OVERVIEW: What every practitioner needs to know
Are you sure your patient has cysticercosis? What are the typical findings for this disease?
Cysticercosis is caused by the cestode Taenia solium, or the pork tapeworm. Humans are the definitive host and pig is the intermediate host.
Cysticercosis in humans can affect the brain, spinal cord, eyes, muscles, and subcutaneous tissues. Cysticercosis of the brain and spinal cord is referred to as neurocysticercosis (NCC). NCC is the most serious of all forms of cysticercosis. T. solium is the most common parasite to infest the brain.
You should suspect NCC when a patient in an endemic region presents with seizures. Since the clinical manifestations of NCC are varied, there are no typical findings for this disease.
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What are the most common symptoms and signs of cysticercosis?
Focal neurologic deficits
Headache and vomiting can be caused by either cysts located in the ventricles causing hydrocephalus or parenchymal cysts associated with edema causing raised intracranial pressure (ICP). Occasionally the cysts are numerous and the condition is termed cysticercotic encephalitis.
NCC involving the spinal cord is rare and can cause gait disturbances, pain, transverse myelitis, paraparesis or quadriparesis. Cysticercosis involving the eye can cause blindness with or without proptosis. Cysticercosis of the subcutaneous tissues produces palpable subcutaneous nodules.
NCC of the brain causes the following clinical findings:
Seizures (80% of patients with NCC have this symptom) Headache and vomiting with or without altered sensorium
What other disease/condition shares some of these symptoms?
The differential diagnosis for cysticercosis includes many conditions and depends on the presentation of the patient.
Seizures: Seizures caused by NCC are typically partial in nature with or without secondary generalization. The differential diagnosis for NCC in the setting of seizures would include epilepsy, trauma involving the central nervous system, supartentorial tumors, supratentorial tuberculomas, and cerebral hemangiomas.
Headache and vomiting: Any pathologic condition that causes raised ICP should be considered, including meningitis/encephalitis, trauma, cerebellar tumors or tuberculoma, and intraventricular tumors.
Progressive focal deficits: Any mass lesion involving the cerebral hemispheres such as tumors, abscess, and tuberculomas should be part of the differential diagnosis.
Visual loss with or without proptosis: This symptom is caused by any orbital mass, such as hemangioma, retinoblastoma, lymphangioma, schwannoma, or rhabdomyosarcoma or by conditions such as optic neuritis or multiple sclerosis.
Subcutaneous nodules of cysticercosis: These nodules are mimicked by lipomas and neurofibromas.
What caused this disease to develop at this time?
Cysticercosis is caused by the consumption of uncooked food or water contaminated by eggs of T.solium, which are shed by a human carrier of the adult tapeworm. The eggs, which are contained in the gravid segments (proglottids) of the tapeworm, are perodically shed in the feces of the tapeworm carrier. Predisposing factors for acquiring this disease include the following:
Residence in/travel to a country with poor sanitation and open defecation
Unhealthy pig-rearing practices and lack of pork inspection
Poor personal hygiene (inadequate or no hand washing)
Although the disease is most commonly seen in people residing in areas with poor sanitation, it is also seen in those residing in developed countries who have traveled to endemic regions or, in some cases, have acquired the disease through contact with immigrants from regions with endemic taeniasis (Taenia carriers).
Only a complete clinical examination with imaging and laboratory studies can lead to a diagnosis, whether the predisposing conditions are present or not.
What laboratory studies should you request to help confirm the diagnosis? How should you interpret the results?
The best available laboratory test to diagnose cysticercosis is the enzyme-linked immunotransfer blot (EITB), which detects cysticercal antibodies in the serum and cerebrospinal fluid (CSF). Unfortunately, this test has low sensitivity in patients with a single cerebral cysticercal lesion or in those with calcified lesions, and sensitivity is higher in serum than in CSF. The specificity of the test is, however, high (>95%).
EITB is also not readily and universally available. An enzyme-linked immunosorbent assay (ELISA) test to detect antibody in the serum and CSF is available in the United States through the Centers for Disease Control and Prevention and several commercial laboratories. It has not accepted as a good test for neurocysticercosis.
Would imaging studies be helpful? If so, which ones?
Imaging is essential to make a diagnosis of NCC and ocular cysticercosis. The best options for imaging are contrast-enhanced computed tomography (CT) and/or contrast enhanced magnetic resonance imaging (MRI).
