Acute retinal necrosis associated with dimethyl fumarate

<h3></h3> A 44-year-old man with relapsing-remitting multiple sclerosis (MS) on dimethyl fumarate (DMF) presented with acute left-sided eye pain and visual impairment (47 letters). Indirect fundoscopy revealed panuveitis with arteritis, venulitis and multifocal areas of retinitis consistent with acute retinal necrosis (ARN). Peripheral blood lymphocyte count was normal. Vitreous PCR was positive for varicella zoster virus (VZV). DMF was discontinued and treatment initiated with cyclopentolate, prednisolone eye drops, valaciclovir and intravitreal foscarnet. Oral prednisolone (60mg) was introduced at 48 hours. At 6 weeks, left-sided acuity was 77 letters, and intraocular inflammation had resolved. ARN (1/1.6-2 million/year) is a sight-threatening pan-uveitis associated with herpesvirus infection, usually VZV. Prompt treatment reduces the risk of intraocular complications and risk to the contralateral eye. Age and immunosuppression are risk factors and are associated with reduced VZV- specific T-cell-mediated immunity. DMF depletes T cells (particularly CD8+) and 4 cases of severe herpes zoster have been reported. We are not aware of a previous report of ARN in association with DMF. This case highlights the importance of post-marketing drug surveillance and considering causes other than optic neuritis for reduced visual acuity in MS. The presence of vasculitis, retinitis and vitritis should prompt consideration of an infective aetiology.