Background:Although the classical triad of thrombocytopenia, microangiopathic hemolytic anemia, and neurological changes has been well recognized, thrombotic thrombocytopenic purpura (TTP) sometimes presents with atypical clinical features. Some cases of acute respiratory distress syndrome (ARDS) were suspected to be a manifestation of TTP.Methods:We examined retrospectively the medical records of patients with known TTP from 1981 to 1998. The patients who developed ARDS simultaneously with TTP were identified. Clinical, laboratory, and other pertinent data were reviewed; the clinical outcome was documented.Results:Seven out of 56 patients with an established diagnosis of TTP were identified as having ARDS. All 7 patients had progressive dyspnea, persistent hypoxemia with diffuse pulmonary infiltrates, and no evidence of localized pneumonia, pulmonary emboli, congestive heart failure, or other identifiable lung diseases. In addition to ARDS, 4 patients developed progressive neurological (mental) changes, 3 developed fever, and 2 developed renal failure. Six patients were treated with ventilatory support in the ICU. Upon establishing the diagnosis of TTP, 6 patients were treated with exchange plasmapheresis (EP) and 1 patient with an infusion of fresh frozen plasma. Within 2 days of initiation of EP, 4 patients showed marked respiratory improvement; shortly thereafter, mechanical ventilation was ended. Complete and long-lasting remission was achieved in all 4 patients. Three patients died because of delayed diagnosis and untimely employment of EP.Conclusion:Life-threatening ARDS can be associated with TTP. It is recommended that all patients with ARDS and unexplained thrombocytopenia be evaluated for unrecognized TTP. Early recognition of ARDS associated with TTP and timely EP is critical to a favorable outcome.