Does Mycobacterium avium complex (MAC) cause bronchiectasis or do bronchiectatic lungs usually develop Mycobacterium avium complex (MAC) infection?

From the Guidelines

Bronchiectasis usually develops first and creates conditions favorable for Mycobacterium avium complex (MAC) infection, rather than MAC infection causing bronchiectasis in individuals with healthy lungs. This is based on the evidence from the study published in Chest in 2006 1, which suggests that MAC infection is the primary disorder that leads to progressive airway damage and bronchiectasis in certain patients. The study highlights that patients with typical clinical and radiographic features of MAC infection often have bronchiectasis and nodular densities, especially in the middle lobe and lingula.

Key Points to Consider

• Bronchiectasis is characterized by permanent widening of airways, mucus accumulation, and impaired clearance mechanisms, creating an environment where MAC bacteria can colonize and thrive.
• People with pre-existing bronchiectasis from conditions like cystic fibrosis, primary ciliary dyskinesia, or previous severe respiratory infections are at higher risk for developing MAC infections.
• Once established, MAC infection can worsen existing bronchiectasis through inflammatory damage, creating a cycle where the infection and bronchiectasis exacerbate each other.
• Treatment typically involves a multi-drug regimen including macrolides (clarithromycin or azithromycin), ethambutol, and rifampin for 12-18 months after culture conversion, along with airway clearance techniques to manage the bronchiectasis, as recommended by the guidelines published in the European Respiratory Journal in 2005 1.

Management of Bronchiectasis and MAC Infection

• The management of bronchiectasis involves periodic evaluation of bronchial colonisation patterns, sputum cultures, and antibiotic treatment directed towards the colonising bacterial flora.
• The use of antibiotics with good bronchial penetration and the ability to decrease bacterial burden is recommended, as well as the use of antimicrobials active against H. influenzae empirically.
• In cases of risk factors for P. aeruginosa, ciprofloxacin is the best oral anti-pseudomonal agent, and combinations of antibiotics may be advisable.

From the Research

Relationship Between MAC and Bronchiectasis

• MAC lung disease can manifest as bronchiectasis with nodular and reticulonodular radiographic changes, termed "nodular bronchiectatic (NB) MAC lung disease" 2.
• The priorities for patients with NB MAC lung disease are to treat the underlying bronchiectasis and determine the course and impact of the MAC infection over time 2.
• Bronchiectasis is often present in patients with MAC lung disease, and airway clearance measures for bronchiectasis are frequently the initial treatment effort 3.

Development of MAC in Bronchiectatic Lungs

• There is no clear evidence to suggest that MAC directly causes bronchiectasis, but rather that bronchiectasis can provide a fertile ground for MAC infection to develop 2, 3.
• The relationship between MAC and bronchiectasis is complex, and it is often difficult to determine which condition developed first 3.
• Treatment of MAC lung disease often involves addressing the underlying bronchiectasis, and guidelines-based MAC therapy with multidrug regimens including macrolides is usually effective 2, 4, 5, 6.

Treatment of MAC Lung Disease with Bronchiectasis

• Treatment of patients with MAC lung disease and bronchiectasis requires a comprehensive approach, including airway clearance measures, antimycobacterial therapy, and management of underlying conditions 2, 3.
• Intermittent antibiotic therapy, including azithromycin and ethambutol, may be an effective treatment regimen for noncavitary MAC lung disease with bronchiectasis 5, 6.
• Clinicians must be familiar with MAC drug resistance mechanisms and the importance of avoiding development of macrolide resistance due to inadequate therapy 2, 3.