Mounier–Kuhn Syndrome - All About the Respiratory Tract Infection

What Is Mounier-Kuhn Syndrome?

Mounier-Kuhn syndrome is an uncommon clinical and radiologic disease. The condition is generally congenital, meaning the child is born with the condition. Various doctors and authors use Mounier-Kuhn syndrome synonymously with the term tracheobronchomegaly. Tracheobronchomegaly is an extremely uncommon congenital lung condition principally distinguished by an abnormal enlargement and widening of the upper airways. Mounier-Kuhn syndrome is distinguished by significant tracheal and bronchial dilatation and recurring lower respiratory tract infections.

Prof. Pierre-Louis Mounier-Kuhn first described the condition in 1932, giving way to the phrase "Mounier-Kuhn syndrome," whereas Katz et al. first used the word "tracheobronchomegaly" in 1962. And the total number of cases described in the medical literature is less than 100. Congenital atrophy of the elastic and smooth muscle of the trachea and major bronchi has been seen in biopsy tests, but the exact cause of the disorder is unknown. Tracheobronchomegaly associated with Mounier-Kuhn syndrome may also be accompanied by tracheal and bronchial diverticula (pouches arising from the bronchial tube).

Who Is Affected by Mounier-Kuhn Syndrome?

• Mounier-Kuhn syndrome is more common in men than women, and the condition is reported in men below 50.

• The condition is generally diagnosed between the third and fourth decades of life.

What Are the Subtypes of Mounier-Kuhn Syndrome?

Mounier-Kuhn syndrome has the following three subtypes:

• Type 1: The trachea and major bronchi exhibit a mild symmetric dilation in type 1.

• Type 2: This type presents with discrete diverticula and dilatation of the trachea and major bronchi.

• Type 3: Diverticular and saccular features reach the distal bronchi in type 3.

What Causes Mounier-Kuhn Syndrome?

• Mounier-Kuhn syndrome occurs due to elastic fibers atrophy (in the trachea and main bronchi), which results in thinning of the smooth muscle layer and eventually causes abnormal tracheobronchial flaccidity, widening, and collapse. However, the exact mechanism of its etiology is still unknown.

• Certain factors like cigarette smoking and air pollutants can act as precipitating factors.

• The condition is occasionally linked to connective tissue disorders such as cutis laxa, Marfan syndrome, and Ehlers-Danlos syndrome and may have a genetic basis; however, no genetic variation has been discovered to date.

What Are the Symptoms of Mounier-Kuhn Syndrome?

The sign and symptoms of Mounier-Kuhn syndrome include the following:

• In the absence of infection, Mounier-Kuhn syndrome can progress asymptomatically, and in many instances, the symptoms are non-specific.

• In mild occurrences, individuals have normal lung function, either show no symptoms or only present with chronic cough.

• Recurrent lower respiratory tract infections.

• Different degrees of tracheobronchial irritation results in a persistent dry cough or productive cough and the production of purulent sputum.

• Dyspnea or shortness of breath.

• Hemoptysis (blood mixed with cough).

• Hoarseness of voice.

• Bronchial crackles.

• Wheezing.

• Clubbing of fingers.

• Clinical traits of Mounier-Kuhn syndrome can resemble COPD (chronic obstructive pulmonary disease) symptoms.

• In extremely rare severe cases, patients may have airflow restriction and obstructive pulmonary illnesses such as bronchiectasis or bullous emphysema. These conditions can cause chronic respiratory failure.

What Is the Differential Diagnosis of Mounier-Kuhn Syndrome?

Several connective tissue diseases that affect the lungs can be considered as the differential diagnosis of Mounier-Kuhn syndrome:

• Ataxia-Telangiectasis: It is an uncommon disease affecting children. Uncoordinated movements characterize it, and the condition affects the brain and other body parts. Telangiectasis refers to enlarged capillaries present below the skin surface.

