Pulmonary veno-occlusive disease. Entity or syndrome?

Pulmonary veno-occlusive disease is a rare and usually fatal condition in which there is gradual obliteration of the pulmonary veins and venules. Without a lung biopsy the clinical diagnosis of this disease is difficult. If there is pulmonary hypertension with roentgenographic signs of pulmonary edema and of congestion in the absence of signs of increased left atrial pressure, the diagnosis must be considered. The morphologic picture of the lungs is characteristic. The small veins, and sometimes also the major veins, are narrowed or occluded by fibrous tissue, almost certainly on the basis of organized thrombi. Nodular areas of congestion, interstitial fibrosis, and pneumonitis are regularly present. A viral etiology has been suggested in a number of cases. If we may assume, however, that thrombosis of pulmonary veins is the initial event, the possibility has to be considered that this may be elicited by a virus in some patients and by toxic factors or by clotting disorders in others. Pulmonary veno-occlusive disease might then well be a syndrome rather than an etiologic entity.