COMMENTARY

Neurocysticercosis: Leading Cause of Acquired Epilepsy Worldwide

Paul Cantey, MP, MPH

Disclosures

August 01, 2016

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Hello. I am Dr Paul Cantey, a medical epidemiologist at the Centers for Disease Control and Prevention (CDC). I am pleased to be speaking with you today as part of the CDC Expert Commentary Series on Medscape. Today I will be discussing neglected parasitic infections (NPIs), specifically neurocysticercosis.

Neglected Parasitic Infections

First, a little background on NPIs. NPIs are a group of five parasitic infections in the United States, which are targeted by CDC as priorities for public health action based on the number of people infected, the severity of the illnesses, and the ability to prevent and treat them. These diseases include Chagas disease, cysticercosis, toxocariasis, toxoplasmosis, and trichomoniasis.

Cysticercosis is infection with the encysted larval form of Taenia solium, or pork tapeworm (Figure 1).

Figure 1. Scolex of T solium. Image courtesy of CDC DPDx.

Cysticercosis and Neurocysticercosis

Cysticercosis is endemic in developing countries where pigs are raised in close contact with humans and sanitation is poor, including areas in Latin America, Asia, and sub-Saharan Africa. In the United States, infection is most common in persons who have immigrated from or traveled extensively to endemic areas.

The greatest risk factor for acquiring cysticercosis is close contact with someone who has an active intestinal infection with the pork tapeworm. An infected person who does not practice good hand hygiene may contaminate food with tapeworm eggs that have been shed in his or her feces, thus transmitting cysticercosis. Prevention recommendations include identification and treatment of tapeworm carriers and education about good hand hygiene practices for all food handlers. When in endemic countries, travelers should avoid food and water that may be contaminated with human feces.

Neurocysticercosis, which involves the central nervous system, is the most severe form of the disease and is often characterized by seizures or increased intracranial pressure. Approximately 50 million people worldwide have neurocysticercosis, and it is the leading cause of acquired epilepsy in many endemic countries. In the United States, approximately 2% of all emergency department visits for seizures are attributable to neurocysticercosis.[1] However, the disease is underreported in the United States because it is not a reportable disease in all states, the diagnosis is often not considered, and members of the high-risk groups often have poor access to care.

Neurocysticercosis is characterized by the presence of cysticerci (encysted tapeworm larvae) in the central nervous system. The disease can be parenchymal, occurring in the brain substance, or extraparenchymal, occurring in the ventricles, basilar cisterns, or subarachnoid space of the brain or in the spinal cord (Figure 2).

Figure 2. Gross of massive parenchymal cysts. Image courtesy of Ted Nash.

Patients may be asymptomatic or present signs or symptoms related to the number, location, size, and stage of the cysticerci and the host inflammatory response.

Cysticerci pass through three stages, which can be visualized on radiologic imaging: viable, when the parasite is alive; nonviable, when the parasite is dying; and calcified, when the parasite is dead (Figure 3).

Figure 3. Cyst death and degeneration during antihelminthic treatment (far left: viable stages; middle two images: degenerating cysts; far right image: calcified stage). Image courtesy of Ted Nash.

Diagnosis of Neurocysticercosis

Cyst stage influences both diagnosis and treatment. During the viable stage, a scolex, or the attachment organ of a tapeworm, may be seen on imaging. Antihelminthic treatment is most effective during this stage. During the nonviable stages, cysts can be either colloidal or granular. A scolex is sometime seen, and antihelminthics may sometimes be indicated. During the calcified stage, when the parasite is dead, antigen may be released, resulting in perilesional inflammation and edema seen in the calcified area. Antihelminthics are generally not indicated or effective during this stage.

Evaluation of patients with suspected neurocysticercosis should begin with a detailed history of residence in or extensive travel to endemic areas and consumption of food prepared by persons from endemic countries who may have a tapeworm infection. Neurocysticercosis can present with a variety of manifestations, including seizures, headaches, and intracranial hypertension. Diagnosis often requires both imaging and serologic testing; location and characteristics of lesions are essential to determine the best course of management.

Enzyme-linked immunoelectrotransfer blot (EITB) and ELISA testing are methods of serologically confirming radiologic results; EITB is the method preferred by CDC and is performed at a limited number of laboratories in the United States. ELISA is performed by many labs in the United States. Imaging with both CT and MRI is often needed; CT detects calcifications better and MRI detects extraparenchymal disease better. For patients presenting with intracranial hypertension or new-onset seizures, CT is the preferred initial imaging method. Radiologic scans should be reviewed carefully, because subtle signs of cysts may be missed on the initial reading.

Management of Neurocysticercosis

Management of patients with neurocysticercosis is a complex, evolving field, and must be individualized. The treatment goal is to control symptoms. Medication is recommended to control or prevent seizures, and corticosteroids are recommended when needed to control symptomatic inflammation and perilesional edema. Because the larvae do not move after encysting, corticosteroids will not result in migration of the parasite. Antihelminthics should be started only when it is safe to do so, such as after symptomatic inflammation is under control and all cysts have been characterized.

Neurosurgical consultation is indicated for increased intracranial pressure and the treatment of ventricular cysts. Prolonged antihelminthics and neurosurgical consultation are needed for subarachnoid disease. Consultation with a tropical medicine expert familiar with management of neurocysticercosis is highly recommended. For more information on neurocysticercosis, please visit CDC's resources for health professionals online, available at www.cdc.gov/parasites/cysticercosis.

Web Resources

Neurocysticercosis Continuing Education Unit

Cysticercosis

Cysticercosis Resources for Healthcare Professionals

Cysticercosis fact sheets (in English and Spanish)

Neglected Parasitic Infections

Parise ME, Hotez PJ, Shutsker L. Neglected parasitic infections in the United States: needs and opportunities. Am J Trop Med Hyg. 2014;90:783-785.
http://www.ajtmh.org/content/90/5/783.full

Cantey PT, Coyle CM, Sorvillo FJ, Wilkins PP, Starr MC, Nash TE. Neglected parasitic infections in the United States: cysticercosis. Am J Trop Med Hyg. 2014;90:805-809.
http://www.ajtmh.org/content/90/5/805.full.pdf+html

Woodhall D, Jones JL, Cantey PT, Wilkins PP, Montgomery SP. Neglected parasitic infections: What every family family physician needs to know. Am Fam Physician. 2014;89:803-811.
http://www.aafp.org/afp/2014/0515/p803.pdf

Estimating the Global Burden of Talenia solium/Cysticercosis Taeniosis

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