Febrile Neutropenia as the First Manifestation of T-Cell Large Granular Lymphocytic Leukemia

T-cell large granular lymphocytic (T-LGL) leukemia is a rare lymphoproliferative disorder, characterized by peripheral blood and bone marrow infiltration with large granular lymphocytes (LGL), splenomegaly, cytopenias, and a frequent association with autoimmune diseases. Recurrent bacterial infections due to neutropenia are the main reason why patients come to medical attention. Despite not being a curable disease, T-LGL leukemia usually has an indolent course, with deaths mainly resulting from severe infections. Treatment is often not required, however, when needed, aims to relieve symptoms, and reduce infections and transfusion needs.We describe a case of an 86-year-old female patient with febrile neutropenia, diagnosed with T-LGL leukemia after the resolution of infection and exclusion of other causes of neutropenia. A "watch and wait" approach was established after a multidisciplinary discussion.This case shows a frequent presentation of a rare disease, as well as the approach from diagnosis to treatment, reminding clinicians that T-LGL leukemia should be considered in the differential diagnosis of adults with febrile neutropenia.