Phenotypes of idiopathic pulmonary arterial hypertension

We read with great interest the registry analysis by Marius M Hoeper and colleagues suggesting that patients with idiopathic pulmonary arterial hypertension (IPAH) and a lung phenotype defined by a lung diffusion capacity for carbon monoxide (DLCO) of less than 45% of the predicted value and a smoking history have a worse prognosis than do patients with more classical IPAH. But what is the exact meaning of classical IPAH now? As a crude estimate, some 15–30% of the patients would have presented with a lung phenotype. The lung phenotype of IPAH might be three times more common in some registries than in others. Thus, further studies might be needed to better define the lung phenotype of IPAH and its pathophysiology. Another intriguing aspect of the report by Hoeper and colleagues is that more than half of their patients with classical IPAH achieved a low risk status at follow-up, whereas most (67%) of them were on only one targeted therapy. In the Italian Pulmonary Hypertension network, this good result was achieved in only 31% of the patients with IPAH.