also reveal a potential underlying etiology (eg, goiter, vascular ring, emphysema, bronchiolitis, bronchiectasis, Mounier-Kuhn syndrome (table 1)).

Image acquisition – DACT involves image acquisition taken at the end of inspiration and continuously during a forced exhalation maneuver in a caudal-cranial direction. The airways are measured in cross-section on images obtained at end-inspiration and end-expiration. A high-quality study requires patient cooperation and coordination with experienced radiology staff.

The appearance of TM includes the following on an adequate dynamic expiratory image:

Flat or anterior bowing of the posterior tracheal wall

Smaller anteroposterior airway diameter than lateral diameter

An increase in surrounding lung attenuation

Calculating airway size – When these criteria are met, the degree of airway collapse can be accurately measured (image 2). To calculate the degree of airway collapse or collapsibility index (CI), the dynamic expiratory area (DEA) is subtracted from the area at end inspiration (AEI) and this number is then divided by the AEI and multiplied by 100. CI = (AEI-DEA/AEI) x 100 (image 3) [49]. Criteria for diagnosing TM by DACT are currently the same as those for diagnosing TM by bronchoscopy and are discussed below. (See 'Diagnostic criteria' below.)

Incidental findings – Tracheobronchomegaly can be diagnosed when the diameter of the trachea, right mainstem bronchus, and left mainstem bronchus exceed 3, 2.4, and 2.3 cm, respectively (image 4) [50]. These measurements represent three standard deviations above the upper limit of normal in adults. Normal tracheal dimensions are described separately. (See 'Congenital (tracheomegaly)' above and "Presentation and diagnostic evaluation of non-life-threatening and nonmalignant subglottic and tracheal stenosis in adults", section on 'Normal anatomy and tracheal dimensions'.)

DACT may also show bronchiectasis, bullous emphysema, pulmonary fibrosis, and tracheal diverticula [30,51,52]. Tracheal diverticula are complications of TM that may be due to the increased global compliance of the tracheal wall and the development of redundant membranous tissue [51,52].

Data describing the diagnostic sensitivity of DACT are limited. When performed adequately in cooperative patients, the diagnostic accuracy rate may be as high as 97 percent [11,43,53,54].

At least one observational study has found that DACT can reliably predict TM, especially when the predictive measure is the degree to which the sagittal (anteroposterior) diameter decreases from end-inhalation to end-exhalation [53].

Few high-quality studies have compared DACT with bronchoscopy. One pilot study that retrospectively gathered information from patients who had bronchoscopically confirmed TM reported that DACT (performed within one week of bronchoscopy) correctly identified TM in 97 percent of patients [54]. Another study reported that CT correlated well with degree of collapse seen during bronchoscopy [43]. However, data reporting that collapse >50 percent can be seen in up to 78 percent of "healthy" volunteers suggest that CT may over estimate TM or that more stringent parameters for the diagnosis are needed [12,55].

Newer CT techniques may improve the sensitivity of DACT for the diagnosis of TM. Ultrafast multidetector CT scanners permit volumetric central airway imaging in only a few seconds. This allows true dynamic assessment of TM because the airway can be imaged during a forced exhalation or cough maneuver [56]. Preliminary data have shown that using an ultra-low dose (ULD) CT scan technique (eg, low effective dose of less than 0.1 millisievert) obtained good image quality when compared with a typical-dose CT scan. Further studies are needed to validate the diagnostic accuracy of ULD techniques for patients with TM [57].

Criteria for diagnosing TM are discussed below. (See 'Diagnostic criteria' below.)

Dynamic flexible bronchoscopy — In patients with suspected TM, we perform DFB to visually confirm TM and to assess the type and extent of TM.

The procedure is as follows:

DFB is performed in spontaneously breathing patients under minimal sedation with fentanyl, midazolam, and local anesthesia (eg, 1 percent lidocaine) when the patient can follow commands. We prefer a standard flexible bronchoscope since a rigid bronchoscope may unintentionally stent the airway open and underestimate the degree of collapse. (See "Flexible bronchoscopy in adults: Overview" and "Flexible bronchoscopy in adults: Preparation, procedural technique, and complications".)

The airways should be evaluated at several levels including middle trachea, distal trachea, proximal and distal right and left main stem bronchi, and proximal bronchus intermedius, and proximal and distal left and proximal bilateral mainstem bronchi.

