The term “brittle asthma” was first used in 1977 to describe patients with asthma who maintained a wide variation in peak expiratory flow (PEF) despite high doses of inhaled steroids.1 It was coined at a time when patterns of PEF variability were beginning to be described with respect to clinical patterns of disease, such as the morning dip in PEF1 ,2and the “double dip” pattern of morning and evening dips3 seen in patients with less well controlled asthma. The brittle asthmatic PEF pattern of variability was identified as a separate group, being described as chaotic showing no such obvious repeating pattern. The significance of the brittle pattern was not completely clear at that time, although the inference was that these patients had more severe asthma that was, by definition, more difficult to control. Three papers published shortly afterwards showed that this chaotic pattern of PEF could lead to death from an acute severe attack4-6 and the authors raised the possibility that these patients tended to be poorly compliant with treatment. Nevertheless, not all non-compliant patients showed this chaotic pattern, so clearly other factors were important. However, it is not clear how these patients would fit into a classification of severe asthma which would include all those patients at risk of death or repeated hospital admissions.

Some physicians are unhappy with brittle asthma being classified as a separate asthma phenotype, regarding these patients as simply the severe end of the spectrum. However, it is our belief that definition of differing asthma phenotypes is important, so what follows represents our view that brittle asthma should be considered as a specific asthma phenotype. We suggest how further study of patients of this type may help in unravelling the pathogenesis and treatment of at risk asthma.