(478) A Unique Case of Hemophagocytic Lymphohistiocytosis Secondary to Mixed Connective Tissue Disease

Introduction: Haemophagocytic lymphohistiocytosis (HLH) is a rare hyperinflammatory syndrome that can progress to multi-organ failure and death. Typically triggered by a viral illness, malignancy, or an autoimmune condition, patients often present with nonspecific symptoms. A timely diagnosis and initiation of immunosuppressives is paramount to survival. We present a case of a young female with newly diagnosed mixed connective tissue disease (MCTD)-associated myopericarditis and HLH.

Description: A 20-year-old woman with no prior medical history presented to our hospital with chest pain. A cardiac workup revealed diffuse ST-segment elevations on electrocardiogram, elevated troponin consistent with myopericarditis. Echocardiography showed preserved ejection fraction and no structural abnormalities. Despite anti-inflammatory therapy, the patient declined rapidly with persistent fevers, cytopenias, progressive renal failure necessitating hemodialysis. An autoimmune evaluation revealed the presence of anti-nuclear and anti-U1-ribonucleoprotein antibodies and low complement levels suggestive of undiagnosed MCTD. Despite a trial of intravenous corticosteroids, the patient progressed rapidly to multi-organ failure. Further laboratory evaluation revealed hemoglobin of 8.1 g/dL, platelet count of 90 x10 x10^3/uL, triglycerides of 447 mg/dL, and a ferritin value of 57,000 ng/mL. A bone marrow biopsy revealed hemophagocytic histiocytes. With the persistent fever, lab abnormalities, and bone marrow pathology, the patient met five out of eight criteria needed for diagnosis per the HLH-2004 protocol. The patient was swiftly started on immunosuppressives, and once hemodynamically stable, was transferred to a tertiary facility where she underwent a hematopoietic stem-cell transplant.

Discussion: We outlined and unusual case as myopericarditis is an atypical manifestation of MCTD (PMID: 16218472). Furthermore, HLH occurring in the course of rheumatic disease is an important and often undiagnosed clinical entity (PMID 23104659). The multi-organ system involvement and diagnostic overlap between MCTD and HLH is obscure and can affect prognosis. To our knowledge, this is the third case of HLH related to MCTD and hope it provides insight towards early recognition and management of HLH.