Case report of acquired hemophagocytic lymphohistiocytosis associated with progression of monoclonal gammopathy of unknown significance (MGUS)

Background: Acquired hemophagocytic lymphohistiocytosis (HLH) is an aggressive hyperinflammatory syndrome. Without prompt diagnosis and proper treatment, it can be life-threatening. HLH is commonly present in the setting of other autoimmune disorders, infection, organ transplantation, and malignancy.  However, to our knowledge, HLH associated with monoclonal gammopathy of undetermined significance (MGUS) has not been reported.Case presentation: A 67-year-old woman with an extensive history of MGUS and renal transplant presented with progressive fatigue, weight loss, intermittent fevers, splenomegaly, and pancytopenia. Serum protein electrophoresis with immunofixation identified a new monoclonal protein IgG lambda and a rapidly increasing pre-existing free kappa light chain. A bone marrow biopsy revealed focal clusters of kappa restricted plasma cells which comprised less than 10\% of marrow cellularity. Skeletal survey was negative for osteolytic lesions. She was also free of any end-organ damage.  Histological examination showed a prominent increase in histiocytes and macrophages, many of which show erythrophagocytosis and lymphophagocytosis. Together with her clinical presentation along with a hyperferritinemia, a diagnosis of HLH was confirmed utilizing the criteria of the Histiocyte Society. The patient underwent a splenectomy. Prompt treatment with etoposide and high dose dexamethasone eventually stabilized the patient and resulted in a full recovery, which coincided with the disappearance of the serum monoclonal IgG lambda.Conclusions: This report reveals a novel association of HLH with the progression of MGUS. Familiarity with this syndrome and its association with other conditions is indicated to ensure prompt diagnosis and appropriate patient treatment.