Giant Cell Arteritis Presenting As Pyrexia of Unknown Origin: Diagnosis Made by Bilateral Periluminal Dark Halo Sign on Color Doppler Ultrasound.

Giant cell arteritis (GCA), a vasculitis of medium- and large-sized arteries, frequently manifests with symptoms such as headaches, soreness in the scalp, and vision abnormalities. Pyrexia is an uncommon symptom and can cause a delay in diagnosis. We describe a 76-year-old woman of Chinese ethnicity who did not exhibit the typical clinical signs of GCA but instead presented with a generalized lethargy, nausea, dizziness, and a persistent fever. Numerous tests, including autoimmune, neoplastic, and viral workups, came up negative. Pyrexia did not settle despite using broad-spectrum antibiotics. A temporal artery Doppler ultrasound was performed to assess the condition further, as inflammatory markers (erythrocyte sedimentation rate, ESR, and C-reactive protein) remained high. The ultrasound Doppler results showed bilateral halo signs that are very specific for GCA. Upon starting corticosteroid treatment, there was a rapid improvement in fever and ESR. This case underscores the importance of considering GCA as a differential diagnosis for pyrexia of unknown origin, particularly in the elderly. It highlights the utility of temporal artery ultrasound in facilitating timely diagnosis in atypical cases.