Granulomatosis with polyangiitis manifesting as fever of unknown origin.

Fever of unknown origin (FUO) has a broad differential diagnosis, including infectious, inflammatory and malignant aetiologies. Granulomatosis with polyangiitis (GPA) can present with non-specific symptoms, including fever, lethargy and flu-like illness. While systemic vasculitis causing FUO has been well-documented, GPA as an underlying cause for FUO poses a diagnostic and therapeutic challenge for clinicians. We present the case of a 65-year-old man who presented to the emergency department with a report of fever, myalgia and night sweats for greater than 3 weeks. After an extensive workup, the patient was diagnosed with GPA and he eventually responded to corticosteroids and immunosuppressive therapy. This case aims to raise awareness of FUO secondary to GPA and serves as a reminder to clinicians that early recognition and prompt treatment of this syndrome improves patient outcomes.