What causes cystic bronchiectasis distributed mainly at the central airways?

Causes of Cystic Bronchiectasis with Central Distribution

Cystic bronchiectasis with predominantly central distribution is most commonly caused by allergic bronchopulmonary aspergillosis (ABPA), followed by cystic fibrosis, primary ciliary dyskinesia, and chronic Mycobacterium avium complex infection. 1, 2

Primary Causes of Central Cystic Bronchiectasis

Allergic Bronchopulmonary Aspergillosis (ABPA)

• ABPA is characterized by immune-mediated inflammation in response to inhaled Aspergillus fumigatus antigen, causing central bronchiectasis (inner two-thirds of chest on CT scan) 1
• Essential diagnostic criteria include:
  • Central distribution of bronchiectasis
  • Asthma
  • Immediate cutaneous reactivity to Aspergillus antigen
  • Elevated total serum IgE level (> 417 IU/L or 1,000 ng/mL)
  • Elevated serum levels of IgG-A fumigatus or IgE-A fumigatus 1
• Associated findings may include mucoid impaction of bronchi and bronchocentric granulomatosis 1

Cystic Fibrosis (CF)

• CF is one of the most common identifiable causes of bronchiectasis in the United States and Europe, occurring in 1 per 2,000-3,000 live births 1
• Caused by mutation of the gene encoding the CF transmembrane regulator protein, disrupting normal fluid and electrolyte flow across cell membranes 1
• Results in excessive and tenacious mucus secretion, impaired mucus transport, and bronchial dilation 1
• Isolation of mucoid strains of Pseudomonas in sputum is considered a marker of CF, though it can occur in other conditions 1

Primary Ciliary Dyskinesia (PCD)

• Genetic disorder affecting ciliary structure and function, leading to impaired mucociliary clearance 1
• Causes recurrent sinopulmonary infections and bronchiectasis, often with central distribution 1
• Haemophilus influenzae is the most common bacterial isolate in sputum, but Pseudomonas isolates are also common 1

Mycobacterium Avium Complex (MAC) Infection

• MAC infection can cause a clinicopathologic subtype of chronic pulmonary infection predominantly in white women in their seventh or eighth decade (Lady Windermere syndrome) 1
• Radiographs and CT scans show bronchiectasis and nodular densities, especially in the middle lobe and lingula 1
• The nodules are typically distributed around peripheral vessels and airways, often with a tree-in-bud configuration 1
• MAC infection can be the primary disorder leading to progressive airway damage and bronchiectasis 1

Other Potential Causes

Immunodeficiency Disorders

• Congenital and acquired hypogammaglobulinemia (especially IgG and/or IgG subclasses) 1
• HIV infection can predispose to bronchiectasis 1, 3
• Common variable immunodeficiency may require Ig replacement therapy 1

Autoimmune Conditions

• Rheumatoid arthritis (up to 3% of patients have symptomatic bronchiectasis, and up to 30% have HRCT-diagnosed disease) 1
• Inflammatory bowel disease, especially chronic ulcerative colitis 1

Congenital Disorders

• Alpha-1-antitrypsin deficiency 1
• Tracheobronchomegaly (Mounier-Kuhn syndrome) 1
• Cartilage deficiency (Williams-Campbell syndrome) 1
• Young syndrome 1

Traction Bronchiectasis

• Caused by contractile force of surrounding fibrotic lung tissue, which exerts traction and expands the diameter of involved airways 4
• Associated with idiopathic pulmonary fibrosis and other fibrotic lung diseases 4
• Characterized by irregular bronchial dilation in areas of pulmonary fibrosis 4

Diagnostic Approach

• High-resolution CT (HRCT) scanning is the diagnostic procedure of choice to confirm bronchiectasis, with sensitivity and specificity exceeding 90% 1, 2
• Key features on HRCT include:
  • Enlarged internal bronchial diameter (signet ring sign)
  • Failure of larger airways to taper while progressing to the lung periphery
  • Air-fluid levels in dilated airways 1
• In patients with suspected bronchiectasis, a systematic search for underlying causes should be performed as it may lead to treatment that can slow or halt disease progression 1

Clinical Implications and Management

• Early diagnosis and intervention are important to potentially reverse bronchial wall dilatation in early disease 2
• Treatment should target the underlying cause when identified 1, 3
• Management may include long-term antibiotic therapy, airway clearance techniques, and treatment of exacerbations 2, 3
• For ABPA, corticosteroid treatment may be beneficial 1
• For MAC infection, treatment with a macrolide, ethambutol, and a rifamycin is considered first-line therapy for patients with severe or progressive symptoms 1

When evaluating a patient with cystic bronchiectasis with central distribution, clinicians should prioritize investigation for ABPA, cystic fibrosis, primary ciliary dyskinesia, and MAC infection, as these are the most common causes with this specific distribution pattern.