Tracheobronchopathia Osteochondroplastica - Pathogenesis, Symptoms, Diagnosis, and Treatment

Introduction

Tracheobronchopathia osteochondroplastica (TPO) is an unlikely disorder of the large airways. It is a non-cancerous growth characterized by multiple bony or cartilaginous nodules in the tracheobronchial tree. They are found in the submucosal layer and are seen as small projections into the airway lumen. Since the growth develops from the airway cartilage, they are not seen on the posterior membraneous portion of the trachea. The condition is commonly seen in men in their 50s and does not have any link to habits like smoking or any other underlying systemic disease. The patient presents with asthma symptoms like chronic cough and wheezing and is often misdiagnosed as having asthma. Other respiratory symptoms include shortness of breath and the appearance of blood in the sputum. A common complication associated with the condition is the prevalence of recurrent pulmonary infections. The clinical symptoms are due to the narrowing and thickening of the airways because of the nodules. Though advanced imaging techniques can observe the nodules, bronchoscopy (a tube inserted into the airway for examination) alone is enough to identify the bony nodules and confirm the diagnosis. Biopsy of the nodules is rarely performed as they are benign lesions. There is no specific treatment for the condition. However, bronchodilators are used for treating breathlessness due to constricted airways, and prompt medical interventions are indicated in case of infections.

Who Is Commonly Affected by the Disorder?

Men have more prevalence for tracheobronchopathia osteochondroplastica, typically affecting people in their fifth and sixth decade of life. It is a rare disorder; on routine bronchoscopy, the estimated prevalence is only 0.7 %. Most of the reported cases are of people in their 50s.

What Are the Clinical Manifestations Of Tracheobronchopathia Osteochondroplastica?

Most of the patients reported with the condition are asymptomatic. However, the commonly presented symptoms are:

• Chronic cough.

• Dyspnea (shortness of breath) on exertion.

• Wheezing (a whistling sound heard during breathing).

• Recurrent respiratory infection.

• Chest pain.

• Systemic symptoms of fever and chills.

• Hemoptysis (blood in sputum) is occasionally seen from ulceration of the bony nodules, bronchiectasis (widening of the airways and buildup of excess mucus), or in the presence of an acute infection.

• Stridor (a grating sound on breathing) and rhonchi (bubbling sound on breathing in and out) in severe airway obstruction.

What Is the Pathogenesis of Tracheobronchopathia Osteochondroplastica?

The nodules formed in the submucosal layer of the tracheobronchial tree are either bony or cartilaginous, with a radius of one to eight millimeters. They may be focal (confined to a single area) or diffuse (distributed in different areas of the airways). Two theories of pathogenesis have been put forward.

• Ecchondrosis and exostosis of the cartilaginous rings of the tracheobronchial tree. Seen as a cartilaginous or bony outgrowth from the cartilage surface of the tracheal ring. The cause or triggering factor of the benign overgrowth is unknown.

• Osseous and cartilaginous metaplasia of internal elastic fibrous membrane. The abnormalities and metaplasia of the elastic tissues of the internal elastic fibrous membrane of the tracheobronchial tree results in bony and cartilaginous overgrowth.

The mucosa covering the nodule may be extremely thinned or edematous with an abnormal epithelium, indicating chronic inflammatory changes.

What Is the Common Location of the Nodules?

They are classically seen in the lower two-thirds of the large airways, the trachea, and the initial portions of the bronchi. The nodules are formed on the cartilaginous surface of the ring, thus affecting only the anterior and lateral walls of the tracheal ring and sparing the posterior wall, which lacks the cartilage and is membranous. In some cases, sub-glottic and laryngeal involvement has been demonstrated.

How Is the Diagnosis of Tracheobronchopathia Osteochondroplastica Made?

1. Chest Radiographs: Chest radiographs are useless in confirming the diagnosis of tracheobronchopathia osteochondroplastica. The plain two-dimensional view of the trachea will not provide evidence of the bony or cartilaginous nodules.

2. Computed Tomography: In computed tomographic imaging, the three-dimensional view of the tracheobronchial tree will reveal the bony nodules projecting into the lumen of the airways. Multiple fixed nodules that may or may not be calcified are seen in the anterior and lateral walls of the trachea. Nodules are not present on the posterior wall of the trachea. Due to the presence of the nodules, the cartilaginous tracheal rings will be deformed in the absence of external compression. However, the findings are rare in all the reported cases. Studies suggest that only four out of fifteen cases show characteristic CT findings, and the variation in the size and extent of calcification of the nodules pose a difficulty in identifying the lesion.

3. Pulmonary Function Tests: The anatomic location of the nodules in the airway and the degree of obstruction caused to the airflow will alter the results of pulmonary function tests. In mild cases, normal spirometry (a test used to measure the working of the lungs) is observed. However, in case of prominent tracheal involvement, flow volume loops (a graphical representation of the inspiratory and expiratory flow against the air volume) are used to suspect the disease and further follow-ups.

4. Bronchoscopy: Bronchoscopy is the gold standard for diagnosing tracheobronchopathia osteochondroplastica. Bronchoscopic examination reveals the nodules present in the lumen of large airways. Nodules of varying sizes (1 to 10 mm) protrude into the lumen. Laryngoscopy is used to diagnose the larynx and upper airways. A bronchoscopy will determine the lesion's extent and confirm the diagnosis.

What Are the Treatment Options and Prognosis of Tracheobronchopathia Osteochondroplastica?

There is no peculiar treatment strategy for tracheobronchopathia osteochondroplastica. Intubations in affected patients are demanding because of the calcification of tracheal rings. In case of severe obstruction of breathing, a tracheostomy is performed. Cases that have failed in conservative approaches should be treated with surgical interventions. Sectioning of the affected portion of the trachea, parietal laryngectomy (removal of a portion of the larynx), removal of the nodules using bronchoscopy, and bronchoscopic dilation are the surgical methods employed.

A favorable prognosis depends on the extent and location of the nodules. However, studies suggest more than half of the reported cases did not show any disease progression even after several years.

Conclusion

The review shows that the condition lacks distinctive clinical manifestations. It consists of benign lesions in the tracheobronchial tree that can be diagnosed through bronchoscopy, computed tomography imaging, and biopsy. The physician should be aware of the condition for a better diagnosis and management. Endoscopy can be used to treat obstructed airways.