NCC can be categorized on the basis of the location of the cysts:
Parenchymal: Cysts pass through different phases, often ending with spontaneous involution.
Live cysts: These cysts appear as hypodense (on CT) and hypointense/hyperintense (on T1-weighted [T1W]/T2-weighted MRI ) rounded lesions measuring less than 2 cm without contrast enhancement or surrounding edema. The scolex (head) may be seen as a hyperdense or hypointense dot within the cyst (Figure 1).
Figure 1.
Live cysticercal cysts on T2W MRI of the brain. Note the scolex within the cysts seen as a hypointense dot.
Colloidal/granular stages: These cysts appear as peripherally enhancing rounded large (>2 cm) lesions (colloidal) or small (<2 cm) lesions (“ring” lesions; granulomas). Granulomas also may appear as solid rounded lesions smaller than 2 cm (“disc” lesions). There can be variable amounts of edema around these lesions. The scolex may be seen as an enhancing dot (“ring with dot”). A solitary cysticercus granuloma (SCG) is frequently the only manifestation of NCC (Figure 2 and Figure 3)
Figure 2.
Contrast CT showing a SCG in the right frontal lobe with surrounding edema.
Figure 3.
Gadolinium enhanced MRI showing an SCG.
Calcific stage: They appear as small calcific lesions usually measuring less than 1 cm with or without edema (Figure 4).
Figure 4.
Calcific residue of a cysticercus cyst.
Intraventricular: Usually live cysts are seen. These cysts can be of varying sizes ranging from a centimeter to several centimeters. The wall usually will not enhance, and the contents of the cyst will resemble CSF. Hence they may be difficult to diagnose.
Subarachnoid: Also called “racemose” cysts, these cysts are seen as widening of the subarachnoid spaces in which they lie. They do not have a scolex. They usually do not enhance after contrast injection.
All the different parenchymal forms and cysts in different locations may be seen in the same patient.
Other features: Hydrocephalus may be seen.
Ocular cysticercosis: The cysts lie either in the globe or in the orbit and may enhance with contrast, depending on the stage of the cyst.
Muscular and subcutaneous cysts: These are seen either as nonenhancing or enhancing cysts or calcifications (“cigar-shaped”).
Type of Imaging
Although MRI is more expensive, it is ideal because it avoids radiation exposure and is more sensitive for lesions that are near the base of the brain and in the ventricles.
Although a definitive diagnosis of NCC may not be made on the basis of CT or MRI in several cases, if a cyst is seen with an eccentrically placed mural nodule (“ring with dot”), almost always is diagnostic for cysticercosis.
All patients who are suspected of having NCC or ocular cysticercosis should undergo CT or MRI.
Confirming the diagnosis
No single diagnostic test is available to make a definitive diagnosis of NCC except for biopsy of the brain lesion. However, this is not necessary in most cases and could be associated with considerable risks.
The diagnosis of NCC is therefore based on diagnostic criteria that have been suggested by an expert group (Table I). These criteria incorporate clinical features and radiologic and immunologic tests and also take into account the location of the residence of the patient.
Table I.
| Absolute criteria | Major criteria | Minor criteria | Epidemiologic criteria | Definitive diagnosis | Probable diagnosis |
|---|---|---|---|---|---|
| Histologic demonstration of the parasite in a biopsy specimen from the brain | Positive serum EITB for cysticercal antibodies | Lesions on CT/MRI that are compatible with a diagnosis of NCC | Residence in an endemic region | One absolute criterion | One major + two minor criteria |
| Cystic lesion with a scolex on CT/MRI | Lesions highly suggestive of NCC on CT/MRI | Clinical features suggestive of NCC | Two major + one minor + epidemiologic criteria | One major + one minor + epidemiologic criteria | |
| Direct visualization of the subretinal parasite on fundoscopic examination | Spontaneously resolving single, small, enhancing lesion seen on CT | Positive CSF ELISA for cysticercal antibodies or antigens | Three minor + epidemiologic criteria | ||
| Resolution of intracranial cystic lesions with albendazole or praziquantel | Systemic cysticercosis |
Modified from Del Brutto OH, Rajshekhar V, White AC, et al. Proposed diagnostic criteria for neurocysticercosis. Neurology 2001;57:177-83.
However, these diagnostic criteria have not been evaluated for their sensitivity and specificity.
For patients with a solitary brain lesion there are criteria that have evolved and been evaluated prospectively. These criteria to diagnose an SCG have a sensitivity and specificity in the range of greater than 96%, with positive and negative predictive value in the same range.