During bronchoscopy, airway narrowing is assessed at tidal breathing. Patients are then asked to take a deep breath in, hold it, and then forcefully expire, and the tracheal lumen is observed for narrowing. This procedure should also be repeated at the proximal right and left mainstem bronchi. We do not use deep breathing, Valsalva maneuvers, or cough to elicit airway collapse during bronchoscopy. However, the significance of airway collapse in response to such maneuvers is unknown because the degree of airway collapse and the amount of expiratory effort have never been correlated and sometimes such maneuvers can induce bronchospasm.

The maneuver is repeated three times at each point to ensure maximal airway narrowing during exhalation. The observer estimates the percentage of luminal narrowing based upon images taken at end-inspiration and end-expiration (image 2). Subjective and objective measures can be made to determine the degree of collapse present. Objective measurements are similar to that described for DACT. (See 'Dynamic airway CT' above.)

Data that support DFB as a diagnostic tool are limited. In a pilot study, there was favorable inter- and intra-observer agreement among 23 pulmonologists using DFB to estimate the degree of airway collapse [55]. Data comparing DACT and DFB are described above. (See 'Dynamic airway CT' above.)

Criteria for diagnosing TM by bronchoscopy are discussed below. (See 'Diagnostic criteria' below.)

The value of DFB with continuous positive airway pressure (CPAP) titration when CPAP is chosen as a therapy for TM is discussed separately [58]. (See "Tracheomalacia in adults: Treatment and prognosis", section on 'Intermittent noninvasive positive airway pressure'.)

Diagnostic criteria — Although DFB and DACT are performed during the diagnostic evaluation for TM, many experts consider bronchoscopic visualization of dynamic airway collapse the diagnostic gold standard for diagnosis and use DACT to accurately determine the percentage of collapsibility, although morphometric bronchoscopy can be used to objectively assess degree of narrowing by bronchoscopy [59,60]. In addition, respiratory symptoms that are not fully explained by another pathology, such as chronic obstructive pulmonary disease, asthma, vocal cord dysfunction, or inflammatory diseases, should be present. Some experts also consider the demonstration of dynamic airway collapse on DACT as diagnostic, although more research is needed to define exact parameters that accurately predict the diagnosis.

We use a more rigorous criterion than the historically chosen airway narrowing >50 percent to diagnose TM. With the caveat that the below values are not justified physiologically, we have changed our thresholds to the following:

Normal – The lumen narrows by <70 percent of its initial size during expiration

Mild TM – The lumen narrows by 70 to 80 percent

Moderate TM – The lumen narrows by 81 to 90 percent

Severe TM – The lumen narrows by >90 percent or the anterior and posterior walls touch (picture 4)

Historically, TM was diagnosed if there was >50 percent decrease in airway lumen size, but data have shown that this threshold was met in up to 78 percent of healthy volunteers [12,55]. Thus, we believe that the diagnostic criterion of >50 percent luminal narrowing may not be the optimal diagnostic threshold as it results in overdiagnosis. These findings underscore the variability of the normal collapsibility of the trachea. More research is needed to define what threshold might be used to accurately predict clinically significant collapse of the airway. This variability and uncertainty in diagnostic thresholds is the main reason why patients undergo trials of stent therapy rather than proceeding directly to tracheobronchoplasty. (See "Tracheomalacia in adults: Treatment and prognosis", section on 'Persistent symptoms'.)

POSTDIAGNOSTIC TESTING — Once the diagnosis is made, we routinely also perform the following:

Laryngoscopy – We perform laryngoscopy to evaluate for vocal cord dysfunction (VCD) since the prevalence of VCD is high in patients with TM. (See "Inducible laryngeal obstruction (paradoxical vocal fold motion)".)

Esophageal pH-impedance study – We also perform esophageal impedance to evaluate for significant gastroesophageal reflux disease (GERD) since GERD is present in 45 percent of patients with TM [27]. (See "Esophageal multichannel intraluminal impedance testing".)

Pulmonary function tests (PFTs) – We perform PFTs, if not already performed, to evaluate for underlying lung disease. (See "Chronic obstructive pulmonary disease: Diagnosis and staging" and "Asthma in adolescents and adults: Evaluation and diagnosis" and "Approach to the adult with recurrent infections" and "Approach to the adult with recurrent infections", section on 'Initial immunologic evaluation'.)

We use the existing chest CT to evaluate for other potential etiologies, such as masses causing external tracheal compression, vascular abnormalities, goiter, and bronchiectasis.

