en Hematology Hematology case report case report <span style="font-size:14px;"><span style="font-family:Times New Roman;"><span style="color:#0000ff;"><strong><em>Background</em></strong><em>:</em> </span>Hemophagocytic lymphohistiocytosis (HLH) is a rare disease with different causes. HLH has been categorized into two sub-groups; primary HLH which is associated with some gene mutations and secondary HLH that is developed by various causes, such as autoimmune disease, infections, and malignancies. However, the symptoms of both groups are identical and if left untreated, it will result in death.<br> <span style="color:#0000ff;"><strong><em>Case Presentation</em></strong><em>:</em></span> In this study, we reported a 39 years old man had symptoms such as fever, weakness and chill for a month period of time. Firstly, due to pancytopenia in peripheral blood findings and clinical manifestations, he had been diagnosed with myelodysplastic syndrome (MDS) with an excess blast but the elevated liver enzymes and bilirubin were not consistent with this diagnosis. Hence, we recommended more investigation such as CT scan, bone marrow aspiration and bone marrow biopsy with immunohistochemistry tests. Finally, we found macrophages and histiocyte in bone marrow biopsy smear with Wright-Giemsa staining that engulfed the cells such as platelets and lymphocytes, so HLH syndrome was confirmed and treatment program with latest approved protocols started for the patient.<br> <span style="color:#0000ff;"><strong><em>Conclusion</em></strong><em>:</em> </span>HLH syndrome is a life-threatening disease that can be saved if timely diagnosed. Therefore, more consideration of all the laboratory findings and clinical signs of the patient can help to diagnose the disease more accurately. Also, we did a review of its pathophysiology, symptoms and therapeutic treatments.</span></span> Hemophagocytic Lymphohistiocytosis, Splenomegaly, Fever 439 443 http://caspjim.com/browse.php?a_code=A-10-1854-1&slc_lang=en&sid=1 Majid Gholizadeh majid_gh2014@yahoo.com 100319475328460031219 100319475328460031219 No Hematopoietic Stem Cell Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran Shirin Kianersi ShirinK2011@gmail.com 100319475328460031220 100319475328460031220 No Hematopoietic Stem Cell Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran Leila Noorazar l.noorazar@sbmu.ac.ir 100319475328460031221 100319475328460031221 No Hematopoietic Stem Cell Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran Vahid Kaveh m.embryo2020@yahoo.com 100319475328460031222 100319475328460031222 No Firouzgar Hospital, Iran University of Medical Sciences, Tehran, Iran Elham Roshandel elham.roshandel@gmail.com 100319475328460031223 100319475328460031223 No Hematopoietic Stem Cell Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran Sina Salari s.salari@sbmu.ac.ir 100319475328460031224 100319475328460031224 Yes Hematopoietic Stem Cell Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran