Saturday, September 17, 2016

CAP16 Abstract Highlights - Naegleria fowleri: Understanding the Clinical Presentation and Autopsy Findings of a Rare and Almost Universally Fatal Central Nervous System Infection

The 2016 annual meeting of the College of American Pathlologists (CAP16) is coming up September 25-28 in Las Vegas. In this series of posts, I'll be featuring poster abstracts of particular interest to neuropathologists.

Alexander T. Damron and colleagues at Baylor College of Medicine in Houston discuss Naegleria fowleri CNS infection in Poster #114:

Naegleria fowleri is a free-living ameba known to cause primary amebic meningoencephalitis (PAM). Moreover, PAM is an acute, fulminating, and hemorrhagic infection that occurs in healthy young children with fresh water exposure in warm climates. It is postulated that Naegleria fowleri enters through the nasal passages and crosses the cribriform plate, where it reaches the subarachnoid space and disseminates into the olfactory lobes. Visvesvara et al (2007) performed a retrospective study of all reported N fowleri infections in the United States from 1937 to 2013 and found 3 survivors in 142 reported cases. Only 27% of the 142 cases were diagnosed before patient death. We present a case of a previously healthy 14-year-old boy who presented with fever, headache, vomiting, and altered mental status 8 days after swimming in a warm freshwater lake. Cerebrospinal fluid studies showed organisms consistent with amoeba (Figure 265, C). Despite neuroprotective measures and antimicrobial medications, the patient was pronounced brain dead 9 days after admission. Autopsy revealed the cause of death to be PAM from infection with N fowleri with cerebral edema and tonsillar herniation (Figure 265, D). Microscopic examination of the central nervous system revealed amoebic organisms infiltrating the meninges and diffusely involving the brain parenchyma in a perivascular distribution (Figure 265, A and B). The most critical aspect in treating patients with PAM is early detection and prompt initiation of multiple antimicrobials and neuroprotective measures.Despite current recommendations, the high mortality rate of these infections (97%–98%) suggests that an effective treatment for PAM is not yet known.

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