Positron Emission Tomography-Computed Tomography (PET-CT) Diagnosis of Large-Vessel Giant Cell Arteritis Presenting as Pyrexia of Unknown Origin Without Classical Cranial Features: A Case Report

Giant cell arteritis (GCA) is a systemic vasculitis affecting medium and large arteries and is classically associated with cranial manifestations such as headache, scalp tenderness, jaw claudication, and visual disturbance.However, large-vessel GCA may present with non-specific constitutional symptoms, making diagnosis difficult and delaying appropriate treatment.We report the case of a 58-year-old man with a history of hypertension, type 2 diabetes mellitus, osteoarthritis, and irritable bowel syndrome who presented with a 5-6-week history of intermittent fever, night sweats, anorexia, weight loss, mild headache, and predominantly lower-limb myalgia.Extensive investigations for infection, malignancy, and autoimmune disease were unrevealing.Microbiological investigations including blood and urine cultures, viral studies, acid-fast bacilli testing, and fungal markers were negative.Autoimmune screening, including antinuclear antibodies (ANA), antineutrophil cytoplasmic antibodies (ANCA), rheumatoid factor, and anti-cyclic citrullinated peptide antibodies (anti-CCP), was also negative.Computed tomography (CT) of the chest, abdomen, and pelvis showed no evidence of occult infection or malignancy.Despite empirical antibiotic therapy, the patient remained symptomatic with persistently elevated inflammatory markers, including an erythrocyte sedimentation rate of 136 mm/hr and C-reactive protein of 196 mg/L.As part of the evaluation for pyrexia of unknown origin, fluorodeoxyglucose positron emission tomography-computed tomography (FDG PET-CT) was performed, which demonstrated increased uptake within the bilateral femoral, vertebral, and axillary arteries, consistent with large-vessel vasculitis.Following rheumatology assessment and specialist consultation, a clinical and radiological diagnosis of large-vessel GCA was made.High-dose oral prednisolone was initiated, resulting in rapid clinical and biochemical improvement, with marked improvement in inflammatory markers.A subsequent right temporal artery biopsy demonstrated histological features in keeping with GCA.This case illustrates an atypical presentation of GCA as pyrexia of unknown origin without classic cranial or visual symptoms.Several important learning points emerge.Firstly, clinicians should maintain a high level of suspicion for large-vessel vasculitis in patients over 50 who present with persistent systemic inflammation and non-specific constitutional symptoms, specifically prolonged fever, weight loss, and myalgia, even in the absence of cranial manifestations.Secondly, the case demonstrates the diagnostic utility of FDG PET-CT in identifying large-vessel vascular inflammation when initial standard workup for infection, malignancy, and autoimmune disease is unrevealing.Thirdly, in selected patients with suspected large-vessel vasculitis, FDG PET-CT can provide an important diagnostic clue and help guide timely specialist management.