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31 August 2011 Case of the Week #215
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Case of the Week #215
A 2 year old boy from El Paso was in good health until he began experiencing mild rhinorrhea and cough, followed by acute onset of left sided weakness. Lumbar puncture revealed a pleocytosis of 111 WBC. MRI revealed diffuse contrast-enhancing lesions with surrounding edema throughout the bilateral cortex, midbrain, pons and cerebellum, thought to be consistent with cysticerci. The patient was managed with albendazole therapy and intravenous steroids, and improved sufficiently to be discharged home. A week later, he worsened again and presented with hemiparesis, ataxia and inability to handle secretions. By MRI, the lesions had increased in size. Pertinent history includes regular travel to Mexico, but no known sick contacts at home and no known TB in the family. A biopsy was performed.
What is your diagnosis?
Balamuthia mandrillaris encephalitis
The diagnosis was confirmed by PCR performed by the US Centers for Disease Control.
Balamuthia mandrilaris is an amoeba that primarily affects the nasal pyramid or the skin, producing granulomatous amoebic lesions (Hum Pathol 1999;30:269). The amoebae spread from the primary nasal lesion to the meninges, where they infiltrate vessels. Thrombotic amoebic angitis produces CNS infarcts, that are infiltrated by amoebae.
Balamuthia infection is extremely rare, with fewer than 200 human cases recognized worldwide since it was found to be a human pathogen in 1990. Balamuthia is often misdiagnosed as other neurologic diseases (Clin Infect Dis 2009;48:879). Infection occurs in both immunocompromised and otherwise healthy persons, and often in children. Risk factors are poorly defined, but might include exposure to soil or stagnant water, young age and Hispanic ethnicity. Balamuthia can also be transmitted by organ transplant (MMWR Morb Mortal Wkly Rep 2010;59:1165).
Clinically, patients can have skin lesions months to years before having encephalitis symptoms. At biopsy, an amoebic trophozoite is observed, often infiltrating vessels. The amoebae have a nucleus with a large, central karyosome and vacuolated cytoplasm.
Cysts and trophozoites
Once infection progresses to encephalitis, it is almost always fatal, although a few patients have survived (Clin Infect Dis 2010;51:e7, Pediatrics 2010;125:e699)
Differential diagnosis includes other amoebae that attack the CNS, including Acanthamoeba, Naegleria fowleri and Sappinia, which have microscopic differences in the cysts and trophozoites (Centers for Disease Control). In this case, the two year old boy died of his disease, and no autopsy was performed.
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and Liz Parker, B.A., Associate Medical Editor
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