Optic neuritis secondary to herpes zoster ophthalmicus

INTRODUCTION

Varicella zoster virus infection commonly affects children and is spread by airborne, droplet, and contact transmission. Herpes zoster occurs as a result of reactivation of the latent varicella-zoster virus residing in the sensory nerve ganglion and presents at a later stage of life. It usually presents with an unilateral maculopapular or vesicular rash confined to a dermatome-Hutchinson’s sign. Herpes zoster ophthalmicus (HZO) occurs when there is involvement of the ophthalmic division (V1) of the trigeminal nerve.^[1] Ocular manifestations can include conjunctivitis, anterior and posterior uveitis, episcleritis, keratitis, and retinitis. Neuroophthalmic complications are rare and include third cranial nerve palsy, optic neuritis (ON), and orbital apex syndrome. Central nervous system manifestations include cranial nerve palsies, meningitis, and encephalitis.

CASE REPORT

A 19-year-old female with no known comorbidities presented to Sri Ramachandra Hospital with an acute onset of pain in the right eye for 4 days and inability to open the right eye for 1 day. She was apparently asymptomatic 4 days ago and then developed sudden onset pain in the right eye with multiple painful fluid-filled vesicles around the right eye and the right side of the nose and forehead. A history of fever and photophobia was present. The patient had a history of chicken pox at the age of 12 years. On initial examination, visual acuity in the right eye was limited to finger counting, and the left eye was 6/6. Local examination of the left eye was normal while the right eye revealed inability to open eyelid, lid edema, and unilateral right-sided crusty lesions till the tip of the nose. Detailed initial ophthalmic examination of the right eye revealed anterior segment congestion, flare and occasional cells in anterior chamber, sluggishly reacting pupil (relative afferent pupillary defect [RAPD] present), clear lens, cornea showed deposits on endothelium taking up stain, keratic precipitates and multiple dendritic lesions with stromal keratitis and fundus examination could not be done initially. Basic investigations done showed a normal complete blood picture, renal and liver function tests, and non-reactive viral markers, and a normal chest X-ray as mentioned in Table 1.

The patient was started on tablet valacyclovir 1 g thrice daily and topical steroid eye drops. After 1 week, when the patient was able to open eyelids and noticed diminished vision - only hand movements/counting fingers close to face, cornea clear-resolved keratitis, pupil sluggishly reacting, and was not able to see the floor. On examination, right inferior quadrantanopia was noted. Repeat fundus examination showed temporal disc pallor, while the macula and periphery were normal. ON secondary to HZO was considered. Magnetic resonance imaging (MRI) of the brain with orbital cuts done revealed intraconal, intracanalicular part of right optic nerve sheath complex thickening with surrounding fat stranding and homogenous enhancement on post-contrast administration, features likely representing ON secondary to HZO [Figure 1]. Visually evoked potential done showed a delayed p100 response. Perimetry showed right inferior and temporal field deficits. IV methylprednisolone 1 g once daily for 5 days was started and injection acyclovir was given for 7 days, and the patient showed gradual improvement in vision to 6/24, cornea clear, eye quiet, RAPD, and temporal pallor present.

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Figure 1:

Magnetic resonance imaging (MRI) brain contrast with orbital cuts of a 19 year-old female with acute onset of pain in the right eye (a) Axial section showing intra conal ,intra canalicular part of right optic nerve sheath complex thickening with fat stranding and homogenous enhancement (blue arrow). (b) Coronal section showing the same findings as mentioned above (blue arrow).

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DISCUSSION

HZO resulting in ON is a rare complication and has been reported in only 1.9% patients.^[2] Risk factors include older age, immune immune-compromised state like human immunodeficiency virus, lymphoma, leukemia, if on immunosuppressive therapy, and diabetes mellitus. In general, ON manifests between 6 and 30 days from the onset of vesicular rash.^[3] Herpes zoster ON can have either an anterior or retrobulbar form. The exact pathogenesis remains elusive; however, proposed mechanisms include that (I) the virus may spread through cavernous sinus and superior orbital fissure to the orbit causing optic nerve injury, (II) local extension into meninges, brain tissue can lead to meningoencephalitis and damage optic nerve, and (III) it can be as a result of generalized ocular ischemia caused by inflammation of posterior ciliary arteries and nerves.^[4]

Unilateral involvement is more common than bilateral involvement. MRI findings include enhancement and restricted diffusion of the affected optic nerve. T2-weighted MRI can show linear hyperintense lesions in the trigeminal nucleus. Treatment may include oral to IV acyclovir 10 mg/kg for 7–10 days. Adjunct oral steroids are controversial with some recommendations suggesting oral prednisone 60 mg/day with a topical application if ocular inflammation is present while some suggest avoiding adjunct oral steroids because of the possible risk of retinitis.^[2] If there are other neurological symptoms or involvement on imaging, acyclovir 10–15/kg every 8 h for 2–3 weeks is advised. In our case, the patient had a drastic improvement once started on systemic steroids along with antivirals. Hence, treatment has to be tailored according to the patient’s presentation as it is variable.

Visual recovery is usually noted around 4 weeks. Poor prognosis has been seen in those associated with other ocular complications. Prompt treatment is crucial for better outcomes, or else, the patient can land up with optic nerve atrophy.

CONCLUSION

Patients with HZO should be under high vigilance for any visual field-related symptoms since ON is a vision-threatening condition. Early identification and prompt treatment with antivirals± steroids is crucial. Vaccination is advised for at-risk individuals.