Fever of Unknown Origin and Atrial Fibrillation: A Case Report

Fever of unknown origin describes a temperature greater than 100.9°F which is present on multiple instances for a period over three weeks with no confirmed diagnosis despite a minimum of three outpatient visits, three days of inpatient testing, or one week of extensive outpatient testing. This diagnosis presents challenges in clinical management due to the unknown etiology. This case highlights a fever of unknown origin presenting with new-onset atrial fibrillation in a patient with no previous cardiac history. A 62-year-old Caucasian male presented to the ED with a nine-day history of intermittent fevers and chills. He returned from a rafting trip in North Carolina two weeks ago but reported no tick bites, animal encounters, or river water ingestion. Further evaluation was significant for an elevated white blood cell count and elevated inflammatory markers. Laboratory and radiologic testing for a wide array of infectious and malignant etiologies were unremarkable. Soon after hospital presentation, he developed a fever of 102.9°F with new onset palpitations and chest tightness due to atrial fibrillation. Episodes of atrial fibrillation continued for his seven-day hospital course with more severe symptoms in the evenings. He was administered broad-spectrum antibiotics and tested extensively with no definitive etiology. His fever curve downtrended with max temperatures below 100.9°F on hospital days six and seven with asymptomatic episodes of atrial fibrillation, prompting discharge. He continued to have low-grade fevers measured below 100.9°F for several days post-discharge with no associated symptoms, resulting in a diagnosis of fever of unknown origin following the 21st day. Fever of unknown origin is a clinical challenge, particularly in cases with no diagnosis discovered and cases with potentially life-threatening complications such as atrial fibrillation. This patient had multiple potential etiologies for his condition, but none had sufficient evidence for diagnosis, resulting in uncertainty regarding the ideal management. As a result, constant monitoring with supportive treatments and broad-spectrum antibiotics was utilized. These measures allowed for symptom remission and hospital discharge for outpatient follow-up. This case highlights a rare presentation of fever of unknown origin with new-onset atrial fibrillation in an otherwise healthy adult.