Microbiology · Year 2 · from Microbiology
Case 1: Neurocysticercosis
Presentation
A 28-year-old man who immigrated from Mexico 5 years ago presents after having a witnessed generalized tonic-clonic seizure. He has no prior seizure history. He reports occasional headaches over the past few months. He has no fever. Neurological examination is non-focal. MRI of the brain reveals multiple cystic lesions of varying sizes scattered throughout the cerebral hemispheres; some lesions show ring enhancement, and several demonstrate calcifications. He has no history of eating raw pork, but he grew up in a rural area.
Clinical Image
Brain MRI demonstrating multiple cystic lesions characteristic of neurocysticercosis. Different lesion stages are visible: viable cysts (non-enhancing), degenerating cysts (ring-enhancing), and calcified lesions representing dead parasites.
Image Source: Lecture image - neurocysticercosis imaging
Questions
- What is the diagnosis, and what organism is responsible?
- How did this patient acquire the infection, and how does this differ from intestinal tapeworm infection?
- What do the different MRI lesion appearances represent?
- What is the approach to treatment?
Answers
- Diagnosis and organism: This is neurocysticercosis (NCC), caused by the larval stage (cysticercus) of the pork tapeworm Taenia solium. NCC is the most common parasitic CNS infection worldwide and the leading cause of acquired epilepsy in endemic regions. The diagnosis is supported by characteristic imaging, serologic testing (EITB - enzyme-linked immunoelectrotransfer blot), epidemiologic risk factors, and clinical presentation.
- Transmission mechanism: Critically, neurocysticercosis is acquired by ingesting T. solium eggs (from feces of a human tapeworm carrier), NOT by eating undercooked pork. The transmission occurs through:
- Fecal-oral transmission from a tapeworm carrier (often a household contact)
- Contaminated food or water containing eggs
Eating undercooked pork containing cysticerci causes intestinal taeniasis (adult tapeworm in the gut), not cysticercosis. The patient became an intermediate host (like a pig) when he ingested eggs; the eggs hatched, larvae penetrated the intestine, and disseminated to tissues (especially CNS, muscles, eyes).
- MRI lesion stages: The different lesion appearances represent stages of cysticercus evolution:
- Viable cysts: Fluid-filled, non-enhancing, with visible scolex ("hole-with-dot" sign)
- Colloidal/degenerating cysts: Ring enhancement around edematous, inflamed lesion as immune system attacks dying parasite
- Granular nodular stage: Retracting lesion with surrounding gliosis
- Calcified lesions: End-stage; represents dead, calcified parasites (may still cause seizures)
Multiple stages coexisting suggests infection over time or repeated exposures.
- Treatment approach:
- Antiepileptic drugs (AEDs): First priority for seizure control (levetiracetam, carbamazepine); may need long-term therapy
- Antiparasitic therapy: Albendazole (preferred) or praziquantel
- Indicated for viable parenchymal cysts
- Corticosteroids (dexamethasone) started before or with antiparasitic therapy to control inflammation from dying parasites
- Controversial/contraindicated for calcified-only disease, massive infection, or intraventricular cysts
- Calcified lesions only: AEDs alone; antiparasitics not indicated (parasites already dead)
- Intraventricular cysts: May require surgical removal to prevent hydrocephalus
- Ophthalmologic examination: Rule out ocular involvement before treatment (ocular cysts require surgery, not medical therapy)