Isolated optic neuritis with a concurrent abnormal trigeminal nucleus on imaging: case report of a rare complication of herpes zoster ophthalmicus

BACKGROUND: Herpes zoster ophthalmicus (HZO) is an inflammation related to reactivation of the latent varicella zoster virus (VZV), involving the ophthalmic branch of the trigeminal nerve. Optic neuritis (ON), a rare ocular complication following HZO, has been reported in 1.9% of HZO-affected eyes. Most previous cases occurred simultaneously with other ocular complications, especially orbital apex syndrome. Moreover, detailed magnetic resonance imaging (MRI) with diffusion weighted imaging of the optic nerve and trigeminal nucleus in HZO-related ON has been rarely reported. We report a case of postherpetic isolated ON with a concurrent abnormal trigeminal nucleus on imaging. CASE PRESENTATION: A healthy 58-year-old female presented with sudden painful visual loss in her right eye for 2 days. Four weeks before the presentation, her right eye was diagnosed with HZO, and she received intravenous acyclovir for 10 days. Ophthalmic examination revealed a visual acuity of light perception and 20/20 in the right and left eyes, respectively. A relative afferent pupillary defect was present in the right eye. Neurological examination was significant for hypoesthesia in the area of the HZO. A clinical diagnosis of HZO-related right retrobulbar ON was made, and other causes of atypical ON were excluded. MRI showed enhancement and restricted diffusion of the right-sided optic nerve with linear hyperintense T2 of the right-sided spinal trigeminal nucleus and tract (STNT) along the brainstem. She received 14 days of intravenous acyclovir and 5 days of methylprednisolone. Both were switched to an oral route for 2 months. After the completion of treatment, the visual acuity was counting fingers and 20/20 in the right eye and left eye, respectively. Stable brainstem STNT abnormalities and resolution of ON were found radiologically. CONCLUSIONS: Isolated ON is a rare ocular complication following HZO. An abnormal high signal of STNT on a T2 weighted image may be present, which may be a clue for VZV-associated complications, such as HZO-related ON, especially in cases lacking an obvious history of HZO or other concomitant ocular complications. Prompt treatment with both acyclovir and corticosteroids should be started. Restricted diffusion of the optic nerve may be a predictor for poor visual recovery.