Clinical Overview of Cysticercosis

Clinical features

Cysticercosis is caused by infection with the larval form (or cysticercus) of the tapeworm Taenia solium.

The period between initial infection and symptom onset varies from several months to many years.

Degeneration of a cyst may occur years after the initial infection. Some calcified cysts may intermittently release antigen, though this process is not fully understood. In the central nervous system (CNS), the inflammatory reaction and resultant edema appear as a contrast-enhancing ring around the cyst on imaging.

The number of cysticerci in the host can vary from one to more than 1,000. In the absence of massive numbers of cysticerci, the initial host tissue reaction is usually minimal. The developing cysticercus affects the surrounding tissue as a slowly growing mass that may cause pressure atrophy.

Signs and symptoms

In humans, cysticerci often occur in skeletal muscles. Less frequently, cysticerci may localize in the:

• Eyes
• Skin
• Heart

Clinical manifestations depend on the following characteristics of the cysts:

• Number
• Location
• Size
• Stage (viable, degenerating, or calcified)
• Intensity of the inflammatory response to degenerating cysts.

Most live cysts do not cause an inflammatory reaction. An acute inflammatory response occurs when the cysts degenerate, which results in the release of parasite antigens.

Most patients seek care due to cysts in the central nervous system (CNS), known as neurocysticercosis.

Neurocysticercosis

Epilepsy is the most common symptom of neurocysticercosis. It presents in 70% to 90% of symptomatic patients in published case series. Less frequent clinical symptoms include:

• Intracranial hypertension
• Hydrocephalus
• Chronic meningitis
• Cranial nerve abnormalities

There may be CSF pleocytosis as well. Necrotic larvae are completely or partially resorbed, but may become calcified, resulting in focal scarring that may provide a focus for seizures.

Neurocysticercosis may be parenchymal, which means it is in the brain substance. However, it could also be extraparenchymal, which means it is in one of the following:

• Meninges
• Ventricles
• Basilar cisterns
• Subarachnoid space of the brain or spinal cord

The distinction between parenchymal and extraparenchymal neurocysticercosis has important prognostic implications. Parenchymal disease with small numbers of cysts carries an excellent long-term prognosis (probably even without anthelminthic therapy) compared to parenchymal disease with > 50 cysts and extraparenchymal disease.

Prevention

To control and prevent cysticercosis, prevent fecal-oral transmission from people with taeniasis. From 1988 to 1991, 22% of locally acquired and 5% of imported cysticercosis cases reported to the Los Angeles County Health Department had active tapeworm carriers among family contacts. Identifying and treating carriers prevents further cases.

When traveling to areas with poor sanitation, people should be particularly careful to avoid foods that might be contaminated by human feces. Food handlers should be educated in good handwashing practices.

Based on investigations of cases of neurocysticercosis in U.S. citizens who acquired their infections from asymptomatic household employees from Latin America, CDC recommended that such employees should have stool examinations for taeniasis and be treated if found to be infected. CDC advises against routine testing of commercial food handlers. Instead, they suggested promoting policies for proper handwashing education and adherence.

Testing

Diagnosis usually involves both serological testing and brain imaging.

A patient may have clinical disease from a single or very few cysticerci. In this instance, serological results may be negative, but the lesions may be visible on imaging.

A patient may have cysticerci in locations other than the brain. In this instance, CNS imaging is negative but serological results might be positive, indicating an antibody response to lesions elsewhere (e.g., the spinal cord).

Treatment and recovery

The most urgent therapeutic interventions are aimed at managing neurological complications, and may require anticonvulsant therapy, corticosteroids, neurosurgical intervention and/or treatment of increased intracranial pressure.

Anthelminthic treatment may be indicated, but must be administered with caution, because larval death provokes an inflammatory response that may increase symptoms. Concomitant steroids are usually indicated.

It is now recognized that most infections are asymptomatic, or mildly symptomatic and benign. Mortality is low in patients with parenchymal cysts or calcification without hydrocephalus. However, untreated cysticercosis with any of the following can be life-threatening.

• Hydrocephalus
• Large basilar or supratentorial cysts
• Massive numbers of cysts
• Intracranial hypertension
• Cerebral infarction