Diffuse alveolar hemorrhage: An underreported complication of transplant associated thrombotic microangiopathy.

Hematopoietic stem cell transplantation-associated thrombotic microangiopathy (TA-TMA) and diffuse alveolar hemorrhage (DAH) are well recognized post-transplant complications that carry a high risk of mortality; however, the risk of DAH complicating the course of transplant patients with TA-TMA is not well understood. We conducted a ten-year retrospective study at our institution to determine the incidence of DAH in a cohort of pediatric patients with TA-TMA and described their presentation and outcomes. Additionally, autopsy slides, when available, were reviewed to assess for histological evidence of microvascular injury and alveolar hemorrhages. A total of 58 pediatric patients with TA-TMA were identified. Of these, 14 (24%) had DAH. Majority of DAH cases occurred within a week of TA-TMA diagnosis (n = 8, 57%, range 0-698 days). Mortality was 100% for patients with DAH and TA-TMA. Infections were found to be a significant risk factor for DAH in TA-TMA. Autopsy was performed in 11 of the 14 patients, and pulmonary slides were available for review in ten cases. 70% cases had pathological evidence of microvascular injury, concerning for pulmonary TA-TMA. We conclude that DAH is a potentially fatal complication in patients with TA-TMA and may be a result of pulmonary microangiopathy.