December 2014

An 85-year-old woman with right eye pain

Majed Pharaon M.D., Kymberly Gyure M.D.

Clinical History

An 85 year-old woman with a past medical history of trigeminal neuralgia, glaucoma, and hypothyroidism presented with right eye pain and a sudden decrease in vision. Ophthalmic examination revealed right corneal ulceration and edema. Routine cultures of the right eye and PCR were performed. Antibiotics and antivirals were prescribed with no response. A right keratoplasty was performed.

Microscopic Description

Sections of the cornea (hematoxylin-eosin and PAS) showed the findings illustrated in figures 1 and 2.

image1.jpg
Figure 1 (hematoxylin-eosin, original magnification 400x)
image2.jpg
Figure 2: (PAS, original magnification 400x)

Diagnosis

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Discussion

Acanthamoeba spp. are free-living amebae and are among the most common protozoa found in the environment. They have a worldwide distribution [1] and are the causative agents of granulomatous amebic encephalitis and amebic keratitis [2]. They can be found in soil, dust, air, natural and treated water, sea water, and swimming pools. Poor contact lens hygiene is the main risk factor for the development of amebic keratitis, especially in developed countries [3]. Immunocompromised individuals such as AIDS patients are at increased risk for developing disseminated amebic infections [1].
Clinical manifestations of amebic keratitis include eye pain, hyperemia, foreign body sensation, photophobia, and decreased vision. A history of minor trauma to the eye can be reported and is usually caused by contact lenses. On ophthalmoscopic examination, early findings such as corneal opacity and ulceration can be mistaken for Herpes simplex keratitis [4]. Ring-shaped stromal infiltrates are considered characteristic but late findings in amebic keratitis [5].
Diagnosis of Acanthamoeba is made based on the combination of clinical manifestations and laboratory findings. Bacterial, viral, or fungal organisms are more frequently associated with keratitis. This fact can delay the accurate diagnosis of amebic keratitis; affecting the prognosis of the disease. A quick method to detect trophozites is by staining corneal scrapings with a chemo-fluorescent dye such as calcofluor white. This dye is not very specific because it can detect other fungal elements [6]. Real-time PCR is the most sensitive method for detecting amoeba-derived DNA [4,7,8]. Another method of detecting the organism is by visualization of amebic cysts or trophozites using light microscopy, as in the present case. Histologic sections typically show small cysts with a varying degree of adjacent inflammation. Special stains such as Periodic acid-Schiff (PAS) can be helpful. The patient presented in this case was diagnosed with a non-specific keratitis initially and was started on anti-bacterial and anti-viral agents, to which she did show significant response. Her bacterial and viral cultures were negative. PCR for Acanthamoeba was performed and was positive.
Treatment of amebic keratitis can be lengthy due to difficulty in diagnosis or a multi-resistant strain. Current treatment options include the use of antiamebic agents such as polyhexamethylene biguanide (PHMB) and chlorhexidine either as a monotherapy or in combination [9]. The disease usually responds within one week, especially if the patient presents in the first eight weeks of onset. Patients presenting after three or more months of onset may require prolonged drug therapy in addition to surgical debridement and grafting. Steroids may be warranted in advanced cases. 

References

  1. Marciano-Cabral, F., and Cabral, G (2003). Acanthamoeba spp. as agents of disease in humans. Clin Micro Rev 16(2):273-307.
  2. Martinez, A. J., and G. S. Visvesvara (1997). Free-living, amphizoic and opportunistic amoebas. Brain Pathol 7:583–598.
  3. Mannis MJ, Tamaru R, Roth AM, et al (1986). Acanthamoeba sclerokeratitis. Determining diagnostic criteria. Arch Ophthalmol 104:1313-1317.
  4. Ikeda Y, Miyazaki D, Yakura K, et al (2012). Assessment of real-time polymerase chain reaction detection of Acanthamoeba and prognosis determinants of Acanthamoeba keratitis. Ophthalmology 119:1111-1119.
  5. Schuster FL, Visvesvara GS (2004). Free-living amoebae as opportunistic and non-opportunistic pathogens of humans and animals. Int J Parasitol 34:1001-1027.
  6. Wilhelmus KR, Osato MS, Font RL, et al (1986). Rapid diagnosis of Acanthamoeba keratitis using calcofluor white. Arch Ophthalmol 104:1309-1312.
  7. Seal DV (2003). Acanthamoeba keratitis update-incidence, molecular epidemiology and new drugs for treatment. Eye (Lond) 17:893-905.
  8. Khan NA, Jarroll EL, Paget TA (2001). Acanthamoeba can be differentiated by the polymerase chain reaction and simple plating assays. Curr Microbiol 43(3):204-208.
  9. Lim N, Goh D, Bunce C, et al (2008). Comparison of polyhexamethylene biguanide and chlorhexidine as monotherapy agents in the treatment of Acanthamoeba keratitis. Am J Ophthalmol 145:130-135.