Idiopathic pulmonary fibrosis: multiple causes and multiple mechanisms?

Idiopathic pulmonary fibrosis (IPF) is a devastating condition that carries a prognosis worse than that of many cancers. A recent classification of the idiopathic interstitial pneumonias has redefined the diagnostic criteria necessary to determine a diagnosis of IPF. The present authors believe that this redefinition is incorrect, relying as it does on subtle histological differences for the definition of separate disease categories. A further issue affecting IPF research is the polarisation of views around two competing pathogenetic hypotheses. One argues for the primacy of inflammation as the trigger that initiates fibrosis, and the other proposes that fibrosis arises as a consequence of chronic epithelial injury and failure of repair due to aberrant epithelial-mesenchymal interactions. The present authors believe that this schism is hampering understanding of IPF and skewing research priorities. It is argued here, instead, that abnormalities in multiple pathways involved in wound healing and inflammation lead to the development of idiopathic pulmonary fibrosis, and it is suggested that a new rationale for clinical classification and pathogenesis may be more productive in driving the search for novel therapies in the future.