These criteria are shown in Table II.
Table II.
| Clinical Criteria | CT Criteria |
|---|---|
| Patient should present with seizures | lesion should be solitary and enhanced with contrast medium |
| Patient should not have features of progressive neurologic deficits | The lesion should measure < 20 mm |
| Patient should not have features of persistent raised ICP | Edema, if present, should not produce a shift of the midline structures |
| There should be no evidence of a systemic disease (primary malignancy, systemic tuberculosis) |
;All criteria must be met for a preliminary diagnosis of SCG.
Adapted from: Rajshekhar V, Chandy MJ. Validation of diagnostic criteria for solitary cerebral cysticercus granuloma in patients presenting with seizures. Acta Neurol Scand 1997;96:76-81.
If you are able to confirm that the patient has cysticercosis, what treatment should be initiated?
Acute treatment
Seizures: Seizures should be controlled with antiepileptic drugs (AEDs). The commonly used AEDs are phenytoin sodium, valproic acid, carbamazepine, and newer AEDs such as levetiracetam. There is no evidence that any one of these is superior to the other in terms of efficacy or incidence of side effects. In some patients with seizures occurring at frequent intervals of a few hours, or in the case of status epilepticus, intravenous administration of a loading dose of phenytoin sodium or valproic acid and lorazepam may be needed.
Raised ICP: Dexamethasone or prednisolone, mannitol, and furosamide are used in the acute treatment of raised ICP.
Long-term treatment
Seizures: AEDs should be continued for several months, and in some patients will be required for several years. The duration of AED therapy in patients with SCG is guided by the follow-up imaging done approximately every 6 months or so. AEDs can be withdrawn soon after the resolution of the granuloma is demonstrated on the CT/MRI. (See Figure 5.)
Management algorithm for a patient with a suspected solitary cysticercus granuloma. (Modified from Rajshekhar V, Chandy MJ. Solitary cysticercus granuloma. Chennai, Orient Longman Ltd. , 2000
Raised ICP: Fursomide and oral glycerol can be used for periods longer than a week. Occasionally, steroid therapy with prednisolone or dexamethasone might be needed for several weeks in patients with cysticercotic encephalitis .
There are two cysticidal drugs; praziquantel and albendazole. These drugs are administered to patients with live cysts or granulomas and are not recommended for those with calcific lesions or a large number of granulomas (>100; cysticercotic encephalitis).
In patients with calcified lesions, the drug is unnecessary, whereas in those with cysticercotic encephalitis, the destruction of the cysts by the drug could lead to an acute elevation of ICP and death of the patient. Patients with subarachnoid cysts are also treated with these drugs. Finally, those with intraventricular cysts may be treated with cysticidal drugs if facilities for surgical intervention are unavailable.
Albendazole is preferred to praziquantel for its safety profile, lower cost, and easy availability. Also, albendazole levels in the serum are not lowered by simultaneous administration of steroids. Dosing schedules for these drugs follow:
Albendazole
Dose: 15 mg/kg/body weight in two divided daily doses (maximum 400 mg/kg twice daily)
Route: Oral
Duration: 8-30 days; most often for 15 days
Mannitol
Dose: 0.5-1 g/kg/body weight daily in four divided doses
Route: Intravenous
Duration: 48 to 72 hours
Furosemide
Dose: 2-4 mg/kg/body weight as a single dose/day
Route: Intravenous
Duration: 7-10 days
Oral glycerol
Dose: 1.5 mg/kg thrice daily
Route: Oral
Duration: Several weeks if needed
Surgery is infrequently needed in patients with NCC. It is most frequently needed for patients with intraventricular cysts and those with hydrocephalus. Intraventricular cysts need excision, and patients with hydrocephalus benefit from a ventriculoperitoneal shunt.
Spinal cord cysticercosis: Surgical excision of the cysts is the optimal therapy; cysticidal drugs with steroids are recommended when surgical facilities are not available.
Ocular cysticercosis: Surgical excision is the treatment of choice.
Subcutaneous cysts: No therapy is needed. A biopsy may be performed to confirm the diagnosis.
Muscular cysts: No therapy is needed.
What are the adverse effects associated with each treatment option?
Cysticidal drugs can cause rapid elevation of ICP resulting from an increase in edema caused by the death of the parasites. Therefore steroids should be coadministered with these drugs.
Long term use of albendazole (>1 month) can cause hepatic failure.
