Severe Anaplasmosis With Multiorgan Involvement in a Rheumatoid Arthritis Patient.

Anaplasmosis, caused by the tick-borne bacterium Anaplasma phagocytophilum, is an emerging infectious disease with a broad spectrum of clinical manifestations. Here, we present a case report of a 66-year-old Caucasian woman residing in Connecticut who exhibited severe anaplasmosis with multi-organ involvement. The patient, with a medical history of rheumatoid arthritis and hypothyroidism, presented with confusion, lethargy, fever, myalgia, generalized weakness, and poor appetite in May 2023. Laboratory investigations revealed pancytopenia, hyponatremia, elevated liver enzymes with mild hyperbilirubinemia, and lactic acidosis. A buffy coat smear analysis demonstrated basophilic intracytoplasmic inclusion bodies in the neutrophils, supporting the diagnosis of severe anaplasmosis. Prompt administration of doxycycline, the recommended treatment for anaplasmosis, was initiated. However, the patient subsequently developed acute respiratory distress syndrome (ARDS) necessitating heated humidified high-flow nasal cannula (HFNC) therapy. Anaplasma polymerase chain reaction (PCR) confirmed the presence of the bacterium in the patient's blood. Following doxycycline treatment, the patient demonstrated improvement in peripheral blood findings, resolution of ARDS, and complete neurologic recovery. This case underscores the potential severity and diverse clinical manifestations of anaplasmosis, highlighting the importance of early recognition, prompt diagnosis, and timely initiation of appropriate treatment to prevent severe complications and improve patient outcomes.