Neurocysticercosis

Definition
Neurocysticercosis is a parasitic infection of the central nervous system (CNS) caused by the larval stage (cysticercus) of the tapeworm Taenia solium. It is the most common cause of acquired epilepsy worldwide, particularly in regions where pork is consumed and sanitation is inadequate.

Etiology and Life Cycle

• Definitive host: Humans harbor adult T. solium tapeworms in the intestine, shedding eggs in feces.
• Intermediate host: Pigs ingest eggs, which develop into cysticerci in pig muscle tissue.
• Accidental human infection: Humans acquire neurocysticercosis by ingesting T. solium eggs (fecal‑oral transmission) from contaminated food, water, or hands. The eggs hatch in the intestine, releasing oncospheres that penetrate the intestinal wall, enter the bloodstream, and disseminate to various tissues, including the brain, where they develop into cysticerci.

Epidemiology

• Endemic in Latin America, sub‑Saharan Africa, South and Southeast Asia, and parts of Eastern Europe.
• Prevalence correlates with poor sanitation, free‑range pig rearing, and consumption of undercooked pork.
• Estimated to affect 2–5 million people worldwide, with higher incidence in rural settings.

Pathophysiology
Cysticerci can lodge in brain parenchyma, ventricles, subarachnoid space, or spinal cord. The disease progresses through four stages:

1. Vesicular stage: Viable cysts with a thin, translucent wall; minimal host inflammatory response.
2. Colloidal stage: Degeneration of cyst fluid triggers a robust inflammatory reaction, causing edema and mass effect.
3. Granular‑nodular stage: Further degeneration leads to thickened walls and reduced inflammation.
4. Calcified stage: Residual calcified lesions remain, often asymptomatic but can serve as epileptogenic foci.

Clinical Manifestations
Symptoms depend on cyst location, number, and stage:

• Seizures: Most common presentation, particularly with parenchymal cysts.
• Headache: Frequently associated with raised intracranial pressure or hydrocephalus.
• Focal neurological deficits: Result from mass effect or localized edema.
• Hydrocephalus: Ventricular cysts may obstruct cerebrospinal fluid flow.
• Meningitis or meningoencephalitis: Subarachnoid cysts can provoke meningeal irritation.
• Neurocognitive and psychiatric symptoms: Less common, may occur with extensive disease.

Diagnosis

1. Neuroimaging

   • Magnetic Resonance Imaging (MRI): Preferred; identifies cyst morphology, location, and stage.
   • Computed Tomography (CT): Useful for detecting calcified lesions and acute hemorrhage.

2. Serology

   • Enzyme‑linked immunoelectrotransfer blot (EITB) and ELISA assays detect antibodies against T. solium antigens; sensitivity varies with cyst burden and location.

3. Cerebrospinal Fluid (CSF) Analysis

   • May show eosinophilia, elevated protein, and lymphocytic pleocytosis, especially in subarachnoid disease.

4. Epidemiological Context

   • Travel or residence in endemic areas, exposure history, and dietary habits support clinical suspicion.

Treatment

• Antiparasitic Therapy

  • Albendazole (15 mg/kg/day) or praziquantel (50 mg/kg/day) administered for 7–28 days, often combined.
  • Therapy is generally indicated for viable cysts (vesicular/colloidal stages) but may be deferred in cases with severe edema or increased intracranial pressure.

• Adjunctive Corticosteroids

  • Dexamethasone or prednisone reduce inflammatory response to dying cysts, decreasing edema and seizure risk.

• Antiepileptic Drugs (AEDs)

  • Initiated for seizure control; duration depends on seizure recurrence after lesion resolution.

• Surgical Intervention

  • Indicated for obstructive hydrocephalus, large intraventricular cysts, or refractory seizures; procedures include ventriculoperitoneal shunting or endoscopic cyst removal.

Prevention

• Improved sanitation: Proper disposal of human feces to interrupt egg dissemination.
• Health education: Hand hygiene, safe food handling, and cooking pork thoroughly.
• Pig management: Controlled rearing, regular deworming, and confinement to reduce exposure to human feces.
• Vaccination of pigs: Experimental vaccines (e.g., TSOL18) reduce cysticercosis prevalence in pigs, indirectly lowering human infection risk.

Prognosis

• Most patients with parenchymal disease achieve seizure control and long‑term remission after appropriate therapy.
• Calcified lesions may persist indefinitely and can act as chronic seizure foci.
• Subarachnoid and ventricular forms are associated with higher morbidity and mortality due to complications such as hydrocephalus and meningitis.

See also

• Taenia solium infection
• Cysticercosis (systemic)
• Epilepsy epidemiology

References
(References are omitted per instruction format but would include peer‑reviewed sources such as WHO guidelines, Lancet infectious disease reviews, and neurology textbooks.)