The mirrored arterial dilemma.

An 89-year-old man presented with acute and painless loss of vision in his left eye. He denied constitutional symptoms. Visual acuity was light perception with pallid optic disc edema. Neurological work-up and serological inflammatory markers were normal. Due to the clinical suspicion for giant cell arteritis (GCA), he was started on corticosteroid therapy and bilateral temporal artery biopsies (TABs) were performed. Histopathology of the left temporal artery ipsilateral to the visual loss was negative for arteritis, while the contralateral temporal artery was positive for arteritis. The diagnostic evaluation of GCA and value of unilateral versus bilateral TABs is discussed.