Herpes Zoster Optic Neuritis
Herpes zoster optic neuritis (HZON) is a rare sequela of herpes zoster ophthalmicus (HZO), It can occur either in conjunction with HZO or, more frequently, presents as a postherpetic complication, and has been reported up to 10 weeks after HZO onset. Other diseases should be considered in the differential diagnosis, including giant cell arteritis. There is no constant laboratory or imaging finding in HZON. Different treatments have been recommended for isolated HZON, from oral antivirals to IV acyclovir 10mg/kg 7-10 days. If there are other associated neurologic symptoms or other involvement on MRI brain, then acyclovir 10-15mg/kg every 8 hours for 2-3 weeks is indicated.
Herpes Zoster Optic Neuritis
Herpes zoster optic neuritis (HZON) is a rare sequela of herpes zoster ophthalmicus(HZO), or herpes zoster in the distribution of the ophthalmic branch of the trigeminalnerve. It can occur either in conjunction with HZO or, more frequently, presents as a postherpetic complication, with cases reported up to 10 weeks after HZO onset.
The pathophysiology of how VZV damages the optic nerve is uncertain. There are three proposed pathophysiologic mechanisms of HZON.
- Direct nerve infection through the cavernous sinus
- Inflammatory demyelination
- Systemic or CNS infection with reactive immune response leading to edema of the optic disc
HZO should be treated with oral antiviral therapy (acyclovir, valacyclovir, or famciclovir) plus topical steroid drops if immunocompetent or IV acyclovir (10 mg/kg three times daily for seven days) if immunocompromised. Although this may not prevent HZON, it may reduce the incidence of it.
The diagnosis of HZON should be suspected when an acute, unilateral or bilateral, anterior or retro-bulbar, optic neuropathy occurs in the setting of HZO or within about 3 months of its onset. Other disease processes should be considered as well, as discussed in the differential diagnosis section.
Symptoms of HZO (fever, malaise, eye pain, headache prior to eruption of rash in distribution of the ophthalmic branch of the trigeminal nerve) or has a previous diagnosis of HZO and presents with vision loss.
- Visual acuity is decreased in the affected eye
- Relative afferent pupillary defect in the affected eye
- Fundus exam can initially show a normal or edematous optic nerve that may progress to optic nerve atrophy
- Neurological exam can reveal hypoesthesia in the area supplied by the ophthalmic branch of the trigeminal nerve on the affected side
- MRI of orbit can show enhancement and restricted diffusion of the affected optic nerve
- T2 weighted MRI can also show linear hyperintense lesions in trigeminal nucleus of a patient with herpes zoster optic neuritis
- Fluorescein angiography can show late staining of affected optic disc
- Doppler studies of central retinal artery, posterior ciliary artery, and ophthalmic artery of affected eye are usually normal
- Consider lumbar puncture with CSF analysis to include sending paired samples of serum and CSF or intraocular fluid (in patients with uveitis) to the lab for PCR and serology, although case reports have shown negative PCR results in some suspected cases of HZON
- Other causes of optic neuropathy should be excluded by patient history and examination, including giant cell arteritis. Considerthe following tests:
- Complete blood count (CBC), erythrocyte sedimentation rate (ESR), c-reactive protein (CRP), Treponema pallidum hemagglutination (TPHA), Venereal Disease Research Lab (VDRL), antinuclear antibody (ANA), and aquaporin-4 antibody, Myelin oligodendrocyte glycoprotein (MOG)
Differential Diagnosis of Acute Optic Neuropathy:
Optic neuritis, Non-Arteritic Ischemic Optic Neuropathy, Posterior Ischemic Optic Neuropathy, Arteritic Ischemic Optic Neuropathy (Giant Cell Arteritis), Central Retinal Artery Occlusion, Toxic (should be symmetric vision loss), Infiltrative, Leber’s Hereditary Optic Neuropathy
Different treatments have been recommended for isolated HZON, from oral antivirals to IV acyclovir 10mg/kg 7-10 days. Adjunct oral corticosteroid is controversial, with some treatment recommendations consisting of oral prednisone 60 mg per day with a topical steroid if ocular inflammation is present, while others recommend avoiding adjunct oral prednisone because of lack of evidence for definitive benefit and possible risk of VZV retinitis. If there are associated neurologic symptoms or other involvement on MRI brain, then acyclovir 10-15mg/kg every 8 hours for 2-3 weeks is indicated.
Visual recovery is variable. Poor visual prognosis is usually seen in patients with concomitant ocular complications of HZO. Restricted diffusion of the optic nerve on MRI has been proposed as a predictor for poor visual recovery.
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