The value of classifying interstitial pneumonitis in childhood according to defined histological patterns

Aims: Interstitial pneumonitis in children is very rare and most cases have been classified according to their counterparts in adults, although the term 'chronic pneumonitis of infancy' has recently been proposed for a particular pattern of interstitial lung disease in infants. We reviewed our paediatric cases of interstitial pneumonitis, first, to look at the spectrum of histological patterns found in this age group and, second, to determine whether the classification of such cases in childhood is both appropriate and worthwhile. Methods and results: Twenty-five of 38 open lung biopsies showed an overlapping spectrum of interstitial pneumonitis, including three cases that fulfilled the histological criteria for chronic pneumonitis of infancy. There were 11 cases of reactive pulmonary lymphoid hyperplasia (either lymphoid interstitial pneumonitis or follicular bronchiolitis), five of which were associated with abnormalities of the immune system. Four cases were classified as desquamative interstitial pneumonitis and the remaining seven cases were classified as nonspecific interstitial pneumonitis. There were no cases with the histological features of usual interstitial pneumonitis. Most patients responded to steroids but tended to have a residual deficit in lung function. Mortality appeared to be associated with presentation at a young age. Conclusion: Classification of interstitial pneumonitis according to their adult counterparts is appropriate for this younger age group and can provide valuable information for the clinician. The term 'chronic pneumonitis of infancy' refers to a specific histological pattern, but whether it represents a separate disease or a reflection of pulmonary immaturity remains to be proven.