eMedicine Specialties > Pediatrics: General Medicine > Parasitology

Neurocysticercosis

Author: Vinod K Dhawan, MD, FACP, FRCP(C), Professor, Department of Clinical Medicine, University of California at Los Angeles; Professor of Medicine, Charles R Drew University of Medicine and Science; Chief, Division of Infectious Diseases, MLK-Harbor Hospital
Coauthor(s): Eric HW Kossoff, MD, Assistant Professor, Departments of Pediatrics and Neurology, Associate Director of Pediatric Neurology Residency Program, Johns Hopkins School of Medicine
Contributor Information and Disclosures

Updated: Sep 12, 2007

Introduction

Background

Neurocysticercosis is the most common parasitic infection of the CNS. Tissue-invading larval forms of the pork tapeworm Taenia solium cause the disease. Historically, neurocysticercosis was endemic to only Latin America, Asia, and Africa, although it has become increasingly frequent in the United States since the 1980s. Because of this epidemiologic change, all general pediatricians should become familiar with this disease process.

Pathophysiology

The larvae of T solium (Cysticercus cellulosae) cause neurocysticercosis. This pork tapeworm can vary in size but is notable for a scolex (head) with approximately 25 hooklets, 4 suckers, and a body with 700-1000 proglottids. The ova of the tapeworm are spread via the fecal-oral route and are approximately 40 microns in diameter with a radially striated shell. The intermediate host is the pig, which harbors the larvae after eating ova, while the definitive host is the human being.

If pig products infected with larvae are ingested, a tapeworm infection in the intestines ensues; however, if ova are ingested, neurocysticercosis may occur in this normally intermediate host. The ingested ova develop into larvae (cysticerci) and lodge in soft tissues, especially skin, muscle, and brain. Cysticerci are fluid-filled oval cysts, approximately 1-2 cm in diameter, with an internal scolex.

The eggs are found in human feces because humans are the only definitive hosts. Greatest risk for infection occurs in regions where plants in gardens or farms are fertilized with human feces and humans are exposed to contaminated soil.

In the CNS, T solium is deposited in the cerebral parenchyma, meninges, spinal cord, and eyes. Unless large numbers of cysts are present, the body's immune system does not act to destroy the organism, and cysts can live for many years undetected. A live cyst can go undetected for as long as 5 years before dying or causing symptoms in the host.

Neurologic symptoms arise when the encysted worm dies and the human mounts an associated inflammatory response. If the cyst lodges in the ventricular system (especially the fourth ventricle), hydrocephalus can occur.

Frequency

United States

Neurocysticercosis is more common among immigrants from endemic areas or children in contact with these immigrants. Several studies report approximately 1000 cases annually in adults and children. One study reported neurocysticercosis as the cause of 2% of the neurologic and neurosurgical admissions in southern California.¹ With increasing immigration from Mexico and other endemic areas, incidence in the southern United States has been increasing. In a recent meta-analysis of the US medical literature, 1494 cases have been reported from 1980-2004.²

International

Neurocysticercosis is highly endemic in Latin America, Mexico, Eastern Europe, Asia, Africa, and Spain. The estimated serologic prevalence in Mexican adults is 3.6%, with positive confirmation by autopsy in 1.9%. Approximately 50 million people worldwide are infected.

Mortality/Morbidity

• Neurocysticercosis is typically benign, and most lesions spontaneously resolve within 2-3 months; however, mortality is highly dependent on whether the disease process is simple or complicated.
• Simple neurocysticercosis occurs in children with only a single exposure to cysts. These children tend to have solitary cysts and fewer complications. Often, children can be treated symptomatically and have a favorable prognosis. This type of neurocysticercosis tends to be observed in the United States and other nonendemic areas.
• Complicated neurocysticercosis occurs in children in endemic areas who are repeatedly exposed to ova. Because of complications from increased intracranial pressure and difficulty controlling seizures, these children may have a less favorable prognosis. Complications can arise from uncontrolled seizures, hydrocephalus, papilledema, and occasionally, headaches and emesis, although all of these complications are rare.

Race

Neurocysticercosis tends to be diagnosed more frequently in Hispanics because of the prevalence of the organism in the countries of origin, rather than an innate property of the host child.

Sex

No sexual predilection has been noted.

Age

Reports of cysticercosis are unlikely in children younger than 2 years because of the prolonged incubation period of T solium. Most often, the disease is recognized in children older than 7 years because of this incubation period.

Clinical

History

• The most characteristic feature in children is the acute onset of focal seizures.
  • Approximately 65-80% of children diagnosed with neurocysticercosis present with seizures, most often focal in nature.
  • Often, these children are brought to medical attention within 2 days of their initial seizure.
  • In many countries where T solium is endemic, cysticercosis is the major cause of epilepsy.
• Increased intracranial pressure (due to hydrocephalus, which can occur in 15-25% of cases) causes other common clinical symptoms, including headache, nausea, and vomiting.
• Less common presentations include hemiparesis, visual changes, progressive obtundation, sciatica (from cauda equina involvement), and sensory disturbances.
• In a 1996 study by Rosenfeld et al of 753 children in Chicago, none presented with fever.³
• Risk factors include the following:
  • Children who present with neurocysticercosis frequently have emigrated from an endemic area or are children of emigrants from such an area. In the past, many children were exposed to infection through Hispanic food handlers, but this occurrence is less common now.
  • Neurocysticercosis is endemic in certain communities because of poor sanitation, use of sewage for fertilizer, and lack of controlled pens for pigs.
  • If neurocysticercosis is a possible diagnosis in a child without such risk factors, question the family as to household contacts who have traveled to an endemic area. Remember that infection can precede symptoms by as much as 5 years.

Physical

• Most children with neurocysticercosis have normal findings on physical and neurologic examinations.
• Some patients may present with hemiparesis due to either a cyst or Todd paralysis after a focal seizure.
• Rarely, children may present with papilledema, hemiparesis, sensory disturbances, or palpable subdermal cysts.

Causes

• Larvae (cysticercus) of the tapeworm T solium cause neurocysticercosis. Larvae are acquired by ingestion of T solium ova, found in the feces of humans infected with the pork tapeworm.
• The disease is most common in the Developing World, especially in environments where sanitation is poor. Such environments exist in rural areas of Latin America, Asia, Africa, Spain, and Eastern Europe.
• Since the 1980s, this disease has been recognized more commonly in the United States, frequently in the states of California and Texas and in the city of Chicago, where Hispanics make up a large proportion of the community. The emergence of CT scanning and MRI studies as diagnostic tools also probably accounts for the increased detection since the 1980s.

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