Within the plethora of conditions in the differential diagnosis of fever and altered sensorium, PAM should be entertained. This is particularly true in light of the impact climate change has had in extending the geographic boundaries of certain emerging and re-emerging infectious diseases.[10,11] PAM was once considered a disease of the southern United States; however, recent case reports have noted that it is now found as far north as Minnesota.[9,11,12,13] Nevertheless, between 2010 and 2020, most cases (approximately 17) occurred in Texas and Florida.[9]
The cause of PAM is N fowleri, a pathogenic free-living thermophilic ameba (Figure 1). It thrives in temperatures as high as 114.4 °F (45.8 °C).[12] Other amebic genera can cause disease, such as Acanthamoeba and Balamuthia, but N fowleri, of the amoeboflagellated genus, Naegleria, is the most pathogenic for humans.[6,11] N fowleri is ubiquitous; it is found in both the fresh waters and the soils of six of the seven continents.
Figure 1.
Infection with N fowleri typically occurs as contaminated fresh water is introduced into the nose, along the nasal mucosa, through the cribriform plate, and onto the olfactory bulbs of the central nervous system. The organism's cytoxic effects then proceed to destroy nerve cells. The inflammatory response causes neuronal demyelination and lysis of erythrocytes and nerve cells. The end result is a hemorrhagic necrotizing meningoencephalitis (Figure 2).[9]
Figure 2.
Patients most commonly acquire the ameba by swimming and diving in warm freshwater lakes, hot springs, ponds, and spas.[10] Another source of infection is the use of contaminated water for religious/cultural nasal ablutions and sinus-cleansing nasal irrigations.[14] Even poorly chlorinated tap water can be unsafe if it is contaminated by the ameba. Infections and deaths related to PAM have also resulted from exposure to contaminated water from backyard water slides, artificial whitewater rafting, and water skiing.[9]
Despite the global habitat of N fowleri, PAM is rarely reported. The first case was discovered in Australia and described by Fowler and Carter in 1965.[11] Several hundred more cases have been recorded around the world, and from 1962 through 2018, 145 cases have been reported in the United States. On average, three cases of PAM are reported each year in the United States.[15]
This rarity is not the only factor that makes PAM a diagnostic challenge. The initial symptoms are fairly general in nature. As the manifestations worsen, they and the usual test results seem to point to a diagnosis of bacterial meningoencephalitis. Therefore, it is not surprising that in 75% of cases, the correct diagnosis is made at autopsy.[9] It is hypothesized that the number of N fowleri cases worldwide is grossly underestimated, owing to a lack of recognition and a dearth of laboratory resources.[15]
After a mean incubation period of 5 days (range, 3-8 days), patients with PAM may present innocuously with nausea, vomiting, headache, and fever early in the course of the disease.[9] If the patient delays seeking medical care, neurologic manifestations will develop and progress ominously similarly to a case of bacterial meningitis.
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Cite this: Paul P. Rega. 13-Year-Old Boy Unaware of His Surroundings - Medscape - Sep 14, 2023.
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