Pseudodendrite (Zoster Lesion): How It Differs From HSV

Pseudodendrite is a raised, branching epithelial lesion of the cornea, most often seen in herpes zoster ophthalmicus.

At first glance, it can mimic the dendritic ulcer of herpes simplex virus.

However, its morphology, staining and treatment differ in ways you can see at the slit lamp.

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What a Pseudodendrite Is

A pseudodendrite forms from swollen, heaped-up epithelial cells.

There is no true ulcer, because the epithelium stays largely intact.

As a result, the lesion sits slightly above the corneal surface.

Varicella zoster virus is the classic cause.

When Zoster Pseudodendrites Appear

Zoster epithelial disease often starts as punctate epithelial keratitis within the first days of the rash.

These spots may then coalesce into pseudodendrites.

Later, delayed mucous plaques can appear with a similar look.

Therefore, timing relative to the rash helps classify the lesion (see herpes zoster ophthalmicus).

Pseudodendrite Morphology at the Slit Lamp

The lesion looks coarse, ropy and gray.

Its branches are short, thick and irregular, sometimes described as medusa-like.

In addition, the arms taper and end without any swelling.

The True HSV Dendrite

An HSV dendrite is a genuine epithelial ulcer with a fine, branching pattern.

Its branches are delicate and divide repeatedly.

Each branch typically ends in a terminal bulb.

Swollen, virus-laden cells line the ulcer margin.

Terminal Bulbs and Branch Pattern

Terminal end bulbs are the most reliable bedside discriminator.

They reflect active viral spread at the ulcer tips.

In contrast, a pseudodendrite lacks them.

Therefore, inspect every branch tip under high magnification.

Fluorescein Staining in Pseudodendrite

Fluorescein fills the base of a true dendritic ulcer and stains it brightly.

A pseudodendrite, however, stains faintly or patchily.

Instead, the dye may pool around its raised edges.

Rose Bengal and Lissamine Green

These dyes stain devitalized and swollen epithelial cells.

For example, they highlight the margins of an HSV dendrite.

They also stain zoster pseudodendrites well, because the lesion consists of abnormal cells.

So combine dyes when the picture is unclear (see corneal staining patterns).

Corneal Sensation and Associated Signs

Both viruses can reduce corneal sensation.

However, zoster often causes a deeper and more lasting loss.

Check the forehead, lids and nose tip for vesicles or scars.

Also look for stromal infiltrates, keratic precipitates and sectoral iris atrophy (see viral anterior uveitis).

History That Shifts the Diagnosis

A recent painful dermatomal rash points strongly to zoster.

In contrast, recurrent unilateral episodes and cold sores favor HSV.

Occasionally, VZV causes epithelial disease without a rash.

Laboratory Confirmation of a Pseudodendrite

Most cases need only a clinical diagnosis.

However, PCR of an epithelial swab can separate VZV from HSV when findings are atypical.

Viral culture is slower and less sensitive.

Other Causes of Pseudodendrites

• Early epithelial Acanthamoeba keratitis
• Healing corneal abrasion with irregular epithelial ridges
• Contact lens related epitheliopathy
• Topical medication toxicity
• Tyrosinemia type II

Treating a Zoster Pseudodendrite

Oral antiviral therapy for zoster is the main treatment.

Acyclovir, valacyclovir or famciclovir started early can reduce ocular complications.

Pseudodendrites usually fade as the acute phase settles.

Some clinicians add topical ganciclovir gel, although evidence for this remains limited.

Debridement has no established role here.

Treating an HSV Dendrite

HSV epithelial keratitis responds to topical or oral antivirals.

Options include ganciclovir gel, trifluridine drops, oral acyclovir or valacyclovir.

Gentle debridement can also speed healing alongside an antiviral.

Why Steroids Need Caution

Topical steroids can enlarge an HSV dendrite into a geographic ulcer.

Therefore, avoid them in active HSV epithelial disease.

Zoster patients may still need steroids for stromal keratitis or uveitis.

Even so, confirm the diagnosis first, because a misread dendrite carries real risk.

Follow-Up in Pseudodendrite Cases

Review the patient within a few days.

Then watch for stromal keratitis, uveitis, raised pressure and neurotrophic changes.

Zoster eye disease can also recur months or years later.

Counseling the Patient

Explain that the lesion is a surface sign of viral eye disease.

First, stress completing the full oral antiviral course.

Next, warn against using leftover steroid drops.

Finally, discuss shingles vaccination after recovery.

Pitfalls to Avoid

• Do not label every branching lesion as HSV before checking the branch tips
• Never start topical steroids until you exclude an HSV dendrite
• Do not skip lissamine green when fluorescein staining looks faint
• Consider Acanthamoeba in contact lens wearers

For the latest studies, see the PubMed results for pseudodendrite.

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References

1. Liesegang TJ. Herpes zoster ophthalmicus natural history, risk factors, clinical presentation, and morbidity. Ophthalmology. 2008;115(2 Suppl):S3-S12.
2. Cobo LM, Foulks GN, Liesegang T, et al. Oral acyclovir in the treatment of acute herpes zoster ophthalmicus. Ophthalmology. 1986;93:763-770.
3. Cohen EJ, Kessler J. Persistent dilemmas in zoster eye disease. Br J Ophthalmol. 2016;100:56-61.
4. Wilhelmus KR. Antiviral treatment and other therapeutic interventions for herpes simplex virus epithelial keratitis. Cochrane Database Syst Rev. 2015;1:CD002898.
5. American Academy of Ophthalmology. Basic and Clinical Science Course, Section 8: External Disease and Cornea. San Francisco: AAO; 2023.