Mydriatic pupil in giant cell arteritis.

A mydriatic pupil has been infrequently reported as a manifestation of giant cell arteritis. We report a patient with acute, evolving pupil dilation who was diagnosed with biopsy-proven giant cell arteritis. We document the time course for the development of pupillary near-light dissociation and denervation hypersensitivity. We discuss the possible mechanisms leading to mydriasis, including 1) parasympathetic dysfunction due to ischemia of the ciliary ganglion and post-ganglionic parasympathetic fibers and 2) direct iris ischemia. Repeated episodes of pupil dilation in this patient suggested ongoing microvascular insufficiency.