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  • Tips for Making the Tricky Acanthamoeba Keratitis Diagnosis

    Speaking at Cornea Subspecialty Day on Saturday, Jeremy D. Keenan, MD, from the University of California, San Francisco, shared 5 pearls to avoid delaying the diagnosis of—or misdiagnosing—a dangerous Acanthamoeba infection.

    1) Know the epidemiology. Acanthamoeba keratitis (AK) is quite rare, accounting for only about 5% of corneal ulcers in the United States. Contact lens wear is by far the biggest risk factor, followed by freshwater exposure. “We should always ask our patients about visiting ponds, rivers, swimming pools, and hot tubs,” said Dr. Keenan, “and pay extra attention to the signs of AK during the summer months.”

    2) Know the early signs of infection, though subtle. The first sign is epitheliopathy, often diffuse, with no stromal involvement. Next you may see pseudodendrites, which—unlike herpetic dendrites—lack an epithelial defect and terminal bulbs, and an epithelial ridge. A very specific sign of AK that does involve stromal involvement is radial perineuritis. The amoeba also presents with patchy anterior stromal infiltrates scattered throughout the cornea, typically multifocal.

    If the initial symptoms are missed, a late but clear sign is a ring infiltrate.

    3) Remember AK in your differential diagnosis. AK is frequently misdiagnosed, most commonly as herpes simplex keratitis. Be sure to keep AK in mind before starting steroids for an anterior stromal condition, as the disease may worsen with these agents.

    4) Do a confocal microscopy exam. This quick test is an excellent way to detect AK cysts, and it can be done in the office.

    5) We can never replace microbiology. According to Dr. Keenan, it is important to get a lot of tissue on a corneal scraping, not only for diagnostic testing but also for debulking and for getting rid of all the cysts on the epithelium. Use this tissue to run a smear—either Giemsa or potassium hydroxide—and a culture, which will reveal active amoebas.—Aliyah Kovner

    Financial disclosures. Dr. Keenan: None.