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Neurocysticercosis (NCC) — Basic to Advanced Medicine

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1. DEFINITION & OVERVIEW

"NCC is the most common cause of symptomatic epilepsy worldwide." — Bradley and Daroff's Neurology in Clinical Practice

• Parenchymal NCC — cysts within brain parenchyma (most common)
• Extraparenchymal NCC — cysts in ventricles, subarachnoid space, spine, or eye

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2. EPIDEMIOLOGY

• Endemic in Central/South America, sub-Saharan Africa, India, Eastern Europe, and parts of Asia
• An emerging infection in developed countries due to immigration and international travel
• In the USA, 33,060 cysticercosis-related hospitalizations recorded between 1998–2011 (rate: 8.03 per million population)

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3. LIFE CYCLE & PATHOGENESIS

The Dual Role of the Human Host

Step-by-Step:

1. A human tapeworm carrier sheds proglottids loaded with eggs in stool
2. Eggs contaminate food/water/hands via fecal-oral route (auto-infection possible in carrier)
3. After ingestion, oncospheres hatch in intestine, penetrate the mucosa
4. Haematogenous dissemination to brain, muscle, eye, subcutaneous tissue
5. Larvae mature into cysticerci in CNS tissue — initially immunologically tolerated ("phase of tolerance")
6. As the parasite begins to die, the host immune response is triggered → perilesional inflammation → seizures, edema, neurological deficits

Key point: You do not need to eat pork to get NCC. A strict vegetarian can develop NCC through fecal-oral transmission of eggs from a tapeworm carrier. — Sherris & Ryan's Medical Microbiology

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4. ANATOMICAL SUBTYPES

A. Parenchymal NCC (most common)

• Cysts lodge in the grey-white junction and cortex
• Progress through 4 stages (see Section 7 — Neuroimaging)
• Main presentation: focal seizures ± secondary generalization

B. Intraventricular NCC (second most common)

• Most often in the fourth and third ventricles, less commonly lateral ventricles
• Cysts are mobile (can migrate, documented on sequential imaging)
• Can cause acute obstructive hydrocephalus — a neurosurgical emergency

C. Subarachnoid / Racemose NCC

• Involves basal cisterns, sylvian fissures, cerebellopontine angle
• Racemose form: multiple clustered cysts separated by septa → classic "bunch of grapes" appearance
• Can cause large cystic lesions with meningeal nodular enhancement
• Higher morbidity; associated with basilar arachnoiditis and communicating hydrocephalus

D. Spinal NCC

• Rare; mimics intraspinal tumors
• Can be intra- or extramedullary

E. Ocular Cysticercosis

• Cyst in vitreous, subretinal space
• Can cause vision loss; surgical removal required

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5. PATHOLOGY & IMMUNOPATHOLOGY

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6. CLINICAL PRESENTATIONS

A. Seizures (most common — 50–70% of cases)

• New-onset focal seizures with or without secondary generalization
• Symptoms typically emerge ~5 years after initial infection
• In 80–90% of single-lesion cases, seizures resolve within 3–6 months as lesion calcifies
• Up to 20% develop refractory epilepsy requiring long-term AEDs

B. Raised Intracranial Pressure

• Due to intraventricular/subarachnoid cysts blocking CSF outflow → hydrocephalus
• Presents with headache, vomiting, papilledema
• Intraventricular cysts may cause sudden death from acute obstructive hydrocephalus

C. Focal Neurological Deficits

• Hemiparesis, hemisensory loss, cerebellar ataxia depending on cyst location

D. Meningitis / Encephalitis

• Basal arachnoiditis from subarachnoid NCC → cranial nerve palsies, communicating hydrocephalus
• Diffuse cysticercal encephalitis (rare) — mostly in children/young women with massive cyst burden → severe cerebral edema

E. Psychiatric Manifestations

• Cognitive impairment, personality change — recognized in Kaplan & Sadock's Comprehensive Textbook of Psychiatry

F. Spinal Cord Syndrome

• Cord compression or myelopathy

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7. NEUROIMAGING — THE FOUR STAGES

MRI (preferred) vs CT

"Cyst with a dot" sign — a CSF-signal cyst containing a small eccentric hyperintense scolex — is pathognomonic for viable NCC on MRI.

Special Forms on Imaging

• Racemose NCC: "bunch of grapes" multilobulated cystic mass in subarachnoid cisterns — no scolex visible
• Intraventricular NCC: Mobile cysts — FLAIR shows cyst as slightly hyperintense vs CSF; loss of flow void within ventricle
• Mixed stages: Multiple cysts at different stages simultaneously are common

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8. DIAGNOSIS — Del Brutto Revised Criteria (2017)

Absolute Criteria (definitive diagnosis if any one met):

1. Histologic demonstration of parasite from brain/spinal cord biopsy
2. Visualization of subretinal cysticercus on ophthalmoscopy
3. Conclusive demonstration of scolex within a cystic lesion on neuroimaging

Neuroimaging Criteria:

Clinical/Exposure Criteria:

Diagnostic Certainty:

• Confirmed: 1 absolute criterion OR 2 major criteria OR 1 major + confirmative neuroimaging + any clinical/exposure criterion
• Probable: 1 major neuroimaging + ≥2 clinical/exposure criteria (including ≥1 major)

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9. LABORATORY & SEROLOGICAL DIAGNOSIS

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10. TREATMENT

Guiding Principles

1. Number and viability of cysts
2. Location (parenchymal vs extraparenchymal)
3. Inflammatory state (edema, encephalitis)

Treatment Table by Form

Drug Details

Note: Dexamethasone reduces praziquantel levels by 50% via CYP3A4 induction — dose adjustment or preference for albendazole is recommended when combination therapy is used.

Seizure Management

• Antiepileptic monotherapy controls most seizures
• AEDs can be withdrawn after cyst resolution if no seizure recurrence
• Calcified lesions may cause chronic epilepsy requiring indefinite AED therapy

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11. INTRAVENTRICULAR NCC — ADVANCED SURGICAL CONSIDERATIONS

• Minimally invasive; direct cyst visualization and removal
• Avoids the need for open craniotomy
• For 4th ventricle cysts, approach choice depends on surgeon experience
• Antiparasitic therapy after surgical removal (not before — to avoid precipitating inflammatory hydrocephalus)

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12. COMPLICATIONS

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13. DIFFERENTIAL DIAGNOSIS

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14. PREVENTION

• Access to clean water and sanitation
• Handwashing before food preparation
• Thorough cooking of pork (kills cysticerci)
• Treatment of tapeworm carriers (praziquantel) to break the transmission cycle
• Mass drug administration programs in endemic communities
• Pig vaccination and treatment in endemic areas (veterinary public health)
• Improved pig husbandry — preventing pigs from accessing human feces

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15. RECENT EVIDENCE (2023–2025)

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SUMMARY FRAMEWORK

INGESTION OF T. solium EGGS (fecal-oral)
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  Oncospheres hatch → gut wall penetration
           ↓
  Haematogenous spread to CNS
           ↓
  Cysticercus forms (viable, silent)
           ↓
  Parasite begins to die → immune activation
           ↓
  Perilesional inflammation / edema
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  CLINICAL DISEASE (seizures, ICP, deficits)
           ↓
  Cyst dies → calcification
           ↓
  Chronic epilepsy or resolution

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