Review Question - QID 215135

The patient has evidence of primary amebic meningoencephalitis as suggested by the fulminant course of intracranial infection (1 day to fever and altered mental status), swimming in freshwater sources, meningeal signs (Brudzinski sign: reflex flexion of hips and/or knees on neck flexion), and cerebrospinal fluid findings (leukocytosis with neutrophilia, presence of RBCs, low glucose, elevated protein, and absence of bacteria). Primary amebic meningoencephalitis is caused by Naegleria fowleri.

Primary amebic meningoencephalitis is a deadly disease caused by the thermophilic protozoan, N. fowleri. The trophozoite enters the host through the cribriform plate. Hence, one of the greatest risk factors is water sports, though infection has been documented through nasal irrigation and use of contact solution. The infection occurs rapidly and often presents with high fever, nausea, vomiting, neurological (e.g., headache, photophobia, altered mental status, and seizures) and meningeal signs. CSF findings are similar to those seen in bacterial meningitis, but there is usually no evidence of bacteria. Diagnosis is established by observation of motile trophozoites on CSF wet mount preparation. Although optimal management of primary amebic meningoencephalitis is unclear, the few documented survivors were all diagnosed early and received prompt amphotericin B.

Incorrect Answers:
Answer 1: Herpes simplex virus type 1 (HSV-1) is a common infection that is spread via oral secretions. After the initial infection, it chronically infects the neural ganglia and can reactivate in times of stress. Although presentation is often just limited to cold sores, HSV-1 can also cause encephalitis. HSV encephalitis would present with a fever, altered mental status, and possible seizures and olfactory hallucinations. Lumbar puncture would demonstrate an elevated cell count (predominantly lymphocytes), an elevated protein, a normal glucose, and an elevated red blood cell count with xanthochromia.

Answer 3: Neisseria meningitidis is a leading cause of bacterial meningitis in young adults. Symptoms include fever, nausea, vomiting, petechial rash, and shock. The CSF profile in N. meningitidis infection is very similar to that seen in primary amebic meningoencephalitis, but the Gram stain would identify gram-negative diplococci.

Answer 4: Trypanosoma brucei causes trypanosomiasis, also known as sleeping sickness. It initially presents with fevers, malaise, and intermittent headaches, but eventually progresses to meningoencephalitis. In addition, a red chancre usually forms 1 week after the infected tsetse fly bite. The acute form of infection can progress in a few weeks while the chronic form can take years. Its CSF profile would appear similar to primary amebic meningoencephalitis. However, given the patient’s fulminant presentation and lack of insect bite, it is a less likely cause.

Answer 5: West Nile virus infection is a common arbovirus transmitted by the Culex mosquito. For most patients, they only develop a self-limited fever with malaise, myalgias, and anorexia along with a maculopapular rash. In severe neuro-invasive disease, meningitis, encephalitis, and/or flaccid paralysis can be seen. The CSF would have a viral profile (normal pressure, normal glucose, presence of monocytes, and normal protein).

Bullet Summary:
Exposure to freshwater with fulminant development of meningeal (reflex flexion of hips and/or knees on neck flexion) and neurological signs (headache, photophobia, altered mental status, and seizures) should prompt consideration of Naegleria fowleri meningoencephalitis.