Science and Education Publishing American Journal of Medical Case Reports 2 12 2014 12 10 Isolated Protein S Deficiency Presenting as Thromboembolic Pulmonary Arterial Hypertension in a Young Child 283 287 EN Krishna Kumar Yadav Department of Pediatrics, King George's Medical University, Lucknow, India S N Singh Anit Parihar Department of Pediatrics, King George's Medical University, Lucknow, India AJMCR20142127 10.12691/ajmcr-2-12-7 2014 09 27 2014 12 04 2014 12 10 A 13 months male child presented with progressive dyspnea of three months and recent cyanosis. Cardio-respiratory examination revealed tachypnea, cyanosis, left parasternal heave and loud P2. Echocardiography revealed thrombus in pulmonary artery and severe pulmonary arterial hypertension. Tests for throbmophilia demonstrated protein S deficiency. Treatment included anticoagulants, sildenafil, bosentan and supportive measures without embolectomy. The child get stabilized soon with echocardiographic evidence of thrombus resolution, however, tachypnea and oxygen dependency persisted. He discharged on bosentan, warfarin and home O2 inhalation. Follow-up CT pulmonary angiography showed organized thrombus in pulmonary artery and cystic lesions in lungs. During 14 months of follow-up he remained tachypneic and oxygen dependent despite discharge medication and additional sildenafil, and subsequently died of right ventricular failure and pulmonary hemorrhage. Thromboembolic pulmonary arterial hypertension due to protein S deficiency can present in early childhood and treatment with anticoagulants, bosentan and sildenafil without embolectomy may not be appropriate.