Granulomatosis With Polyangiitis Mimicking Giant Cell Arteritis.

Granulomatosis with polyangiitis (GPA) is a rare auto-immune ANCA-associated small-vessel vasculitis characterized by necrotizing granulomatous inflammation, primarily affecting the sinuses, respiratory tract, and kidneys. Early diagnosis and treatment are crucial for improving patient outcomes and preventing rapidly progressive renal failure. We present a case of a 66-year-old woman presenting to the emergency department (ED) with a two-week history of productive cough, nausea, fevers, and headache. Observations and routine blood tests were unremarkable, so the patient was treated with antibiotics for a chest infection. Headache became a particularly prominent feature, along with jaw claudication and temporal tenderness. Treatment for another vasculitis, giant cell arteritis (GCA), was started and then stopped after ultrasound scanning showed no signs of GCA. After repeated admissions to the hospital, she was eventually diagnosed with GPA after the auto-immune screening was sent, which was positive for cANCA (anti-PR3). This case highlights a high degree of diagnostic uncertainty due to multiple investigations revealing the involvement of different organs, but these were treated separately. A more holistic approach to multi-system pathology, as well as considering other causes of fever and raised inflammatory markers, would have spared the patient from many unnecessary and invasive investigations. The patient eventually made a rapid recovery after the initiation of appropriate immunosuppressant therapy.