HISTOPATHOLOGY — Since biopsy is not required or feasible for the diagnosis, little is known about the histopathologic changes associated with TM in adults. Autopsy studies have found anteroposterior narrowing of the lumen accompanied by atrophy of the longitudinal elastic fibers and fragmentation of the tracheal cartilage [6,7,9,61-63].

One study compared surgical resection specimens from patients with TM and tracheal stenosis (TS) with control tracheal specimens obtained from autopsy cases [64]. Airways of both patients with TM and TS had submucosal fibrotic changes, with TM specimens having alterations in elastin fiber quality and density in the posterior membrane. In patients with TM, there was a higher expression of fibroblast growth factor binding protein-2 and fibroblast growth factor receptor-3 compared with patients who had TS and control patients; expression of tumor growth factor-beta and tissue inhibitor of metalloproteinases-1 were also elevated when compared with control patients.

SUMMARY AND RECOMMENDATIONS

Terminology – Expiratory central airway collapse (ECAC) encompasses two distinct pathophysiologic entities: excessive dynamic airway collapse of the posterior membrane (EDAC) and tracheobronchomalacia (TBM). EDAC is also known as membranous malacia and can coexist with tracheomalacia (TM), bronchomalacia (BM), and TBM (ie, cartilaginous malacia) (figure 1).

TM refers to diffuse or segmental tracheal wall weakness.

BM denotes diffuse or segmental bronchial wall weakness.

TBM exists when the airway wall weakness extends into one or both mainstem bronchi.

All conditions, collectively referred to as TM in this topic, result in exaggerated luminal narrowing during expiration and have similar clinical presentation, diagnostic evaluation, and treatment (figure 2). (See 'Definitions and terminology' above.)

Epidemiology and etiology – The prevalence of TM is uncertain. In adults, acquired TM is more common than congenital TM and is commonly associated with underlying disorders, including chronic lung disease (table 1).

Clinical manifestations – Common manifestations of TM in adults are dyspnea, cough, sputum retention, and recurrent respiratory infections and even respiratory failure. Others include wheeze and stridor. However, TM can be asymptomatic, especially if the airway narrowing is mild or moderate, or found incidentally on chest CT or bronchoscopy. Manifestations of TM are nonspecific and often attributed to alternative diagnoses leading to diagnostic delay. (See 'Clinical manifestations' above.)

Diagnostic approach – In patients with suspected TM, we perform noncontrast dynamic airway CT (DACT) (image 1 and image 2 and image 3) and dynamic flexible bronchoscopy (DFB) (picture 4 and picture 1 and picture 2). We also obtain pulmonary function testing (PFT) with flow volume loop assessment, which provides supportive data but is not diagnostic (figure 3).

To calculate the degree of airway collapse or collapsibility index (CI), the dynamic expiratory area (DEA) is subtracted from the area at end inspiration (AEI) and this number is then divided by the AEI and multiplied by 100. CI = (AEI-DEA/AEI) x 100 (image 3) [49]. (See 'Diagnostic approach' above.)

Diagnostic criteria – Criteria for the diagnosis of TM are the same, regardless of which test is used to measure luminal narrowing (DFB, DACT). (See 'Diagnostic criteria' above.)

A proposed criterion for TM is >70 percent decrease in airway lumen area when end-inspiratory and end-expiratory measurements during a forced exhalation maneuver are compared.

We classify TM severity as:

-Normal – The lumen narrows by <70 percent of its initial size during expiration

-Mild TM – The lumen narrows by 70 to 80 percent

-Moderate TM – The lumen narrows by 81 to 90 percent

-Severe TM – The lumen narrows by >90 percent or the anterior and posterior walls touch (picture 4)

Follow up tests – Once the diagnosis is made, we routinely also perform PFTs (if not already performed), laryngoscopy, and esophageal pH-impedance testing to assess for the presence of coexisting obstructive lung disease, vocal cord dysfunction, and gastroesophageal reflux disease, respectively. We use the existing chest CT to evaluate for other potential etiologies, such as masses causing external tracheal compression, vascular abnormalities, goiter, and bronchiectasis. (See 'Postdiagnostic testing' above.)

ACKNOWLEDGMENT — The UpToDate editorial staff acknowledges Armin Ernst, MD, FCCP, Kelly Carden, MD, and Sidhu Gangadharan, MD, who contributed to earlier versions of this topic review.

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Topic 4406 Version 31.0

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