Etiology: Caused by cystic larval stage of Taenia solium, the pork tapeworm. Humans become infected with the tapeworm form by ingesting undercooked pork infected with cysticerci; eggs and proglottids are shed in the feces. Pigs then become infected by ingesting these eggs from human feces, which hatch and migrate into tissues, and eventually mature into cysticerci. Human cysticercosis results from ingestion of ova shed by a human tapeworm carrier; close personal contact or food preparation by a tapeworm carrier is usually noted, and autoinfection can even occur.

Epidemiology: It is estimated that up to 50% of Latin American patients with new-onset seizures have CT scan evidence of neurocysticercosis. In India, up to 40% of patients presenting with localizing seizures were found to have calcifications or enhancing lesions consistent with cysticercosis. In endemic villages in Central and South America, seroprevalence rates have been reported from 5-25%. In the U.S., neurocysticercosis is primarily an imported disease with an estimated 1000 new cases each year; most cases occur among Latin American immigrants.

Pathogenesis: The viable cysticercus is a thin-walled, oval cyst ~ 1cm in diameter. Initially, there is minimal associated inflammation and patients are usually asymptomatic unless the growing cyst exerts a significant mass effect; . The cyst eventually loses its ability to control the host response and the cyst becomes infiltrated with mononuclear inflammatory cells, forming a degenerating cyst as it collapses; such cysts are usually the ones responsible for symptoms. Eventually the cysts fibrose and calcify.

Clinical Presentation: Most common manifestation is seizures(either focal or generalized); seizures are usually associated with degenerating cysts with surrounding inflammation. Patients with seizures who have inactive calcific neurocysticercosis may also present with seizures but frequently have negative EEGs. Such patients will usually require continuous anticonvulsant therapy for "unprovoked" seizures. Headaches are also common, especially when associated with ventricular or cisternal lesions. Patients can also manifest signs of increased intracranial pressure, usually due to obstruction of CSF flow in the ventricles or cisterns. Visual changes or even blindness can occur in patients with ocular/retinal involvement. Morbidity in neurocysticercosis is generally related to inflammatory reactions to the active cysts.

Diagnosis: Classic lesion on CT or MRI scanning is a cystic lesion with surrounding enhancement associated with a 1-3mm mural nodule; CT is generally more sensitive than MRI for detection of calcified lesions. Serum enzyme-linked immunotransfer blot (EITB) is highly specific but has poor sensitivity, particularly in patients with calcified lesions from prior infection. CSF antigen detection is specific but not sensitive. Proposed "major" criteria for the diagnosis of neurocysticercosis include 1) CT or MRI consistent with neurocysticercosis (cystic lesions or calcifications), 2) positive EITB, or 3) typical muscular calcifications. Proposed "minor" criteria include consistent symptoms, punctate calcifications, disappearance of lesions with treatment, or subcutaneous nodules; patients should have an exposure risk to a tapeworm carrier or travel to an endemic area. 2 major or 1 major + 2 minor and exposure considered diagnostic.

Treatment: For inactive disease, treat symptoms only - i.e. treat seizures with anticonvulsant therapy, VP shunting +/- corticosteroids for patients with hydrocephalus, etc.

For active disease, praziquantel 50-100mg/kg/day in 3 divided doses for 14 days or albendazole 15mg/kg/day in 2 divided doses for 7 days. Unclear whether these drugs offer significant benefit over symptomatic therapy alone.

D. Suh 2/27/01