Pulmonary capillaritis in monozygotic twin boys

Pulmonary hemorrhage can be classified as either proximal or distal (alveolar). Causes of proximal hemorrhage include infection, foreign body aspiration, pulmonary embolus, trauma, vascular malformation, and pulmonary hypertension. Causes of distal or diffuse alveolar hemorrhage are divided by the histologic presence or absence of capillaritis, which is characterized by inflammation of the alveolar interstitium and pulmonary capillary structure. Pulmonary capillaritis is a rare event in children and is associated with higher morbidity and mortality than diffuse alveolar hemorrhage without capillaritis. This is a report of 17-month-old previously healthy monozygotic twins presenting simultaneously with diffuse alveolar hemorrhage, pulmonary capillaritis, and an otherwise negative serologic workup. This suggests a role of genetic predisposition in this rare disease.