Group 1’: Pulmonary veno-occlusive disease and/or pulmonary capillary hemangiomatosis
PVOD and PCH are uncommon conditions, but they are increasingly recognized as causes of PH [53]. A recent clinicopathologic study [54] analyzed specimens from 35 patients diagnosed as having either PVOD (n = 30) or PCH (n = 5). PCH was identified in 24 (73%) cases diagnosed as PVOD. Indeed, venous involvement was present in 4/5 cases initially diagnosed as PCH. These findings suggest that PCH may be an angioproliferative process frequently associated with PVOD. Similarities in pathologic features and clinical presentation suggest that these disorders may be two different presentation of the same disease [54].
Although PVOD and PCH may present similarly to idiopathic PAH, there are a number of important differences. These include the presence of crackles on examination, radiologic abnormalities on high-resolution computed tomography of the chest (ground glass opacities, septal thickening, mediastinal adenopathy) [55-58], hemosiderin-laden macrophages on bronchoalveolar lavage [59], and a lower DLCO and PaO2 in patients with PVOD or PCH [58]. PVOD/PCH remains a difficult disorder to categorize, as it shares characteristics with idiopathic PAH but also has a number of distinct differences. Given the current evidence, it was decided that PVOD/PCH should be a distinct category but not completely separated from PAH and PVOD/PCH are designated as 1’ in the current classification.