Clinical Features:
Acute primary amebic meningoencephalitis (PAM) is caused by Naegleria fowleri.  It presents with severe headache and other meningeal signs, fever, vomiting, and focal neurologic deficits, and progresses rapidly (<10 days) and frequently to coma and death.  Acanthamoeba spp. causes mostly subacute or chronic granulomatous amebic encephalitis (GAE), with a clinical picture of headaches, altered mental status, and focal neurologic deficit, which progresses over several weeks to death.  In addition, Acanthamoeba spp. can cause granulomatous skin lesions and, more seriously, keratitis and corneal ulcers following corneal trauma or in association with contact lenses.

Laboratory Diagnosis:
In Naegleria infections, the diagnosis can be made by microscopic examination of cerebrospinal fluid (CSF).  A wet mount may detect motile trophozoites, and a Giemsa stained smear will show trophozoites with typical morphology.  In Acanthamoeba infections, the diagnosis can be made from microscopic examination of stained smears of biopsy specimens (brain tissue, skin, cornea) or of corneal scrapings, which may detect trophozoites and cysts.  Cultivation of the causal organism, and its identification by direct immunofluorescent antibody, may also prove useful.

Diagnostic findings

• Microscopy

Treatment:
Eye and skin infections caused by Acanthamoeba spp. are generally treatable.  Topical use of 0.1% propamidine isethionate (Brolene) plus neomycin-polymyxin B-gramicidin ophthalmic solution has been a successful approach; keratoplasty is often necessary in severe infections.  Although most cases of brain (CNS) infection with Acanthamoeba have resulted in death, patients have recovered from the infection with proper treatment.  Amphotericin B* has been successfully used to treat PAM caused by Naegleria fowleri.  See recommendations in The Medical Letter for complete information.

*This drug is approved by the FDA but considered investigational for this purpose.