Interstitial Pneumonia in Patients with Idhiopatic Thrombocytopenic Purpura.

INTRODUCTION: Idhiopatic thrombocytopenic purpura (ITP) is an autoimmune disease characterized by a premature destruction of platelets by macrophage, especially in the spleen. However in some cases, platelet sequestration and destruction may occur in other organs. Chromium labeled platelet sequestration study revealed that liver or precordial area are prominent sites of sequestration in some cases, suggesting that the lung might be the site in certain cases. Some cases of interstitial pneumonia are associated with immunologic injury to the lung and seen in patients with some autoimmune diseases, infections, drugs and transfusion related acute lung injury (TRALI) in which transfusions of platelets and blood products induce acute lung injury due to sequestration of platelets and neutrophils in lungs, sometimes leading to ARDS. We describe here an unusual association between ITP and interstitial pneumonia, suggesting that a lung injury similar to TRALI is involved in acute and recurrent ITP. METHODS: We have identified patients with ITP who developed interstitial pneumonia during the course of ITP. We reviewed their charts and analyzed their clinical courses of ITP and interstitial lung diseases. Laboratory tests and chest X ray or CAT scans were reviewed. The laboratory study included CBC, platelets and platelets activation was measured by PMP (platelet microparticles), expression of CD62p flowcytometrically. RESULTS: We have identified 6 patients with ITP who developed interstitial pneumonia during the course of ITP. In two of six, interstitial pneumonia was detected at the presentation of acute ITP. ITP was severe with platelet counts less than 10.000. Interstitial pneumonia was discovered incidentally by chest X ray and confirmed by CAT scans. A mild symptom of dyspnea was detected in careful examination. One underwent lung biopsy which showed findings consistent with brochiolitis obliterans organizing pneumonia. Repeated CAT scans in 1–3 months revealed marked improvement but residual interstitial infiltrates still persisted. Four others had a long standing chronic ITP with clinical courses characterized by frequent relapses in spite of surgical and medical therapy. Four of six patients had splenectomy. Interstitial lung diseases were detected at the time of a severe relapse with platelet counts of less than 20.000. One patient underwent chromium labeled platelet sequestration study which revealed rapid sequestration of platelets in the lung. Interstitial infiltrates improved following improvement of ITP but two progressed to interstitial pulmonary fibrosis. CD62P measured by flowcytometry was very high in all 3 patients tested, indicating persisting platelet activation in this clinical setting. SUMMARY: We report interstitial pneumonia developing in 6 patients with ITP. Clinically all were asymptomatic and detection of interstitial pneumonia was incidental radiology finding. A mild symptom of exertional dyspnea was present in careful investigation. Chest X ray or CT scans showed nonspecific interstitial infiltrates and showed an overall improvement within months but residual infiltrates persisted. Two progressed to pulmonary fibrosis. We suggest that platelets are sequestered and destroyed in the lung in some patients with ITP, to generate cytokines and lipid mediators that lead to a nonspecific interstitial lung disease.