eMedicine Specialties > Neurology > Neurological Infections

Neurocysticercosis

Author: Mohammed J Zafar, MD, FAAN, Associate Clinical Professor of Medicine, Kalamazoo Center for Medical Studies, Michigan State University; NeuroImager, Premier Medical Care, PC, Premier Radiology, Kalamazoo Neurologic Institute.
Contributor Information and Disclosures

Updated: Jul 1, 2009

Introduction

Background

Neurocysticercosis (NCC) is the most common parasitic disease of the nervous system and is the main cause of acquired epilepsy in developing countries. Lately, it has also been a problem in industrialized countries because of immigration of tapeworm carriers from areas of endemic disease.

See also, eMedicine article Neuroimaging in Neurocysticercosis.

Pathophysiology

NCC is the result of accidental ingestion of eggs of Taenia solium (ie, pork tapeworm), usually due to contamination of food by people with teniasis. T solium has a two-host biological cycle, with man as the definitive host carrying the intestinal tapeworm, and pig as the normal intermediate host harboring the larvae or cysticerci. It has a head (scolex) with 4 suckers and a double crown of hooks, an unsegmented neck, and a large body with several hundreds of hermaphrodite proglottids.

Cysticerci are ingested by humans through poorly cooked infected pork. Cysts evaginate in the small intestine, attach to the wall by its suckers and hooks, and develop strobila or chains of proglottids. From the distal end of the strobila, fertile eggs are excreted into the gravid proglottids. Up to 60,000 eggs may be contained in a proglottid. Pigs ingest stool contaminated with Taenia eggs, the embryos actively cross the intestinal wall, get into the bloodstream, and are transported to most tissues, where they reside as cysticerci. Larvae are found most commonly in the CNS, but they can also be located in the eye, muscle, or subcutaneous or other tissues.

Frequency

United States

NCC is mainly a disease of immigrants in the United States. Currently the disease is prevalent in the states of California, Texas, and New Mexico. It represents a major cause of morbidity among the Hispanic population. Most of the cases have been diagnosed in persons of Hispanic origin; however, because of travel to zones of endemic disease, the incidence is increasing in nonendemic countries. Native cases have been reported, presumably because of ingestion of infected food that was handled by carriers of T solium.

International

NCC is endemic in Central and South America, sub-Saharan Africa, and in some regions of the Far East, including the Indian subcontinent, Indonesia, and China, reaching an incidence of 3.6% in some regions. It is rare in Eastern and Central Europe, in North America (with the exception of Mexico), and in Australia, Japan, and New Zealand, as well as in Israel and in the Muslim countries of Africa and Asia. Cysticercosis can be seen in immigrant populations with a relatively high frequency, as in the southwest of United States and South Africa. NCC is the most common parasitic infection of the CNS. Approximately 2.5 million people worldwide carry the adult tapeworm, and many more are infected with cysticerci.

Mortality/Morbidity

No figures are available for the burden of mortality associated with NCC. However, the racemose¹ form of NCC, which appears macroscopically as groups of cysticerci, often in clusters that resemble bunches of grapes (see Media file 1), located in the subarachnoid space, is associated with poor prognosis and elevated mortality rate (over 20%). NCC-associated epilepsy is an important cause of neurological morbidity.²

Race

Subcutaneous cysticercosis is more common in Asian populations than in other peoples of other areas of endemic disease. It is not clear whether this is due to variations in parasite strain or to those in the host.

Sex

• NCC appears to affect men and women equally.
• Some evidence suggests that inflammation around parasites may be more severe in women than in men.³

Age

• Peak incidence is between ages 30 and 40 years.
• Although neurocysticercosis appears to be the most frequent cause of seizures in children⁴ and adults, the exact incidence in children is not known. The disease is increasingly commonly diagnosed with the routine use of diagnostic methods such as computed tomography (CT) and magnetic resonance imaging (MRI) of the brain.

Clinical

History

NCC is a pleomorphic disease, although it sometimes produces no clinical manifestation. This pleomorphism is due to variations in the locations of the lesions, the number of parasites, and the host's immune response.

