Mac Lung Disease - Causes, Types, Symptoms, and Treatment

Introduction

Mac lung disease is an atypical respiratory infection caused by the Mycobacterium avium complex. It is a nontuberculous Mycobacterial infection that causes respiratory illness in immunocompromised individuals. It is also called Mycobacterium avium-intracellulare infection. This infection affects birds, pigs, and human beings. It is not a contagious infection.

What Is MAC Lung Disease?

Mac lung disease is a Mycobacterial infection caused by the Mycobacterium avium complex. Mycobacterium avium complex, also known as Mycobacterium avium-intracellulare complex, comprises two Mycobacterium species, namely Mycobacterium avium and Mycobacterium intracellulare. This bacteria belongs to the nontuberculous type, which is not contagious. It causes respiratory infection and affects breathing. It affects individuals with pre-existing diseases or those who are immunocompromised.

What Are the Causes of MAC Infection?

M. avium, M. intracellulare, and M. chimaera species are commonly present in soil and water. They enter the host via the gastrointestinal or respiratory tract and cause infection. It causes respiratory infection when inhaled. M. avium species also grow in bathroom shower heads. It gets aerosolized and causes infection when inhaled. Mycobacterium avium subspecies paratuberculosis (MAP) also causes infection.

How Does MAC Lung Disease Occur?

MAC is the most common nontuberculous infection. MAC enters the respiratory tract and affects the lungs and bronchi. It affects the lungs and bronchi of individuals with pre-existing conditions. The bacteria colonize the lungs and grow for many years. It causes low-grade inflammation and progressive, irreversible changes in the lungs. The lung's right middle lobe and lingula depend on vigorous cough to remove bacteria and secretions. Bronchi serve this area of the lungs. Individuals without vigorous cough develop MAC infection of the right middle lobe or left lingula of the lungs. It also causes gastrointestinal infections. The infection occurs either by inhalation or ingestion.

What Are the Types of This Infection?

The types of MAC infections are:

• Pulmonary Infection - It affects the lungs and the respiratory system.

• Disseminated Infections - This infection is common in immunocompromised individuals and those with advanced AIDS (acquired immunodeficiency syndrome). This spreads throughout the body through the bloodstream.

• MAC-Associated Lymphadenitis - It causes swelling of the lymph nodes in the neck. It usually affects healthy children.

What Are the Types of Lung Diseases Caused by MAC?

Mac causes the following lung diseases:

• Nodular Bronchiectasis - Mac infection affects the small airways and air sacs. It appears as lung nodules on radiographic images. The nodules grow slowly to cause inflammation that results in bronchiectasis. Bronchiectasis is an irreversible dilation of the airways that makes it difficult to clear the secretions and increases the risk of infections. It results in bronchitis and pneumonia if it remains untreated. It usually affects older nonsmoking women.

• Fibrocavitary Disease - MAC infection causes a hole in the lung tissues, a serious disease requiring immediate treatment. This disease usually occurs in people with emphysema or in people who smoke.

What Are the Signs and Symptoms of MAC Lung Disease?

It causes the following symptoms:

• Fever.

• Night sweats.

• Shortness of breath.

• Chest pain.

• Chronic cough with or without sputum.

• Fatigue.

• Weight loss.

• Coughing up blood.

• Anxiety.

• Lymph node enlargement.

The lymph node enlargement progresses to form an abscess that is blue-purple. This is called a collar-stud abscess. It has multiple discharging sinuses. It causes symptoms like fever, diarrhea, malabsorption, loss of appetite, and weight loss during gastrointestinal involvement. This infection can also spread to the bone marrow.

What Are the Risk Factors of This Disease?

MAC disease affects people of all ages. It has been common in women over 65 years. It affects immunocompromised individuals, people who smoke, or those with the following lung conditions:

• Bronchiectasis.

• Chronic obstructive pulmonary disease (COPD).

• Cystic fibrosis.

• Emphysema.

• Previous tuberculous infection.

What Are the Complications of MAC Lung Disease?

• MAC lymphadenitis progresses to form an abscess with multiple draining sinus tracts.

• Cavitary lesions develop secondary bacterial or fungal infections.

• AIDS-affected individuals develop immune reconstitution inflammatory syndrome (IRIS) after antiretroviral and anti-MAC therapies. This also causes enlargement of the infected lymph nodes.

How Is Mac Lung Disease Diagnosed?

The following tests are done to diagnose MAC disease.

• Chest X-Rays or CT (Computed Tomography) Scan - It is used to detect right middle lobe or left lingular lobe lung infection.

• Blood or Sputum Culture - To detect the presence of MAC infection.

• Bronchoscopy - This test is performed if sputum cultures cannot diagnose the infection.

• Bone Marrow Culture - This test is not performed during the initial diagnosis. Individuals with bone marrow involvement will have anemia and neutropenia.

How Is Mac Lung Disease Treated?

• Individuals with minimal symptoms and radiographic changes do not initially require antibiotic treatment.

• MAC infections require treatment with a three-drug regimen, including Clarithromycin or Azithromycin, Rifampicin, and Ethambutol. The treatment usually lasts for 12 months.

• A combination of anti-tuberculosis antibiotics like Rifampicin, Rifabutin, Ciprofloxacin, Amikacin, Ethambutol, Streptomycin, Clarithromycin, or Azithromycin is given for post-infection treatment.

• The drug therapy is continued for a lifetime if the clinical and microbiological improvement is observed.

• Clinical manifestations are monitored during the initial weeks of therapy. Blood cultures are done every four weeks during initial therapy to assess the microbiological response to therapy. Improvement is seen in the drug therapy's first four to six weeks. After that, however, it takes four to 12 weeks to eliminate the organisms.

• In rare cases, surgical removal of the infected portion of the lung is performed if antibiotics fail to work.

How to Prevent Mac Lung Disease?

• A vent system should be used in the bathroom and kitchen to exhaust the steam.

• A mask should be used while working in the garden.

• Working in a dust environment should be avoided.

• Lifetime prophylactic treatment with macrolide antibiotics like Azithromycin is given to patients with AIDS to prevent MAC infection.

Conclusion

MAC is a group of Mycobacteria that causes noncontagious respiratory infections. MAC lung disease is a curable respiratory disorder. It can cause serious and life-threatening respiratory complications. It causes irreversible lung damage. It usually affects immunocompromised individuals. Antibiotic treatment is required for more than one year to cure this infection. Early diagnosis and treatment help prevent the disease's progression and the risk of complications.