Chronic Infectious/Inflammatory Bronchiolitis in Adults
Chronic infectious/inflammatory bronchiolitis in adults is a heterogeneous disorder affecting small airways (≤2mm diameter without cartilage) characterized by persistent inflammation, fibrosis, and architectural distortion of the bronchioles, resulting from infectious agents (bacterial more commonly than viral in adults) or inflammatory processes that lead to chronic cough, airflow limitation, and potential progression to obliterative disease.
Definition and Anatomic Basis
Bronchiolitis affects airways with an internal diameter of ≤2mm that lack cartilage in their walls 1. The condition involves variable amounts of cellular inflammation (lymphocytic, neutrophilic, eosinophilic, or granulomatous), fibrosis, and architectural distortion 1. In chronic forms, this inflammation persists and can progress to diffuse airway narrowing, distortion, or complete obliteration 2.
Pathophysiology
The pathogenesis involves inflammation, fibrosis, and architectural distortion of small airways occurring with or without mucous hypersecretion and bronchial hyperresponsiveness 1. The chronic inflammatory process leads to structural changes including airway wall thickening, bronchiolar edema, smooth muscle hypertrophy, and peribronchiolar fibrosis 3.
Clinical Presentation
Key Features to Identify:
- Chronic cough (often the presenting symptom)
- Incomplete or irreversible airflow limitation on spirometry
- Purulent secretions (in infectious forms)
- History of relevant exposures (toxic inhalants, occupational hazards, drugs)
- Underlying systemic disorders (connective tissue disease, inflammatory bowel disease, transplant status)
- Prior respiratory infections that failed to fully resolve
Diagnostic Approach
Essential Workup:
Comprehensive exposure history: smoking, occupational irritants, toxic fumes, drugs, biomass fuels 1
Pulmonary function testing: spirometry with bronchodilator, lung volumes, gas exchange 1
High-resolution CT (HRCT) with expiratory cuts 1:
- Direct signs: Dilation or airway wall thickening appearing as nodular branching (2-4mm) and linear branching "tree-in-bud" abnormalities
- Indirect signs: Air-trapping (mosaic attenuation on expiration), subsegmental atelectasis
- Critical caveat: Normal HRCT cannot rule out bronchiolar disease since resolution is limited to airways >2mm diameter
Bronchoscopy: Required to rule out infection and identify purulent secretions when more common causes of cough are excluded 1
Surgical lung biopsy: Indicated when clinical syndrome, physiology, and HRCT findings do not provide confident diagnosis 1
Common Pitfall:
Chest radiographs are often normal despite significant bronchiolar disease due to the anatomic location 1. Always proceed to HRCT when bronchiolitis is suspected.
Etiologic Classification
Infectious Bronchiolitis (Adults):
- Bacterial (more common than viral in adults) 1
- Viral (respiratory syncytial virus, influenza) 1
- Post-infectious sequelae
Inflammatory/Non-Infectious:
- Toxic/antigenic exposures (occupational dusts, fumes, gases)
- Drug-related
- Connective tissue disorders
- Inflammatory bowel disease 1
- Transplant-related (bronchiolitis obliterans syndrome)
- Cryptogenic forms
Treatment Approach
For Infectious Bacterial Bronchiolitis:
Prolonged antibiotic therapy improves cough and is recommended 1. This represents the most evidence-based intervention with substantial benefit.
For Toxic/Antigenic Exposure or Drug-Related:
Cessation of exposure or medication PLUS corticosteroid therapy for those with physiologic impairment 1.
General Principles:
- Therapy must be tailored to the specific cause or diagnosis 1
- Smoking cessation is mandatory for all patients 4
- Avoidance of ongoing exposures (occupational, environmental pollutants) 4
What NOT to Do:
For stable chronic bronchitis with cough, there is insufficient evidence to recommend routine use of antibiotics, bronchodilators, or mucolytics as means of relieving cough per se 4. These should only be used when proven safe and effective for specific etiologies.
Prognosis and Monitoring
The condition can contribute significantly to morbidity and mortality if it persists and progresses to diffuse airway narrowing, distortion, or complete obliteration 2. Any etiology chronic bronchiolitis that persists requires ongoing monitoring for progression to obliterative disease.
Key Monitoring Parameters:
- Serial spirometry to detect progressive airflow limitation
- Repeat HRCT to assess for progression of bronchiolar changes
- Assessment for development of bronchiectasis (a potential sequela) 2
Critical Distinctions
This condition differs from chronic bronchitis (defined as cough with sputum ≥3 months/year for 2 consecutive years) 4 in that it specifically involves small airways pathology with distinct radiographic and pathologic features. It also differs from acute bronchiolitis, which predominantly affects infants and children and is usually viral and self-limited.