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Monday, October 31, 2011

Herpes Zoster Ophthalmicus

SIGNS AND SYMPTOMS
Herpes zoster ophthalmicus (HZO) typically presents with nondescript facial pain, fever and general malaise. About four days after onset, a vesicular skin rash appears along the distribution of the fifth cranial nerve, characteristically respecting the vertical midline. The vesicles will discharge fluid and begin to scab over after about one week. The pain is extreme during the inflammatory stage, and patients are tremendously symptomatic.

Ocular involvement may include follicular conjunctivitis, epithelial and/or interstitial keratitis, dendritic keratitis, uveitis, scleritis or episcleritis, chorioretinitis, optic neuropathy, and even neurogenic motility disorders (especially fourth cranial nerve palsy). If you see vesicles at the tip of the nose (known as Hutchinson’s Sign), there is a 75 percent likelihood of ocular sequelae.

PATHOPHYSIOLOGY
HZO occurs when the trigeminal ganglion is invaded by the herpes zoster virus, a varicella-type virus which is usually referred to as “chicken pox” in children or “shingles” in adults. The virus remains dormant in trigeminal nerve cells, and can become reactivated years later by a reduction in the immune system.

Neuronal spread of the virus occurs along the ophthalmic (1st) and less frequently the maxillary (2nd) division of the fifth cranial nerve. Vesicular eruptions occur at the terminal points of sensory innervation, causing extreme pain. Nasociliary involvement will most likely cause ocular inflammation, typically affecting the tissues of the anterior segment. Contiguous spread of the virus may lead to the involvement of other cranial nerves, resulting in optic neuropathy (cranial nerve II) or isolated cranial nerve palsies (cranial nerve III, IV or VI).

MANAGEMENT
The systemic component of this disorder is best treated with oral acyclovir, (Zovirax), 600 to 800mg five times a day for seven to 10 days, starting as soon as the condition is diagnosed. Recently, famciclovir (Famvir) 500mg p.o. t.i.d. has been shown to be as effective in treating herpes zoster ophthalmicus as acyclovir 800mg fives times per day. Timing is crucial, however, to avoid post-herpetic neuralgia. To achieve maximal benefit from oral anti-viral medications, you must start therapy within 72 hours of vesicular eruption. Otherwise, the patient is at risk for developing post-herpetic neuralgia and the beneficial effects of oral anti-viral therapy are lost. You may also wish to prescribe oral steroids to alleviate pain and associated facial edema. If so, try 40 to 60mg of prednisone daily, tapered slowly over 10 days. To treat the skin lesions, applying an antibiotic-steroid ointment, such as Pred-G, to the affected areas twice daily, may help.

Ocular management depends on the severity and tissues involved. In most cases which involve uveitis or keratitis, use cycloplegia (homatropine 5% t.id./q.i.d. or scopolamine 0.25%) b.i.d./q.i.d. After ruling out herpes simplex, it’s also possible to prescribe a topical steroid such as Vexol or Pred Forte q2-q.h. In any compromised eye, prophylaxis with a broad-spectrum antibiotic is a good idea. Finally, palliative treatment consisting simply of cool compresses, and oral analgesics in extreme cases, can be comforting. Cimetidine 400mg p.o. b.i.d may provide some additional relief from the neuralgia; why this works is not entirely understood.

CLINICAL PEARLS

People over age 70 have a much greater chance of HZO infection. Also, those who are immunocompromised due to lymphoma, AIDS, Lyme disease, etc. are at an increased risk.
Ocular involvement varies greatly and is often confusing in the early stages.
Take extreme care when differentiating this condition from herpes simplex virus (HSV), particularly when there is corneal involvement. One key consideration is that the dendritic keratitis which occurs in HZO is infiltrative, while the HSV dendrites are ulcerative.
Also keep in mind the possibility of more involved and complex ocular sequelae (chorioretinitis, optic neuropathy, cranial nerve palsies, uveitic glaucoma), and apply appropriate management strategies in these cases.
Start oral anti-viral therapy within 72 hours of vesicular eruption to possibly avoid post-herpetic neuralgia.

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