• Ankylosing Spondylitis: It is an inflammatory condition that can eventually cause some of the spine's bones to fuse. Ankylosing spondylitis can also affect ribs and other bones.

• Ehler-Danlos Syndrome: A collection of genetic diseases known as Ehlers-Danlos syndrome predominantly affect the connective tissues in the skin, joints, and walls of blood vessels.

• Marfan Syndrome: Marfan syndrome is a genetic disorder. Connective tissue, or the fibers that support the body's organs and other components, is damaged by Marfan syndrome. Most frequently, the heart, eyes, blood arteries, and skeleton are affected by Marfan syndrome.

• Kenny-Caffey Syndrome: It is a very uncommon genetic skeletal illness characterized by abnormalities affecting the head and eyes, thickening of the long bones, and small marrow spaces in the bones.

• Brachmann-de Lange Syndrome: A genetic condition characterized by severe developmental abnormalities.

• Cutis Laxa: The word "cutis laxa" is a Latin phrase for "loose skin," and this condition is distinguished by saggy, non-stretchable skin. The face and other areas of the body look saggy or wrinkled because the skin frequently hangs in loose folds.

How Is Mounier-Kuhn Syndrome Diagnosed?

Mounier-Kuhn syndrome can be diagnosed in the following ways:

• CT (computed tomography): Diagnosis is generally made with the help of CT (computed tomography) scans. With the help of these scans, abnormally widened air passages are detected. When the trachea's coronal and sagittal widths are more than 25 and 27 millimeters in men and greater than 21 and 23 millimeters in women, on conventional chest radiography or CT scans, Mounier-Kühn syndrome is suspected.

• Biphasic-CT: The imaging test with the highest sensitivity is a biphasic CT with pictures of the trachea taken during inspiration and expiration. Although they are less sensitive, two-phase chest radiographs will also show the trachea expanding during inspiration and collapsing during expiration.

• Pulmonary Function Test: During pulmonary function tests, dead spaces, elevated tidal volume, and reduced bronchial flow speed may be seen. However, in mild cases, pulmonary function tests can show normal pulmonary functioning.

• Fiberoptic Bronchoscopy: Expiratory collapse in tracheomalacia patients, enlargement of the airway and proximal bronchi, and the potential development of diverticula on the posterior wall are all visible during fiberoptic bronchoscopy.

• Biopsy: Although usually unnecessary, bronchial and tracheal wall tissue biopsies reveal a decrease in elastic fibers.

How Is Mounier-Kuhn Syndrome Treated?

There is no specific cure for Mounier-Kuhn syndrome, and the treatment is usually symptomatic. Asymptomatic patients generally do not require any treatment. Management of this syndrome is done in the following ways:

• Antibiotics: Antibiotics are administered to treat lung infections and prevent further complications.

• Chest Physiotherapy: To enhance mucociliary clearance, chest physiotherapy may be suggested.

• Positive-Pressure Ventilation: Non-invasive positive-pressure ventilation, which is required at night in severe cases, may benefit certain patients.

• Quit Smoking: Reducing exposure to irritants and toxins from the workplace is quite advantageous, as is quitting smoking.

• Tracheal Stent: In some cases of tracheomalacia, inserting a tracheal or tracheobronchial stent—with or without surgical intervention—has proven to lessen airway collapsibility.

• Lung Transplant: In one instance, a double lung transplant was successful.

Conclusion:

Mounier-Kuhn syndrome is a rare yet serious condition affecting the lungs that cause the widening of the airways. The excessively widened trachea and bronchi are linked to recurrent lower respiratory tract infections, followed by profuse production of purulent sputum and other respiratory problems such as bronchiectasis. It has not been determined how this disorder affects life expectancy; therefore, the prognosis of Mounier-Kuh syndrome is unknown. Complications associated with Mounier-Kuhn syndrome, like recurrent respiratory tract infections, obstructive diseases of the lungs, pneumothorax, lung fibrosis, etc., can lead to chronic respiratory failure and death.