ASTHMA

Relationship between induced sputum eosinophils and the clinical pattern of childhood asthma

P G Gibson¹, J L Simpson¹, R Hankin², H Powell¹, R L Henry³

¹ Department of Respiratory and Sleep Medicine, and Hunter Medical Research Institute, John Hunter Hospital, Newcastle, 2310 NSW, Australia
² The John Hunter Children’s Hospital, Newcastle, 2310 NSW, Australia
³ School of Women’s and Children’s Health, The University of New South Wales, Randwick, 2031 NSW, Australia

Correspondence to:
Correspondence to:
A/Prof P G Gibson, Department of Respiratory and Sleep Medicine, John Hunter Hospital, Locked Bag 1, Hunter Region Mail Centre, NSW 2310, Australia; mdpgg{at}mail.newcastle.edu.au

Background: The relationship between the clinical pattern of asthma and airway inflammation in childhood asthma is poorly characterised, yet underpins the treatment recommendations in current asthma guidelines. A study was undertaken to examine the relationship between airway inflammation and clinical asthma in children.

Methods: Children with asthma (n=146) and healthy controls (C, n=37) were recruited from primary and specialist clinics. Sputum induction and hypertonic saline challenge were performed.

Results: As the frequency of asthma episodes in the past 12 months increased, there were significant increases in sputum eosinophils (median; infrequent episodic (IE) 1.5%, frequent episodic (FE) 2.3%, persistent (P) 3.8%, control (C) 1.0%; p=0.002), sputum eosinophil cationic protein (ECP) (IE 113 ng/ml, FE 220, P 375, C 139; p=0.003), and desquamated bronchial epithelial cells (IE 2.0%, FE 6.0%, P 5.0%, C 2.5%; p=0.04). Treatment intensity was also associated with increased sputum eosinophils (p=0.005). The relationships between other severity markers (current symptoms, lung function) were less strong.

Conclusion: Children with more frequent episodes of clinical asthma exhibit increasing airway inflammation that is characterised by sputum eosinophilia and bronchial epithelial desquamation. The results support clinical assessment by frequency of wheezing episodes over the past 12 months when determining anti-inflammatory treatment requirements, and indicate that current symptoms are determined by mechanisms in addition to sputum eosinophilia.

Keywords: asthma; children; induced sputum; eosinophil

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