A Challenging Diagnosis of Febrile Pancytopenia in a Patient With a History of Autoimmune Disease.

Pancytopenia is a hematologic condition characterized by a decrease in all three peripheral blood cell lines. There are many causes of pancytopenia, and the proper approach is required for accurate diagnosis. Brucellosis and systemic lupus erythematosus (SLE) are both diseases that can initially present as pancytopenia, both of which require a targeted workup to diagnose. Due to the immune system's complexity, many distinct diseases may have similar symptomatology. Furthermore, infections and rheumatological diseases can stimulate the same molecular pathways and trigger T and B cells. This creates a cross-reactivity between microbial peptides and self-peptides, allowing the spread of microbial-specific T cells that can also respond to self-peptides. Brucellosis has broad clinical manifestations, often mimicking many other diseases, such as rheumatoid arthritis, sarcoidosis, and SLE. In addition, brucellosis-induced autoantibody production has been described as a triggering factor for immunologic reactions, elevating rheumatological markers by a poorly understood mechanism. Finally, SLE is a well-known medical condition that can mimic several medical conditions, including brucellosis.  We present a case of a young patient who was admitted with febrile pancytopenia. The patient also had IgM antibodies positive for brucellosis and high immune markers for SLE. She was treated for both diseases, and afterward, in retrospect, it was confirmed that the patient did not have acute brucellosis.