Clinical Reasoning: A 12-Month-Old Male Child With Staring Episodes, Ataxia, and Right-sided Weakness

Baylisascaris procyonis, or raccoon round worm, is a rare cause of eosinophilic meningoencephalitis with historically poor clinical outcomes. Symptoms of neural larval migrans begin approximately 2-4 weeks after ingestion with fatigue, nausea, fever, and lethargy, then rapidly progress to weakness, incoordination, ataxia, seizures, altered mental status, and finally coma. Only 31 other cases of central nervous system Baylisascaris neural larval migrans have been reported, with over 25% being lethal. Of the remaining cases, all but three were neurologically devastated largely due to delays in diagnosis and treatment. We present a case of an infant Baylisascaris neural larval migrans manifested as right hemiparesis, ataxia, and cortical blindness. Eosinophilia was missed at an outside hospital due to misidentification of eosinophils as monocytes on automated cell differential. Repeated testing of serum and CSF revealed marked eosinophilia consistent with eosinophilic meningoencephalitis, and serum antibody testing through the Centers of Disease Control confirmed Baylisascaris infection. Notably, this child had a remarkably positive outcome with near complete recovery of neurologic function after treatment with albendazole and steroids. While eosinophilic meningoencephalitis is rare, accounting for less than 3% of all lumbar punctures with pleocytosis, this case illustrates: A) the importance of early disease recognition and treatment to improve patient outcomes and B) the fact that automated cell differentials may misidentify eosinophils as monocytes.