Bilateral optic perineuritis as the presenting feature of giant cell arteritis.

Optic perineuritis (OPN) is an uncommon inflammatory disorder of the optic nerve sheath. Most cases are idiopathic, though OPN can rarely occur as a manifestation of vasculitic diseases. We describe the case of a 74-year-old Caucasian man presenting with diplopia and bilateral visual loss. A brain MRI showed bilateral OPN without involvement of other structures. All the tests performed to investigate OPN's aetiology showed negative results. Considering clinical presentation and neuroimaging findings, a diagnosis of bilateral idiopathic OPN was made. Treatment with intravenous high-dose steroid was administered. Four weeks after admission, the steroid therapy was interrupted because of Listeria monocytogenes invasive infection. After steroid treatment withdrawal, the patient developed jaw claudication and bilateral skin necrosis of the temporal region, clinical features that are highly specific for giant cell arteritis (GCA). On this basis, a diagnosis of bilateral OPN secondary to GCA was made.