What are the possible outcomes of cysticercosis?
The prognosis is best for patients with SCG. Nearly 85% of patients with SCG can expect to be seizure free in the long term, after withdrawal of AEDs soon after the resolution of the granuloma on CT/MRI.
Those with intraventricular cysts also have a good outcome, with 70% of patients not requiring further therapy after surgical excision of the cysts.
Patients with multiple cysts and calcified cysts need treatment with AEDs for several years. In most patients, seizures will be well controlled with one or two AEDs. However, some patients may require multiple AEDs or may experience intractable epilepsy.
Treatment of seizures in patients with NCC is usually successful with one or two AEDs. The risks of treatment are those due to the adverse effects of AEDs.
What causes this disease and how frequent is it?
Cysticercosis is a zoonotic disease that involves pigs and humans. It has a worldwide prevalence, with transmission occurring mainly in the developing regions of the world with poor sanitation levels. It is commonly seen in children older than 2 years of age, although there are reports of NCC occurring in children younger than this. It is estimated that worldwide, nearly 50 million people are infected with cysticercosis and about 50,000 people die of the disease every year.
The normal life cycle involves humans as definitive hosts and pigs as intermediate hosts. Humans who harbor the adult tapeworm (Taenia carriers) shed Taenia eggs contained in the gravid segments of the worm (proglottids) in their feces. When the feces with the eggs is consumed by pigs it causes cysticercosis. In the pig, cysticercosis mainly affects the muscles. Consumption of undercooked or uncooked infected pork (measly pork) by humans leads to taeniasis.
Cysticercosis in humans (in which humans become the intermediate hosts) is an accidental occurrence and not part of the normal life cycle of the parasite. This occurs through consumption by humans of food or water contaminated by T. solium eggs. Pork consumption is not necessary to acquire cysticercosis. Therefore, vegetarians, Muslims, and Jews who do not consume pork can also get cysticercosis, but only those who eat pork can get taeniasis.
Although certain HLA types have been shown to be associated with cysticercus infection this has not been categorically proven.
How do these pathogens/genes/exposures cause the disease?
The Taenia eggs ingested with food or water penetrate the wall of the gut and reach the end organs through the blood supply. Once embedded in the tissue of the end organs such as the brain or muscle or eye, the egg develops into the larval form (cysticercus cellulosae).
The live cyst usually does not cause any symptoms. Symptoms are related to the degeneration of the wall, which occurs at a variable time, after the infection is established. The inflammation and edema around the cyst due to the leakage of the contents of the cyst cause the symptoms of seizures and raised ICP. Some live cysts in the parenchyma of the brain imbibe fluid from the surrounding tissues and become large enough to cause mass effect and produce focal deficits.
The intraventricular cysts cause symptoms by obstructing the ventricular pathways and producing hydrocephalus, which gives rise to symptoms of raised ICP.
Cysts in the subarachnoid spaces cause symptoms by blocking the outlet of the fourth ventricle or by causing arteritis and producing infarcts in the deep ganglionic structures or brain stem or by causing cranial neuropathies.
Other clinical manifestations that might help with diagnosis and management
There are three unusual clinical manifestations that have not been discussed previously.
Some patients with intraventricular cysts may present with features of sudden raised ICP due to the blockage of ventricular pathways such as at the foramen of Monro or the aqueduct.
Patients with cysts in the basal subarachnoid cisterns might present with features of a stroke because of arteritis of the small arteries in the basal cisterns.
NCC rarely produces spinal cord compression and can cause paraparesis or quadriparesis from an intramedullary cyst.
What complications might you expect from the disease or treatment of the disease?
Complications from the disease include complications from untreated seizures/epilepsy and status epilepticus, uncontrolled epilepsy or difficult-to-control epilepsy, and complications related to severe raised ICP such as altered sensorium, coma, or death.
Complications from the treatment include exacerbation of seizures due to inflammation from the death of cysts after use of cysticidal drugs, exacerbation of raised ICP due to the inflammation and edema surrounding dying cysts after use of cysticidal drugs, and focal deficits due to the edema around cysts destroyed by the cysticidal drugs.
Adverse effects of AEDs including Stevens-Johnson syndrome.
Are additional laboratory studies available; even some that are not widely available?
An ELISA has been developed to detect cysticercal antigens (Ag ELISA) in serum. This test more reliably detects active infection than does the EITB, which detects current or past infection/exposure or past infection. However, Ag ELISA is not commercially available.