• Many patients are asymptomatic; others report vague symptoms such as headache or dizziness.
• The onset of symptoms is usually subacute to chronic, with the exception of seizures, which present in an acute fashion. Patients may present with the following:
  • Epilepsy
    • Epilepsy is the most common presentation (70%) and is also a complication of the disease.²
    • NCC is the leading cause of adult-onset epilepsy and is probably one of the most frequent causes of childhood epilepsy in the world.
    • Seizures secondary to NCC may be generalized or partial. Simple and complex partial seizures may be associated with the presence of a single lesion. Generalized seizures are usually tonic-clonic; this is thought to be related to the presence of multiple lesions. However, irritation of focal cortical tissue by one of the lesions most probably leads to focal onset with secondary generalization. Myoclonic seizures also have been described.
  • Headache
    • Chronic headaches associated with nausea and vomiting (simulating migraines) 
    • Headaches associated with intracranial hypertension and indicative of hydrocephalus
    • Headaches due to meningitis
  • Intracranial hypertension
    • Most often, intracranial hypertension is due to obstruction of cerebrospinal fluid (CSF) circulation caused by basal or ventricular cysticercosis. It may also result from large cysts displacing midline structures, granular ependymitis, arachnoiditis, or the so-called cysticercotic encephalitis caused by the inflammatory response to a massive infestation of cerebral parenchyma with cysticerci.
    • These patients may have seizures and deterioration of their mental status, mainly due to the host's inflammatory reaction as an exaggerated response to the massive infestation.
  • Strokes⁵
    • Ischemic cerebrovascular complications of NCC include lacunar infarcts⁶ and large cerebral infarcts due to occlusion or vascular damage.
    • Hemorrhage also can occur, and has been reported as a result of rupture of mycotic aneurysms of the basilar artery.
    • Strokes may be responsible for the following signs and symptoms: paresis or plegias, involuntary movements, gait disturbances, or paresthesias.
  • Neuropsychiatric disturbances
    • These range from poor performance on neuropsychological tests to severe dementia.
    • These symptoms appear to be related more to the presence of intracranial hypertension than to the number or location of parasites in the brain.
  • Diplopia: This is a result of intracranial hypertension or arachnoiditis producing entrapment or compression of cranial nerves III, IV, or VI.
  • Hydrocephalus
    • Ten to thirty percent of patients with NCC develop communicating hydrocephalus due to inflammation and fibrosis of the arachnoid villi or inflammatory reaction to the meninges and subsequent occlusion of the foramina of Luschka and Magendie.
    • Noncommunicating hydrocephalus may be a consequence of intraventricular cysts.
• Other forms of neurocysticercosis
  • Intrasellar neurocysticercosis: Patients present with ophthalmologic and endocrinologic manifestations mimicking those of pituitary tumors.
  • Spinal NCC: This is rare. Spinal NCC may be either intramedullary or extramedullary. The latter is the most frequent and is responsible of symptoms of spinal dysfunction such as radicular pain, weakness, and paresthesias. Intramedullary presentation may cause paraparesis, sensory deficits with a level, and sphincter disturbances.
  • Ocular cysticercosis: This occurs most commonly in the subretinal space. Patients may present with decreased visual acuity, visual field defects, or monocular blindness.
  • Systemic cysticercosis: This is most common in the Asian continent. The parasites may be located in the subcutaneous tissue or muscle. Peripheral nerve involvement as well as involvement of liver or spleen have been reported.

Physical

Twenty percent or less of infected patients have abnormal neurological findings. Physical findings will depend on where the cyst is located in the nervous system and include the following:

• Cognitive decline
• Dysarthria
• Extraocular movement palsy or paresis
• Hemiparesis or hemiplegia, which may be related to stroke, or Todd paralysis
• Hemisensory loss
• Movement disorders
• Hyper/hyporeflexia
• Gait disturbances
• Meningeal signs

Causes

NCC can be acquired via fecal-oral contact with carriers of the adult tapeworm. This usually indicates the presence of a tapeworm carrier in the immediate environment (ie, household) or by accidental ingestion of contaminated food. Cases of autoingestion, in which persons with teniasis may ingest the eggs of T solium into their intestine, have been reported.

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