In this study, the researchers were able to classify 88 percent of the 187 lung biopsy cases, and found a diverse spectrum of lung diseases that are largely unique to young children.

One-quarter of the lung diseases studied were grouped together under the label “growth abnormalities.” The best-known is pulmonary hypoplasia, in which prenatal conditions result in deficient lung growth. Another group of diseases was categorized as “surfactant dysfunction disorders,” which refer to genetic abnormalities of surfactant, a fluid, detergent-like substance that plays a critical role in keeping the air sacs of the lungs open.

Dr. Deutsch said that at Cincinnati Children’s Hospital and the other medical centers that participated in the study, the new classification system is helping pathologists diagnose children’s lung disease more accurately, leading in some cases to more appropriate treatment.

For instance, in the past, children with lung growth abnormalities might have been treated as though they had ILD and given steroids, which may not be an effective treatment for them.

The new system also gives doctors more information about an infant’s prognosis. In the past, children with ILD were thought to have a high rate of illness and death. The classification system can help doctors distinguish certain children who may appear very ill, but who have a high chance of recovery (such as children with pulmonary interstitial glycogenosis and neuroendocrine cell hyperplasia of infancy), from those with a particular genetic mutation, known as ABCA3, who are unlikely to recover on their own and may need a lung transplant, Dr. Deutsch said.

“This new system gives clinicians, radiologists and pathologists a structure upon which to base diagnoses in a uniform fashion —we’ll all be reading from the same book,” said Andrew Nicholson, M.D., consultant histopathologist at Royal Brompton Hospital and professor of respiratory pathology at the National Heart and Lung Institute Division of Imperial College School of Medicine in London, who co-authored an editorial accompanying the study with Andrew Bush, M.D.

“The next step is for researchers at other medical institutions and in other countries to test the new system to see how applicable it is to their patients,” Dr. Nicholson said. “Pathologists should review other cohorts of cases to see if any disease groups are missing, or if others are over-divided.”

“When a classification system for adult diffuse lung disease was proposed by the American Thoracic Society and European Respiratory Society in 2002, pathologists took part in such a validation process,” he said. “Before the adult classification system was in place, doctors sometimes used the same term for different diseases, but since 2002, we have been able to use much stricter definitions, which has improved accuracy of diagnosis.”

It has also improved physicians’ understanding of some disease patterns that were previously viewed as idiopathic. “The new classification for infant lung disease gives us the same opportunity to tighten our definitions and increase the accuracy of diagnosis in children,” said Dr. Nicholson.