Is the bronchiectasis severity index applicable to cystic fibrosis (CF) bronchiectasis?

Does the Bronchiectasis Severity Index Apply to Cystic Fibrosis Bronchiectasis?

No, the Bronchiectasis Severity Index (BSI) should not be used for cystic fibrosis (CF) bronchiectasis, as it was specifically developed and validated only for non-cystic fibrosis bronchiectasis, with CF patients explicitly excluded from the validation studies. 1

Key Evidence Against Using BSI in CF

Development and Validation Excluded CF Patients

• The BSI was designed to predict future exacerbations, hospitalizations, health status, and death over 4 years specifically in non-CF bronchiectasis patients 1
• Patients with CF were explicitly excluded from the BSI development and validation cohorts 1
• The FACED score, another severity scoring system for bronchiectasis, was similarly developed using only non-cystic fibrosis bronchiectasis patients 2

CF is Managed as a Distinct Clinical Entity

• The British Thoracic Society guidelines explicitly state that "cystic fibrosis (CF) bronchiectasis is managed as a distinct clinical entity" 1
• CF has established disease-specific guidelines and management protocols that differ fundamentally from non-CF bronchiectasis 1, 3
• Treatment responses in CF bronchiectasis differ from non-CF bronchiectasis, necessitating separate clinical guidance 1

Why CF Bronchiectasis Differs

Distinct Pathophysiology

• CF bronchiectasis results from CFTR dysfunction causing impaired mucociliary clearance, chronic infection, and progressive structural lung damage 3
• CF patients have specific complications including pancreatic exocrine insufficiency (85%), CF-related diabetes (20% of adolescents, 40-50% of adults), and CF-related liver disease (20-40%) that are not captured in BSI scoring 3

Different Clinical Characteristics

• CF patients typically present with earlier disease onset, upper lobe predominance, and characteristic microbiology (Staphylococcus aureus, then Pseudomonas aeruginosa) 1
• Children with CF actually have better lung function than those with non-CF bronchiectasis (FEV1 94.5% vs 78.6% predicted), despite similar age and sex 4
• CF patients receive more intensive multidisciplinary care with more frequent respiratory physician and physiotherapy visits compared to non-CF bronchiectasis patients 4

Clinical Implications

Use CF-Specific Assessment Tools

• CF has its own validated outcome measures, including the revised Cystic Fibrosis Questionnaire respiratory symptoms scale (CFQ-R RSS) 5
• CF-specific CT scoring systems (CF-CT scoring system) exist to quantify bronchiectasis and trapped air, which correlate with quality of life and predict pulmonary exacerbations 5

Management Differences

• CF patients require specialized multidisciplinary care at tertiary centers with CF-specific protocols 3, 4
• Treatment approaches differ significantly—for example, recombinant human DNase (rhDNase) is beneficial in CF but should NOT be used in non-CF bronchiectasis 6
• CF management includes CFTR modulator therapy, pancreatic enzyme replacement, and CF-specific nutritional support not applicable to non-CF bronchiectasis 3

Common Pitfall to Avoid

Do not assume that severity scoring systems validated in non-CF bronchiectasis can be extrapolated to CF patients. The BSI incorporates variables like age, BMI, hospitalization history, and exacerbation frequency 1, but these parameters have different prognostic significance in CF due to the underlying genetic disease, earlier age of onset, and fundamentally different disease trajectory. Using BSI in CF patients would provide misleading severity assessments and potentially inappropriate management decisions.