How can cysticercosis be prevented?
The best prevention strategy for cysticercosis would involve improvement in sanitation levels so that pigs do not have access to human feces. However, since this goal is difficult to reach in several developing countries, other strategies have been suggested or implemented.
Strategies targeting pigs: corralling of pigs, mass therapy of pigs using oxfendazole to destroy cysts in pigs, vaccines against cysticercosis in pigs
Strategies targeting pork: meat inspection and destroying infected carcasses, freezing of pork
Strategies targeting humans: health education emphasizing use of toilets, hand washing, washing and cleansing of food that is consumed raw; adequate cooking of pork and other food; mass therapy of humans using praziquantel or niclosamide
What is the evidence?
Diagnostic criteria for NCC: Level III
Diagnostic criteria for SCG: Level II
Diagnostic test for NCC, EITB: Level II
Treatment for NCC: Level III
Del Brutto, OH, Rajshekhar, V, White, AC. “Proposed diagnostic criteria for neurocysticercosis”. Neurology. vol. 57. 2001. pp. 177-83. (Diagnostic criteria for neurocysticercosis were drawn up by a group of international experts on the disease.)
Del Brutto, OH, Roos, KL, Coffey, CS. “Meta-analysis: Cysticidal drugs for neurocysticercosis: albendazole and praziquantel”. Ann Intern Med. vol. 145. 2006. pp. 43-51. (Meta-analysis provided some evidence of benefit for the use of albendazole in certain categories of patients with neurocysticercosis.)
Garcia, HH, Evans, CAW, Nash, TE. “Current consensus guidelines for the treatment of neurocysticercosis”. Rev Med Microbiolo. vol. 15. 2002. pp. 747-56. (This article provides practical guidelines for the treatment of different forms of neurocysticercosis, although most of the guidelines had to be based on "expert opinion" in the absence of good quality evidence in most instances.)
Garcia, HH, Gonzalez, AE, Evans, CA. “Taenia solium cysticercosis”. Lancet. vol. 362. 2003. pp. 547-56. (This is a good overview of cysticercosis, including neurocysticercosis.)
Rajshekhar, V, Chandy, MJ. “Validation of diagnostic criteria for solitary cerebral cysticercus granuloma in patients presenting with seizures”. Acta Neurol Scand. vol. 96. 1997. pp. 76-81. (The authors present a prospective study validating the diagnostic criteria are reproduced above.)
Rajshekhar, V, Chandy, MJ. “Solitary Cysticercus Granuloma”. 2000. (A monograph on the subject of solitary cysticercus granuloma that provides a comprehensive coverage of the topic up until 2000.)
Rajshekhar, V, Jeyaseelan, L. “Seizure outcome in patients with a solitary cerebral cysticercus granuloma”. Neurology. vol. 62. 2004. pp. 2236-40. (A prospective study in 185 patients with SCG showing that 85% of patients had no seizure recurrence after withdrawal of antiepileptic drugs after granuloma resolution. Risk factors for recurrence of seizures are discussed.)
Rajshekhar, V. “Incidence and significance of adverse effects of albendazole therapy in patients with a persistent solitary cerebral cysticercus granuloma”. Acta Neurol Scand. vol. 98. 1998. pp. 121-3. (Adverse effects of albendazole therapy in patients with SCG are discussed in this article.)
Rajshekhar, V, Joshi, DD, Doanh, NQ. “Taenia solium taeniasis/cysticercosis in Asia: epidemiology, impact and issues”. Acta Trop. vol. 87. 2003. pp. 53-60. (This is an overview of epidemiology of cysticercosis and taeniasis in Asia.)
Rajshekhar, V. “Surgery for neurocysticercosis”. A review. Int J Surg. vol. 8. 2010. pp. 100-4. (This is a comprehensive review of surgical management in patients with neurocysticercosis.)
Sarti, E, Rajshekhar, V. “Measures for the prevention and control of Taenia solium taeniosis and cysticercosis”. Acta Trop. vol. 87. 2003. pp. 137-44. (Possible control strategies for cysticercosis and taeniasis and their pros and cons are discussed in this article.)
Ongoing controversies regarding etiology, diagnosis, treatment
The main controversy in the treatment of NCC revolves around the use of cysticidal drugs. Although there is no controversy regarding the fact that the drugs destroy the live larvae in the brain, some workers question whether destroying the larvae improves the seizure outcome in patients.
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