Recurrent and Refractory Hemophagocytic Lymphohistiocytosis in an Elderly. Role of Immune Aberration Due to Myeloid Gene Mutation

Hemophagocytic lymphohistiocytosis (HLH) is a potentially fatal hyper-inflammatory disease induced by aberrant immune activation and subsequent proliferation of macrophages, histiocytes and T-helper cells. In this abstract we present a case of HLH, which relapsed twice despite ongoing treatment, and we hypothesize on possible causes and mechanisms. A 77 year old female presented to our hospital with ongoing fevers and worsening cytopenia. Blood counts from three years before the current presentation showed Hb 120g/L, WBC 4.0 x 10^9/L, Neutrophil count 1.8 x 10^9/L, Lymphocytes count 1.8 x 10^9/L and Platelet count 104 x 10^9/L. A bone marrow examination at that time revealed a normocellular marrow with 28% lymphocytes of which70% were CD 4+, CD 3+, CD5+ and CD 7-. Molecular studies confirmed T cell receptor (TCR) gamma gene rearrangement. The karyotype on the bone marrow was normal. In the absence of clinical symptoms, the patient was regularly followed up without specific therapy. During the current admission, however, the patient was febrile, had progressive pancytopenia and biochemistry suggestive of HLH (Fig 1). She was extensively evaluated which ruled out infective and malignant causes. A bone marrow aspirate and biopsy was performed and treatment initiated as per HLH-94 protocol. The bone marrow examination showed marked features of haemophagocytosis on a normocellular background. A small clone of T-lymphocytes was again noted with similar features as in the first biopsy. In addition, a prominent population (10%) of promonocytes was apparent with an uncertain significance. Karyotype was normal. Next Generation Sequencing showed TET2 frame shift mutation at low variant allele frequency (5%). Patient responded well to treatment. While on tapering dose of steroids, the disease flared up (Fig 1) and the patient was restarted on high dose steroids with etoposide. After a quick initial response, while still on active treatment, she again relapsed within 3 weeks, coupled with sepsis and acute myocardial ischemia, followed by sudden death. We were unable to identify a cause for HLH. There were 10% promonocytes in bone marrow and evidence of aberrant T-cells on flow cytometry. Although there was no obvious evidence of dysplasia on microscopy, the flow cytometry showed up- regulation of CD 64 and CD 14, down regulation of CD13 and 11b, and CD 34 expression in granulocytes possible indicating dysplasia as per the Wells criteria. (Wells et al., Blood 2003; 102(