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68 EW CORNEA March 2012 Cornea editor's corner of the world Distinguishing dendrites by Faith A. Hayden EyeWorld Staff Writer M T he term dendrite is defined as a branching treelike figure. This term describes a shape. When clinicians see a "branching treelike figure" in the corneal epithelium, the most immediate thought is herpes simplex virus (HSV) keratitis. It is important for clinicians to realize that a dendrite (referring to the shape) is not al- ways the infectious epithelial lesion of HSV. There are many other "dendritic" lesions of the corneal epithelium that are not due to HSV and have been referred to as "pseudodendrites." It is very common to see patients with healing epithelial defects or neurotrophic epitheliopathy present with a "dendrite" or a branching epithelial lesion. These patients are often placed on topical antivirals, which leads to delayed epithelial healing and persistence of this pseudoden- drite. In addition, the label of HSV is often permanently attached to the patient. A detailed history, careful slit lamp examination, and close monitoring of the clinical course will assist the clinician in determining the correct diagnosis and treatment for these challenging patients. Clara Chan, M.D., and Mark Mannis, M.D., give us their insights for the exami- nation of the patient with a "dendrite." Edward J. Holland, M.D., cornea editor any epithelial lesions have a dendritic shape. Although most of these lesions are pseudodendrites, they are frequently misdiagnosed as her- pes simplex virus (HSV). The shape differences between these dendrites are subtle, but do exist. EyeWorld spoke to two experts on the subject who weighed in on the telltale signs. True HSV dendrites Authentic HSV epithelial disease typically presents as a unilateral, branching lesion with little end bulbs, which stain very brightly with fluorescein. "It's usually in the context of previous herpetic infections," said Mark J. Mannis, M.D., professor and chair, ophthalmology and vi- sion science department, University of California, Davis. "It can present as a keratitis. It can be very large, it can be very tiny, and therein lies the difficulty. It can present in someone who doesn't have a history of diag- nosed herpes simplex." True HSV also progresses in stages, said Clara C. Chan, M.D., professor of ophthalmology, University of Toronto. Vesicles will form and appear as small, raised lesions at first and will not stain with fluorescein. "Vesicles should not be con- fused with punctate epithelial ero- sions, which stain positively with fluorescein," Dr. Chan said. "Within approximately 24 hours, these vesi- cles coalesce to form the classic den- drite that most ophthalmologists recognize." "The virus bounces from cell to cell, so each lesion develops one cell at a time, which is why you get this linear lesion because there are cells falling out and virus cells filling in," Dr. Mannis explained. HSV, however, doesn't always present this way. For example, im- mune-compromised patients may have vesicles only and no dendrite, said Dr. Chan. On the other hand, patients with recurrent HSV keratitis and intact immune systems may have these vesicles early on in a re- currence prior to examination. If a patient has an enlarged den- drite that's not linear, it's a geo- graphic ulcer. A classic clinical observation is a scalloped-shaped boarder, not to be confused with Acanthamoeba epithelial keratitis pseudodendrite Source: Edward J. Holland, M.D. Neurotrophic epitheliopathy pseudodendrite Source: Edward J. Holland, M.D. HSV vesicles Source: Clara C. Chan, M.D. Acanthamoeba epithelial keratitis pseudodendrite Source: Edward J. Holland, M.D. healing abrasions and epithelial de- fects from neurotrophic keratopathy, which have smooth borders. "Many clinicians associate prior topical steroid use with geographic ulcers, but a geographic ulcer from HSV may form without prior topical steroid use as well," Dr. Chan said. Pinpointing pseudodendrites "The term pseudodendrite is a little bit of a misnomer," Dr. Mannis said. "We call them pseudodendrites be- cause they are not herpes simplex, but they are in fact dendrites." Varicella zoster (VZV) dendrites are quite different from HSV. For ex- ample, unlike HSV, which stains brightly, VZV stains minimally. It has a "stuck on appearance" that's elevated and presents as "convo- luted clusters," Dr. Mannis said. VZV can take on a medusa-like form, with its many branches and lack of end bulbs. Furthermore, VZV is typically found in the periphery of the cornea, Dr. Chan said. They're also more superficial and have no central ulceration. Pseudodendrites have a wide variety of causes including neurotrophic epitheliopathy, Acanthamoeba, healing epithelial defect, and recurrent erosion syndrome, Dr. Chan said. continued on page 70 HSV dendrite Source: Clara C. Chan, M.D. HSV geographic ulcer Source: Clara C. Chan, M.D.