If a patient whom you suspect has herpes simplex virus (HSV) doesnt respond to treatment, consider instead a diagnosis of Acanthamoeba keratitis (AK), according to a study in the July issue of Cornea.

The retrospective review, performed at Wills Eye Hospital in Philadelphia, analyzed all cases of AK that had presented between January 1995 and December 2005. The study was intended to analyze the increase in cases in this time frame, as well as any common risk factors, treatment strategies and outcomes.

Not only did the incidence of AK diagnosis increase between 1995 to 2003 (11 patients) and 2004 to 2005 (20 patients), but 70% of the patients diagnosed after 2004 (14 out of 20) were originally misdiagnosed with HSV.

Often, early in Acanthamoeba infections, there is a dendritic epithelial pattern, which can be mistaken as HSV, says Christopher J. Rapuano, M.D., of Wills Eye Hospital, one of the studys authors. But, the dendritic pattern in Acanthamoeba is typically not ulcerated, doesnt have classic branching lines, and doesnt have terminal end-bulbs. And, it is much, much more painful than HSV.

These 14 patients had been receiving antiviral treatment instead of the appropriate antiamoebic agents. Such misdiagnoses, which delayed treatment for Acanthamoeba, could potentially worsen the patients visual prognosis due to this delay and possible toxicity. Look very closely at the dendrite, Dr. Rapuano says. If there is history of contact lens use, if there is significant pain, and if the dendrite is not classic for HSV, consider Acanthamoeba.

The study also found that 19 of the 20 patients (95%) had been misdiagnosed with bacterial keratitis and were treated with antibiotics during the course of therapy, and that 14 (70%) had been managed with topical steroids.

The antibiotic treatment probably didnt help or hurt, except for possible toxicity, says Dr. Rapuano. But, the steroids may have made the Acanthamoeba worse.

Make certain not to misdiagnose AK, the authors warn: Consider AK in any patients with a history of contact lens wear who are unresponsive to treatment of HSV.


Thebpatiphat N, Hammersmith KM, Rocha FN, et al. Acanthamoeba keratitis: a parasite on the rise. Cornea 2007 Jul;26(6):701-6.

Vol. No: 144:08Issue: 8/15/2007